WEBVTT
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Michael Büker: Yes, alright, thank
you very much, okay. I’m glad
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that you all found your way here
and it’s been mentioned already,
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this is Comic Sans, which as you
know is the official type-font
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of awesome particle physics stuff.
laughter
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But in the interest of our mental
sanity, I will keep it to other fonts.
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So from here on Comic Sans
is just a bad memory.
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Okay, two things: First the
title, Breaking Baryons,
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which of course is an allusion
to Breaking Bad, was inspired
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by the wonderful talk from last year which
was called “How I Met Your Pointer”.
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And which was also very successful
and you can check out that talk,
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I got the link there. And this
talk goes especially well
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with another talk that we’ll have
tomorrow by a real particle physicist,
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at least a bit more than myself.
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And it’s called “Desperately Seeking
SUSY” which is about particle theories
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and the real cutting edge physical
questions. This is going to be
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happening tomorrow. Allright, so
we’re going to start out with my talk
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and I’m going to be talking about the
questions of “what are we doing?”,
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“why?” and “what kind of stuff do we
use?”. And I’m gonna spend some time
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on explaining this last part
especially. What is it that we do
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and how does this work? So, what
we do is we give a very high energy
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to small particles which
we call accelerating.
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But from a certain level of energy
this doesn’t really make sense,
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because we don’t actually make them go
faster. Once they reach the speed of light
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they can’t go any faster. We just
turn up the energy and the speed
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doesn’t really change. This is technically
useful but it also gives rise
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to doubts about the term accelerating,
but anyway, we just call it ‘accelerate’.
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There’s 2 basic types of devices that
you see there, you have storage rings,
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which are the circular facilities that
most of you know. And then there is
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linear accelerators which are in
comparison very boring, so I’m
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not going to be talking about them
a lot. We make the particles collide
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which is the reason for giving them high
energies, we want them to smash head-on.
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And then this last part which is about
the most difficult thing is we just
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see what happens. Which is not
at all as easy as it might sound.
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So why are we doing this? You all
know this formula but I’m going to try
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and put it in terms which are
a little bit closer to our hearts,
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as we are here at Congress.
I might postulate that
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parts, like electrical parts, building
parts, are actually the same as a device.
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Now this is not quite wrong but it
doesn’t feel exactly right, either.
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I mean, if you have some parts and then
build a device from it, it’s not the same.
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It’s made from the same thing but you do
require a certain amount of conversion.
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You have a building process, you have
specific rules how you can assemble
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the parts to make a device and
if you do it wrong it will not work.
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And this is actually pretty similar to the
notion of energy being equivalent to mass,
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because energy can be converted into mass
but it’s not at all easy and it follows
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a lot of very strict rules. But
we can use this principle
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when we analyze how particle
reactions are used to take a look at
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what mass and what energy forms
there are. Now suppose we are
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thinking about a device
which is very, very rare,
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such as a toaster that runs Net-BSD.
laughter
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Now as you can see from the photo
and the fact that you see a photo,
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I’m not making this shit up. There
is a toaster that runs Net-BSD but
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that’s beside the point. Now if we
are particle physicists and we want
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to research this question, we know
that parts are the same as a device,
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so if we just get enough parts and
do the right kind of things to them,
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there might just turn out, out of
nowhere a toaster that runs Net BSD.
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So let’s give it a try. We produce
collisions with technical parts
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and if we do enough of it, and if we
do it right, then there is going to be
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this result. Now from these pictures
you can see, that doesn’t seem
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to make a lot of sense. You will not
get a toaster from colliding vehicles.
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laughter
But as particle physics go,
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this is the best we can do. We
just smash stuff into each other
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and we hope that some other stuff
comes out which is more interesting.
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And that’s what we do. So to
put it in the technical terms,
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we use storage rings which are this
one circular kind of accelerator
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to produce collisions. Lots
of them with high energy.
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And then we put some enormous
experimental devices there
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and we use them to analyze what
happens. Now first let’s talk about
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these storage rings. This schematic
view is what a storage ring is
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mostly made of, and you can see right
away, that it’s not actually a circle.
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And this is true for any storage ring.
If you look at them closely they are
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not a perfect circle, you always
have acceleration parts which are
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not actually curved. So we
have the 2 basic elements
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of a curved part which is just “the
curve” and then you have a straight part
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which is there for acceleration. Now you
have this separation, it would be nicer
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to have a ring but it’s much more easy
this way. You have the acceleration
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where it is straight and because it is
straight you don’t need to worry about
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making the particles go on a curved
path. So you can just leave out
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the magnetic fields. We
need magnetic fields
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to keep them on a curve, but we need
electrical fields to accelerate them.
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Now we could try and assemble these
into one kind of device. A device
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that uses an electric field to accelerate
the particles and at the same time
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uses a magnetic field to keep them on
a curved path. Now this is the first thing
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that was tried. These kinds of
accelerators where called cyclotrons,
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but they were very inefficient, you
couldn’t go to high energies, it was
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very difficult. So the evolution went to
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this way where you just
physically separate the 2 tasks.
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You have a straight part for acceleration,
you have a curved part for the curve
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and then that’s much more easy.
Okay, so let’s take a look at the
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acceleration part of things. You
may know computer games
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where you go racing about and then
you have some kind of arrows
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on the ground and if you go over them in
the right direction they make you faster.
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This is a kind of booster if you will.
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If you happen to go around the wrong
way and you go onto these arrows,
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they will slow you down, which makes sense
because you’re going the wrong way,
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you shouldn’t be trying that. And this is
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the same effect we can think of when we
think about what an electrical field does
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to a charged particle. If a charged
particle moves through an electrical field
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in the ‘right’ direction so to speak
it will speed the particle up,
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taking energy from the field and to the
particle making it go faster. But if you
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go the wrong way, then this particle
will slow down and it will
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give off energy. If we where to try and…
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let’s say we have a level editor,
right? And we can edit this level
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where this little vehicle is going and
we want to make it go really fast.
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So what do we do? We just take this
acceleration path, we just take
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these arrows and we put them in a long
line. Let’s put 4, 5, 10 of them
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in a row, so if we go over them
we’ll be really fast at the end.
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Now suppose the level editor
does not allow this. It’s just
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by the rules of the game it’s not possible
to put a bunch of arrows in a row.
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Which sucks, because then we can’t
really make them go really fast.
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But then we just ask an engineer
who’s got this shit together.
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And what is he going to suggest?
You know what he’s going to suggest.
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Can I hear it? Come on, “inverse the
polarity”, that’s what he always does!
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laughter and applause
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So we inverse the polarity. And we are
going to make our track look like this.
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So we have an arrow which gives us a boost
in the right direction and then there’s
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an arrow in the wrong direction.
If we go over the track in this way,
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we’ll speed up and slow down and speed
up and slow down. And in the end
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we won’t win anything. But here is where
Geordi comes into play, because
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we’ll be switching polarities at just the
right moment and if we switch polarities
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at the precise moment that we are
in between two of these fields,
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then the next one will be an accelerating
field. And it goes on and on like this,
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we always switch the direction
of the arrows at the right moment
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when we are in between the two. And
from the point of view of the vehicle
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it will look like there is an accelerating
field followed by an accelerating field,
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followed by an accelerating field.
Which is the same as we tried to build
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but which the game, or in the case
of real accelerators the universe
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just wouldn’t allow. So we’re tricking
the universe by using Geordi’s tip
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and inversing the polarity at just the
right moments. And this is what is done
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in particle accelerators and this is
called Radio Frequency Acceleration.
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Now this kind of device that you see
there is the device that is used
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for this actual process in actual
accelerators. It’s about as big
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as a human child, but it
weighs a bit more, it weighs
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several hundred kilograms.
And in contrast to a child
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it’s made of a metal called Niobium.
Now Niobium is a rare metal,
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but it’s not super rare, and it fulfills
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3 basic requirements that
we have for these devices.
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It’s ductile, which means you can
easily shape it, because you see
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that this shape is really weird, you got
these kind of cone things going on,
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and they must be very precise. If these
cones on the inside of the cavity
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are off by just micrometers the whole
thing won’t work. So you need a metal
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which can be formed very well.
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Then you must be able to make it
superconductive, to cool it down
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to a temperature where it will
lose its electrical resistance.
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The electrical resistance will go down
to almost zero, some nano-Ohms
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is what’s left. So that’s the second
requirement for this metal,
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and the third one is: it shouldn’t
be ‘super’ expensive. I guess
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you could use platinum or something but
then you couldn’t pay for the accelerator
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and as we are going to see, the
accelerator is expensive enough as it is.
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So Niobium is what is used
for this kind of device and
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as I said, we cool it down to about
4 Kelvins, which is -269°C
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or 4°C above absolute Zero.
And at this temperature,
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the electrical resistance of the metal
is almost zero which we need
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for the high frequency
fields that we put in.
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What we used to cool these things is
liquid helium, so when they’re in use
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inside the accelerator they’re not
naked, exposed like you see here,
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they are enclosed by huge tanks
which are super tight and must
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hold on to large pressures and
be super temperature efficient,
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very well insulating
because these must keep
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the liquid helium inside. But on
the outside there is the tunnel
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of the accelerator and that’s where people
walk around. Not while the accelerator is
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running, but people walk around to do
maintenance and stuff. So you must have
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a temperature differential between room
temperature next to the accelerator
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and 4 Kelvin inside the tank
where this cavity is sitting.
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So you have a temperature difference
of 300 degrees, which this tank
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around the cavity must keep. So that’s
a very hard job, actually cooling
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is one of the more difficult things
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from an engineering point of view.
The thing which feeds the fields
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– the actual changing electrical
fields are polarity switched –
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into these cavities are called klystrons.
There’s a picture of a klystron,
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it’s the longish device sitting on the
bottom. And they’re usually about
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as big as a refrigerator or two.
And these klystrons produce
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radio waves not very much unlike that
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which you hear in your car when you just
turn on the radio. It’s not modulated
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in the same way, so there’s no
sound information encoded,
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but it’s extremely strong.
You can see on the bottom
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that one of these klystrons as it is in
use at the LHC has a transmitting power
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of 300 Kilowatts. Now if you think of the
transmitting power of the Fernsehturm
00:11:51.680 --> 00:11:54.860
like the Hertz-Turm which is right next
- no, that way -
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which is right next to the conference
center, or even the Fernsehturm in Berlin.
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It has about half the transmitting
power of one of these klystrons.
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Now for the LHC accelerator
16 of them are used.
00:12:06.389 --> 00:12:09.490
So that’s a lot of transmitting power.
And because the power is so high
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we don’t actually use cables.
Usually you transfer your…
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when you have some oscillator and
you’re checking out some signals,
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you just put cables between
your source and your device.
00:12:18.560 --> 00:12:22.620
This is not what’s used here, because
cables get way too complicated
00:12:22.620 --> 00:12:26.240
when you have these high energies.
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So what is used, is waveguides and that
is what you can see on the top there
00:12:28.750 --> 00:12:32.590
in this picture. It looks like an
air duct, it looks like there’s some
00:12:32.590 --> 00:12:36.089
sort of air conditioning system and the
air moves through. That’s not what it is.
00:12:36.089 --> 00:12:39.800
It is a waveguide which is designed
to have the radio waves inside
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radiate in a certain direction.
Think of a series of mirrors,
00:12:44.510 --> 00:12:50.620
long rectangular mirrors and you put
them all with the mirroring area inside.
00:12:50.620 --> 00:12:54.119
So you have a tube which is mirroring
inside. And then at one side
00:12:54.119 --> 00:12:57.090
you shine in a bright light. Now the
light can’t escape anywhere and it
00:12:57.090 --> 00:13:00.089
always hits the mirrors so it
goes on in a straight path.
00:13:00.089 --> 00:13:04.010
You’ve built yourself a waveguide
for light. Now this here,
00:13:04.010 --> 00:13:07.220
this clunky looking metal
part is a waveguide
00:13:07.220 --> 00:13:12.110
but for high frequency, high energy radio
waves which are fed into the cavities.
00:13:12.110 --> 00:13:16.040
And that’s how acceleration happens.
Now let’s talk about the curves.
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This is where it gets less
fidgety and more… boom!
00:13:21.490 --> 00:13:24.639
So these devices you see here, there’s
2 devices sitting next to each other,
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identical devices. These
are the cryo-dipoles.
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Again, they have the word “cryo” in
them because they are also cooled
00:13:30.290 --> 00:13:36.450
by liquid helium down to
a temperature of about -270°C.
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They’re 40 meters long, they weigh
35 tons and each of these babies
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costs about half a million Swiss Francs.
00:13:44.750 --> 00:13:49.670
And as you can see one line above that,
there’s 1200 of these curve dipoles
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in the LHC. So there you have
a cost of 1.5 to 2 billion dollars
00:13:54.719 --> 00:13:57.850
in the curve magnets alone.
We’re not talking acceleration,
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we’re not talking about power use, we are
not talking about the helium that you need
00:14:01.589 --> 00:14:05.550
for cooling or the power that you need for
cooling. It’s just building these things,
00:14:05.550 --> 00:14:08.769
just building the curve, 27 kilometers.
00:14:08.769 --> 00:14:12.250
And that’s what you have there as a
cost. Now what they do is, they make
00:14:12.250 --> 00:14:15.420
a huge magnetic field, because in
a magnetic field a charged particle
00:14:15.420 --> 00:14:19.300
will go on a curve. That’s
what we want, right? But
00:14:19.300 --> 00:14:23.970
to make these particles with a very high
energy and keep them on a tight curve…
00:14:23.970 --> 00:14:27.009
now in particle physics’ terms
let’s say that 27 kilometers
00:14:27.009 --> 00:14:30.920
to go around one way is a tight curve.
00:14:30.920 --> 00:14:35.459
We need a current of 12,000 amps.
Which is a large current
00:14:35.459 --> 00:14:38.579
that goes through these dipoles.
Which is the reason why we have them
00:14:38.579 --> 00:14:44.850
superconductingly cooled, because
otherwise you put 12,000 amps
00:14:44.850 --> 00:14:48.460
through a piece of metal and it just melts
away. You don’t get a magnetic field,
00:14:48.460 --> 00:14:52.820
maybe for a microsecond or 2.
But you want to sustain a stable field
00:14:52.820 --> 00:14:57.029
of 8.5 Tesla to make these
protons go around on a curve.
00:14:57.029 --> 00:15:00.890
So, yeah, that’s a big thing.
There’s also niobium in there,
00:15:00.890 --> 00:15:05.569
not the big clunky parts like the cavity
we saw, but thin niobium wires,
00:15:05.569 --> 00:15:09.500
actually half niobium, half titanium
most of the time. But since
00:15:09.500 --> 00:15:14.430
there are so many magnets and it’s
so long a curve, there is 600 tons
00:15:14.430 --> 00:15:18.759
of atomic niobium in this
entire accelerator thing.
00:15:18.759 --> 00:15:22.610
And this was a fourth of the
world production of niobium
00:15:22.610 --> 00:15:26.950
which comes mostly from Brazil by the way.
This was a fourth of the world production
00:15:26.950 --> 00:15:30.970
of niobium for 5 years.
So that’s where it all went.
00:15:30.970 --> 00:15:35.769
It just went into the accelerator.
And now if we have this running,
00:15:35.769 --> 00:15:39.259
we have it up, we have it cooled, we have
a large current going, we got our nice
00:15:39.259 --> 00:15:43.109
big magnetic fields. And
there is energy stored.
00:15:43.109 --> 00:15:46.910
I mean we put in a lot of power and the
magnetic fields are up and they’re stable
00:15:46.910 --> 00:15:50.920
and that means that there’s magnetic
energy stored in this. And the amount
00:15:50.920 --> 00:15:53.990
of energy that is stored in the curve
magnets alone of the LHC when it’s running
00:15:53.990 --> 00:15:58.009
is 11 gigajoules. Sounds like a lot,
00:15:58.009 --> 00:16:03.770
let’s compare it to something: If we
have an absurdly long freight train
00:16:03.770 --> 00:16:07.699
with let’s say 15,000 tons. I hear that
normal freight trains in Germany
00:16:07.699 --> 00:16:11.811
or England have about 5000 tons.
So let’s take a big freight train
00:16:11.811 --> 00:16:18.369
and multiply it by 3. If this
freight train goes at 150 km/h,
00:16:18.369 --> 00:16:21.899
then the kinetic energy, the
movement energy of this train
00:16:21.899 --> 00:16:26.839
is equivalent to the magnetic
energy that is stored in the LHC.
00:16:26.839 --> 00:16:29.969
And that is why we don’t want
any problem with the cooling.
00:16:29.969 --> 00:16:33.740
laughter
00:16:33.740 --> 00:16:39.740
Because if we get a problem with
the cooling, bad things happen.
00:16:39.740 --> 00:16:44.469
This is a photograph of what at CERN
at the LHC they just call “the incident”.
00:16:44.469 --> 00:16:47.089
laughter
00:16:47.089 --> 00:16:50.059
Which was a tiny mishap that
happened just a few weeks
00:16:50.059 --> 00:16:54.060
after the LHC was taken into
operation for the first time in 2008.
00:16:54.060 --> 00:16:57.230
And it shut the machine
down for about 8 months.
00:16:57.230 --> 00:17:00.390
So that was a bad thing. It’s
a funny story when they where
00:17:00.390 --> 00:17:03.290
constructing these magnets; now
what you see here is the connection
00:17:03.290 --> 00:17:07.850
between 2 of these magnets. I told you
that each of them weighs 35 tons.
00:17:07.850 --> 00:17:12.740
So here you have a connection between
2 parts that are 35 tons in weight each.
00:17:12.740 --> 00:17:18.100
And they’re shifted by almost half
a meter. So it takes a bit of boom.
00:17:18.100 --> 00:17:21.630
So what happened was: the cooling broke
down and the helium escaped and
00:17:21.630 --> 00:17:25.569
the sheer force of the helium expanding,
because if you have liquid helium
00:17:25.569 --> 00:17:29.810
and it instantly evaporates into gaseous
helium then the volume multiplies
00:17:29.810 --> 00:17:33.650
by a very large amount.
And what they had was…
00:17:33.650 --> 00:17:36.720
what I hear is that the tunnel of the
LHC, which has a diameter of about
00:17:36.720 --> 00:17:41.010
let’s say 6 or 7 meters was
filled with nothing but helium
00:17:41.010 --> 00:17:44.510
which pushed away the air
for about 100 meters
00:17:44.510 --> 00:17:48.140
around this incident. So the helium
evaporated, it pushed everything away,
00:17:48.140 --> 00:17:52.960
it made everything really cold, some
cables broke and some metal broke.
00:17:52.960 --> 00:17:57.010
And the funny thing now is, the
engineers that built the LHC,
00:17:57.010 --> 00:18:00.210
before they did that, visited
Hamburg. Because here there is
00:18:00.210 --> 00:18:03.511
a particle accelerator which is
not quite as large. The LHC
00:18:03.511 --> 00:18:07.770
has 27 kilometers; here in Hamburg we
have a particle accelerator called HERA
00:18:07.770 --> 00:18:12.490
which had 6.5 kilometers. So it’s
the same ballpark, it’s not as big.
00:18:12.490 --> 00:18:15.750
And in HERA they had a safety system
against these kinds of cryo failures,
00:18:15.750 --> 00:18:19.630
they’re called quenches.
They had a protection system,
00:18:19.630 --> 00:18:23.480
which protects this exact part.
Now we’re talking about “Yeah,
00:18:23.480 --> 00:18:26.710
how should we build this? Should
we have a quench-protection
00:18:26.710 --> 00:18:31.030
at the connection between the dipoles?”
And the HERA people in Hamburg said:
00:18:31.030 --> 00:18:34.690
“Well we have it, it’s a good thing,
you shouldn’t leave it out,
00:18:34.690 --> 00:18:38.630
if you build the LHC.” Well,
they left it out. laughter
00:18:38.630 --> 00:18:43.470
They ran out of time, they ran out of
money, the LHC project was under pressure.
00:18:43.470 --> 00:18:45.950
Because they had promised to build
a big machine by that time and
00:18:45.950 --> 00:18:49.450
they weren’t really finished, so they
cut some edges. Well this was
00:18:49.450 --> 00:18:53.930
the edge they cut and it cost them
8 months of operation. Which says
00:18:53.930 --> 00:18:59.360
that they really should have listened to
the people of Hamburg. Okay, so,
00:18:59.360 --> 00:19:03.940
in summary of the operations of
a storage ring we can just say this:
00:19:03.940 --> 00:19:07.040
They get perfectly timed kicks
with our polarity switching
00:19:07.040 --> 00:19:11.700
at just the right moment by radio waves
generated in these large klystrons
00:19:11.700 --> 00:19:16.110
from the funny looking metal
tubes that we called cavities.
00:19:16.110 --> 00:19:18.461
And some big-ass superconducting
magnets keep them on a curve
00:19:18.461 --> 00:19:22.780
when they are not being accelerated.
Now the trick is, one of these kicks
00:19:22.780 --> 00:19:26.430
like moving through the cavity once, may
not give you all the energy you want,
00:19:26.430 --> 00:19:30.160
in fact it doesn’t. But if you
make them go round in the ring,
00:19:30.160 --> 00:19:34.150
they come by every couple of
nanoseconds. So you just have them
00:19:34.150 --> 00:19:37.660
run through your acceleration all the
time. Which is the big difference
00:19:37.660 --> 00:19:40.620
between the storage ring and a linear
accelerator. A linear accelerator
00:19:40.620 --> 00:19:44.400
is basically a one shot operation but
here, you just give them an energy kick
00:19:44.400 --> 00:19:48.880
every time they come around, which
is often, we’re going to see that.
00:19:48.880 --> 00:19:52.880
So that’s the summary of what
the storage rings do. Now,
00:19:52.880 --> 00:19:56.570
the machine layout, if you
look at a research center
00:19:56.570 --> 00:20:01.160
which has a bunch of accelerators,
it almost always goes like this:
00:20:01.160 --> 00:20:05.030
You have some old, small storage
rings and then they built
00:20:05.030 --> 00:20:08.620
newer ones which were
bigger. So this is just
00:20:08.620 --> 00:20:12.420
a historical development, first
you build small machines, then
00:20:12.420 --> 00:20:14.920
techniques get better, engineering gets
better, you build bigger machines. But
00:20:14.920 --> 00:20:18.640
you can actually use that, it’s very
useful because the older machines,
00:20:18.640 --> 00:20:22.640
you can use as pre-accelerators.
For a variety of reasons it’s useful
00:20:22.640 --> 00:20:26.370
to not put in your particles with
an energy of zero and then
00:20:26.370 --> 00:20:30.180
have them accelerated up to the energy you
want. You want to pre-accelerate them,
00:20:30.180 --> 00:20:33.460
make them a little faster at a time.
That’s what you do, you just
00:20:33.460 --> 00:20:37.840
take the old accelerators. And if
we look at the accelerator layout
00:20:37.840 --> 00:20:42.200
of some real world research centers,
you can actually see this. On the left
00:20:42.200 --> 00:20:47.020
you have CERN in Geneva and on the
right you have DESY here in Hamburg.
00:20:47.020 --> 00:20:51.140
And you can see that there are smaller
accelerators, which are the older ones,
00:20:51.140 --> 00:20:54.140
and you have bigger accelerators
which are connected to them.
00:20:54.140 --> 00:20:59.410
And that’s this layout of the machines.
Okay, now let’s talk about collisions.
00:20:59.410 --> 00:21:03.411
This is a nice picture of a collision.
It’s not actually a proton collision
00:21:03.411 --> 00:21:08.270
but a heavy-ion collision, which
they do part of the time in the LHC.
00:21:08.270 --> 00:21:11.520
They are extremely hard to produce, we’re
going to see that, but still we make
00:21:11.520 --> 00:21:15.690
an awful lot of them.
So let’s see, first of all
00:21:15.690 --> 00:21:19.330
let’s talk about what the beam looks like,
because we’re going to be colliding beams.
00:21:19.330 --> 00:21:23.220
So what are these beams? Is it
a continuous stream of particles?
00:21:23.220 --> 00:21:27.780
Well it’s not. Because the acceleration
that we use, these radio frequency,
00:21:27.780 --> 00:21:31.960
polarity shifting mechanisms, they
make the particles into bunches.
00:21:31.960 --> 00:21:35.730
So you don’t have a continuous stream,
you have separate bunches.
00:21:35.730 --> 00:21:38.610
But how large are these bunches?
Is there one particle per bunch?
00:21:38.610 --> 00:21:41.150
You’ve got a particle, you wait
a while, there’s another particle?
00:21:41.150 --> 00:21:44.650
Well, it’s not like that.
Because if it were like that,
00:21:44.650 --> 00:21:49.300
if we had single particles coming after
one another, it would be impossible
00:21:49.300 --> 00:21:52.750
to hit them. You have to aim
the beams very precisely.
00:21:52.750 --> 00:21:56.620
I mean, think about it. One comes
around 27 kilometers around the ring.
00:21:56.620 --> 00:21:59.950
The other comes around 27
kilometers going the other way.
00:21:59.950 --> 00:22:03.480
And now you want them to hit. You have
to align your magnets very precisely.
00:22:03.480 --> 00:22:07.060
You can think of it like this:
You have a guy in Munich
00:22:07.060 --> 00:22:10.790
and you have a guy in Hamburg and
they each have a rifle. And the bullets
00:22:10.790 --> 00:22:14.550
of the rifle are let’s say one centimeter
in size. So the guy in Hamburg
00:22:14.550 --> 00:22:17.390
shoots in the air and the guy in Munich
shoots in the air, and they are supposed
00:22:17.390 --> 00:22:22.490
to make the bullets hit in the
middle, over, let’s say Frankfurt.
00:22:22.490 --> 00:22:25.720
Which they’re not going to manage.
And which is actually way too simple.
00:22:25.720 --> 00:22:32.200
Because if the bullet is really
one centimeter in size,
00:22:32.200 --> 00:22:37.360
then the equivalent distance that the two
shooters should be away from each other,
00:22:37.360 --> 00:22:40.650
if we want to make it the same
difficulty as these protons,
00:22:40.650 --> 00:22:45.050
would not be between Hamburg and Munich.
It would be from here to fucking Mars.
00:22:45.050 --> 00:22:49.470
laughter and applause
I calculated that shit.
00:22:49.470 --> 00:22:54.200
applause
00:22:54.200 --> 00:22:57.650
We don’t even have rifles on Mars
anyway. laughter
00:22:57.650 --> 00:23:01.690
So what we got is, we got large
bunches, very large bunches.
00:23:01.690 --> 00:23:04.890
And in fact there’s 10^11
protons per bunch, which is
00:23:04.890 --> 00:23:11.030
100 Billion. This is where I called Sagan
“ you going Millions of Millions“
00:23:11.030 --> 00:23:15.120
Okay, so you got 100 Billion
protons in one bunch.
00:23:15.120 --> 00:23:19.270
And the bunches go by one after the other.
Now, if you stand next to the LHC
00:23:19.270 --> 00:23:23.160
and you were capable of observing these
bunches, you would see one fly by
00:23:23.160 --> 00:23:28.170
every 25 nanoseconds. So you go “there’s
a bunch, now it’s 25 nanoseconds,
00:23:28.170 --> 00:23:32.770
there is the next one”. And there’s about
7.5 meters between the bunches.
00:23:32.770 --> 00:23:36.760
Now, 7.5 meters corresponds to
25 nanoseconds, you see that
00:23:36.760 --> 00:23:42.940
the speed is very big and indeed
it’s almost the speed of light.
00:23:42.940 --> 00:23:45.590
Which is just, we accelerate them
and at some point they just go
00:23:45.590 --> 00:23:48.640
with the speed of light and we just push
up the energy, we don’t make them
00:23:48.640 --> 00:23:53.750
go any faster actually. And if you
were to identify the bunches,
00:23:53.750 --> 00:23:58.940
which actually you can, you would
see that there are 2800 bunches
00:23:58.940 --> 00:24:02.890
going by; and then when
you have number 2809,
00:24:02.890 --> 00:24:06.620
that’s actually the first one that you
counted which has come round again.
00:24:06.620 --> 00:24:10.160
Per direction! So in total
we have over 5000 bunches
00:24:10.160 --> 00:24:15.470
of 100 Billion protons each. So
that’s the beam we are dealing with.
00:24:15.470 --> 00:24:19.610
Oh, and a funny thing: you get charged
particles moving, it’s actually a current,
00:24:19.610 --> 00:24:22.680
right? In a wire you have
a current running through it,
00:24:22.680 --> 00:24:27.150
there’s electrons moving or holes moving
and you get a current. If you were
00:24:27.150 --> 00:24:31.800
to measure the current of the
LHC, it would be 0.6 milliamps,
00:24:31.800 --> 00:24:34.330
which is a small current, but
we’re doing collisions anyway
00:24:34.330 --> 00:24:38.270
and not power transmission,
so that’s fine. laughter
00:24:38.270 --> 00:24:42.780
This is a diagram of what the actual
interaction point geometry looks like.
00:24:42.780 --> 00:24:46.340
You get the beams from different
directions, think of it like the top one
00:24:46.340 --> 00:24:50.010
coming from the right, the bottom
one coming from the left;
00:24:50.010 --> 00:24:53.480
and they are kicked into intersecting
paths by magnets. You have
00:24:53.480 --> 00:24:57.590
very complicated, very precise
magnetic fields aligning them,
00:24:57.590 --> 00:25:01.850
so that they intersect. And it’s
actually a bit of a trying-out game.
00:25:01.850 --> 00:25:05.970
I’ve heard this from
accelerator operators.
00:25:05.970 --> 00:25:09.410
You shift the position of the beams
relative to each other by small amounts
00:25:09.410 --> 00:25:12.880
and you just see where the collisions
happen. You go like: “Ah yeah, okay,
00:25:12.880 --> 00:25:17.220
there’s lots of collisions, ah, now
they’re gone, I’m going back.”
00:25:17.220 --> 00:25:20.440
And you do it like that. You can save the
settings and load them and calculate them
00:25:20.440 --> 00:25:24.300
but it’s actually easier
to just try it out.
00:25:24.300 --> 00:25:28.350
If we think of how much stuff we’ve
got going on: you got a packet,
00:25:28.350 --> 00:25:31.240
a bunch of 100 Billion
protons coming one way,
00:25:31.240 --> 00:25:35.100
you got another packet of 100 Billion
protons coming the other way.
00:25:35.100 --> 00:25:39.640
Now the interaction point area is as small
as the cross section of a human hair.
00:25:39.640 --> 00:25:43.270
You can see that, it’s one hundredth
of a square millimeter.
00:25:43.270 --> 00:25:46.110
Now how many collisions do
you think we have? We’ve got…
00:25:46.110 --> 00:25:48.120
Audience: Three!
Michael laughs
00:25:48.120 --> 00:25:51.850
Michael: …it’s actually not that bad.
We got about 20 in the LHC.
00:25:51.850 --> 00:25:56.450
And the funny thing is, people
consider this a bit too much.
00:25:56.450 --> 00:25:59.600
The effect is called pile-up. And the
bad thing about pile-up is you’ve got
00:25:59.600 --> 00:26:03.590
beams intersecting, you’ve got bunches
‘crossing’ – that’s what we call it.
00:26:03.590 --> 00:26:06.720
And there’s not just one collision which
you can analyze, there is a bunch of them,
00:26:06.720 --> 00:26:10.110
around 20. And that makes that
more difficult for the experiments,
00:26:10.110 --> 00:26:15.720
we’re going to see why. Well, and if we
have 20 collisions every bunch crossing
00:26:15.720 --> 00:26:19.580
and the bunches come by every
25 nanoseconds, that gives us a total
00:26:19.580 --> 00:26:24.690
of 600 Million collisions per
second. Per interaction point.
00:26:24.690 --> 00:26:27.770
Which we don’t have just one of. We
have 4 experiments, each experiment
00:26:27.770 --> 00:26:31.371
has its own interaction point. So
in total, we have about 2 Billion
00:26:31.371 --> 00:26:36.660
proton-proton collisions happening
every second when the LHC is running.
00:26:36.660 --> 00:26:39.580
Now let’s look at experiments.
laughs
00:26:39.580 --> 00:26:44.070
Yeah, this is a photograph of one part of
the ATLAS experiment being transported.
00:26:44.070 --> 00:26:47.690
And as for the scale of this thing, well,
in the physics community, we call this
00:26:47.690 --> 00:26:53.700
a huge device.
laughter
00:26:53.700 --> 00:26:57.150
I have a diagram of the experiment
where this is built in and
00:26:57.150 --> 00:27:00.510
you’re going to recognize the part
which is the one I’ve circled there.
00:27:00.510 --> 00:27:04.290
So the real thing is even bigger.
And down at the very bottom,
00:27:04.290 --> 00:27:08.190
just to the center of the
experiment, there’s people.
00:27:08.190 --> 00:27:12.860
Which if I check it like this,
they’re about 15 pixels high.
00:27:12.860 --> 00:27:16.490
So that’s the scale of the experiment.
00:27:16.490 --> 00:27:20.250
The experiment has the interaction point
at the center, so you got a beam line
00:27:20.250 --> 00:27:23.570
coming in from the left, you got the other
beam line coming in from the right.
00:27:23.570 --> 00:27:27.280
And in the very core of the experiment
is where the interactions,
00:27:27.280 --> 00:27:31.140
where the collisions happen. And then
you got the experiment in layers,
00:27:31.140 --> 00:27:35.240
like an onion, going around
them in a symmetrical way.
00:27:35.240 --> 00:27:38.370
Inside you have a huge magnetic
field which is almost as big
00:27:38.370 --> 00:27:42.470
as the curve magnets we were talking about
when I was describing the storage ring.
00:27:42.470 --> 00:27:46.130
This is about 4 Teslas,
so it’s also a very big field.
00:27:46.130 --> 00:27:50.160
But now we got a 4 Tesla field
not just over the beam pipe
00:27:50.160 --> 00:27:54.340
which is about 5 centimeters in diameter,
but through the entire experiment;
00:27:54.340 --> 00:27:58.080
and this thing is like 20-25 meters.
So you’ve got a 4 Tesla field
00:27:58.080 --> 00:28:01.910
which should span more than 20 meters.
00:28:01.910 --> 00:28:07.410
And, just for shits and giggles,
it’s got 3000 kilometers of cables.
00:28:07.410 --> 00:28:11.060
Which is a lot; and if you just
pull some random plug
00:28:11.060 --> 00:28:16.270
and don’t tell anyone which one it
was you’re making a lot of enemies.
00:28:16.270 --> 00:28:19.980
So the innermost thing is what we
call the inner tracking. It is located
00:28:19.980 --> 00:28:23.210
just centimeters off the beam line,
it’s supposed to be very very close to
00:28:23.210 --> 00:28:26.290
where the actual interactions happen.
00:28:26.290 --> 00:28:29.180
And this thing is made to leave the
particles undisturbed, they should just
00:28:29.180 --> 00:28:32.590
fly trough this inner tracking detector.
And the detector will tell us
00:28:32.590 --> 00:28:35.910
where they were, but not actually
stop them or deflect them.
00:28:35.910 --> 00:28:40.050
This gives us precise location data,
as to how many particles there were,
00:28:40.050 --> 00:28:44.030
what way they were flying,
and, from the curve,
00:28:44.030 --> 00:28:47.570
what momentum they have. Outside
of that we’ve got calorimeters.
00:28:47.570 --> 00:28:51.300
Now these are supposed to be stopping
the particles. A particle goes through
00:28:51.300 --> 00:28:55.360
the inner tracking without being disturbed
but in the calorimeter it should stop.
00:28:55.360 --> 00:28:58.970
And it should deposit all its energy there
and which is why we have to put around it
00:28:58.970 --> 00:29:03.100
the inner tracking. You see, if we put the
calorimeter inside, it stops the particle,
00:29:03.100 --> 00:29:07.770
outside of that nothing happens. So we
have the calorimeters outside of that.
00:29:07.770 --> 00:29:12.070
And then we got these funny wing things
going on. That’s the muon detectors.
00:29:12.070 --> 00:29:15.490
They are there for one
special sort of particle.
00:29:15.490 --> 00:29:19.610
Out of the… 50, let’s say 60
– depends on the way you count –
00:29:19.610 --> 00:29:22.860
elementary particles that we
have. These large parts are
00:29:22.860 --> 00:29:26.250
just for the muons. Because the
muons have the property,
00:29:26.250 --> 00:29:29.990
the tendency to go through all sorts of
matter undisturbed. So you just need to
00:29:29.990 --> 00:29:33.270
throw a huge amount of matter
in the way of these muons, like:
00:29:33.270 --> 00:29:36.750
“let’s have a brick wall and then
another one”. And then you
00:29:36.750 --> 00:29:42.030
may be able to stop the muons,
or just measure them.
00:29:42.030 --> 00:29:45.060
This is to give you an idea of the
complexity of the instrument
00:29:45.060 --> 00:29:49.170
on the inside. This is the inner tracking
detector, it’s called a pixel detector;
00:29:49.170 --> 00:29:52.730
and you see guys walking around in
protective suits. That is not for fun
00:29:52.730 --> 00:29:56.920
or just for the photo, this is a very,
very precise instrument. But it’s sitting
00:29:56.920 --> 00:30:00.100
inside this huge experiment which – again,
00:30:00.100 --> 00:30:03.910
I calculated that shit – is about
as large as a space shuttle
00:30:03.910 --> 00:30:07.420
and weighs as much as the
Eiffel Tower. And inside
00:30:07.420 --> 00:30:12.030
they’ve got electronics, almost a ton
of electronics which is so precise
00:30:12.030 --> 00:30:16.030
that it makes your smartphone
look like a rock. So there you go,
00:30:16.030 --> 00:30:19.970
it’s a very, very complicated sort of
experiment. Let’s talk about triggering,
00:30:19.970 --> 00:30:24.360
because as I said there’s 600 Million
events happening inside this.
00:30:24.360 --> 00:30:27.600
That’s 40 Million bunch crossings.
Now: how are we going to analyze this?
00:30:27.600 --> 00:30:31.720
Is there a guy writing everything
down? Obviously not.
00:30:31.720 --> 00:30:35.540
So this experiment with all the tracking
and the calorimeters and the muons
00:30:35.540 --> 00:30:39.800
and everything has about
100 Million electronic channels.
00:30:39.800 --> 00:30:43.410
And one channel could be the measurement
of a voltage, or a temperature
00:30:43.410 --> 00:30:47.330
or a magnetic field or whatever. So
we’ve got 100 Million different values,
00:30:47.330 --> 00:30:52.540
so to speak. And that makes
about 1.5 Megabytes per crossing,
00:30:52.540 --> 00:30:57.220
per every event readout. Which
gives us – multiplied by 40 Million –
00:30:57.220 --> 00:31:01.260
gives us about 60 terabytes
of raw data per second.
00:31:01.260 --> 00:31:05.610
That’s bad. I looked it up, I guess
00:31:05.610 --> 00:31:10.340
the best RAM you can do is about
1 terabyte per second or something.
00:31:10.340 --> 00:31:14.950
So we’re obviously not going to tackle
this by just putting in fast hardware,
00:31:14.950 --> 00:31:18.690
because it’s not going
to be fast enough. Plus,
00:31:18.690 --> 00:31:24.450
the reconstruction of an event is done
by about 5 Million lines of C++ code.
00:31:24.450 --> 00:31:29.570
Programmed by some 2000-3000
developers around the world.
00:31:29.570 --> 00:31:33.330
It simulates for one crossing
30 Million objects, which is
00:31:33.330 --> 00:31:36.840
the protons and other stuff flying around.
00:31:36.840 --> 00:31:44.410
And it is allocated to take 15 seconds
of one core’s computing time.
00:31:44.410 --> 00:31:47.770
To calculate it all, you would
need about 600 million cores.
00:31:47.770 --> 00:31:50.330
That’s not happening. I mean,
even if we took over the NSA
00:31:50.330 --> 00:31:54.132
laughter
and used all of their data-centers
00:31:54.132 --> 00:31:57.440
for LHC calculations, it still wouldn’t be
enough. So we have to do something
00:31:57.440 --> 00:32:02.570
about this huge mass of data. And
what we do is, we put in triggers.
00:32:02.570 --> 00:32:07.170
The trigger is supposed to reduce the
number of events that we look at.
00:32:07.170 --> 00:32:10.830
The first level trigger looks at
every collision that happens.
00:32:10.830 --> 00:32:13.840
And it’s got 25 nanoseconds
of time to decide:
00:32:13.840 --> 00:32:17.410
Is this an interesting collision?
Is it not an interesting collision?
00:32:17.410 --> 00:32:21.830
We tell it to eliminate
99.7% of all collisions.
00:32:21.830 --> 00:32:26.480
So only every 400th collision
is allowed for this trigger to go:
00:32:26.480 --> 00:32:30.280
“Oh, yeah, okay that looks interesting,
let’s give it to Level 2 trigger”.
00:32:30.280 --> 00:32:34.150
So then we end up with about 100,000
events per second. Which get us
00:32:34.150 --> 00:32:38.660
down to 150 Gigabytes per second. Now
we could handle this from the data flow,
00:32:38.660 --> 00:32:43.450
but still we can’t simulate it. So
we’ve got another level trigger.
00:32:43.450 --> 00:32:46.720
This is where the two
experiments at the LHC differ:
00:32:46.720 --> 00:32:50.030
the CMS experiment has just a
Level 2 trigger; does it all there.
00:32:50.030 --> 00:32:53.301
The ATLAS experiment goes the more
traditional way, it has a Level 2 trigger
00:32:53.301 --> 00:32:57.500
and a Level 3 trigger. In the end these
combined have about 10 microseconds
00:32:57.500 --> 00:33:01.450
of time, which is a bit more and it gives
them a chance to look at the events
00:33:01.450 --> 00:33:05.920
more closely. Not just, let’s say:
“Was it a collision of 2 protons
00:33:05.920 --> 00:33:09.300
or of 3 protons?”; “Were there
5 muons coming out of it
00:33:09.300 --> 00:33:12.810
or 3 electrons and 2 muons?” This is
the sort of thing they’re looking at.
00:33:12.810 --> 00:33:16.370
And certain combinations the triggers
will find interesting or not.
00:33:16.370 --> 00:33:20.120
Let’s say 5 muons, I don’t give a shit
about that. “3 muons and 2 electrons?
00:33:20.120 --> 00:33:23.480
Allright, I want to analyze it”. So
that’s what the trigger does.
00:33:23.480 --> 00:33:27.640
Now this Level 2 and 3 trigger,
again, have to kick out about
00:33:27.640 --> 00:33:31.070
99.9% of the events. They’re
supposed to leave us with
00:33:31.070 --> 00:33:36.360
about 150 events per second. Which
gives a data volume of a measly
00:33:36.360 --> 00:33:40.030
300 Megabytes per second and that’s
something we can handle. We push it
00:33:40.030 --> 00:33:45.780
to computers all around the world.
And then we get the simulations going.
00:33:45.780 --> 00:33:50.900
This is a display, this is
what you see in the media.
00:33:50.900 --> 00:33:55.360
If you take one of these events – just
one of the interesting events which
00:33:55.360 --> 00:34:00.740
actually reach the computers – because
those 40 million bunch crossings… well,
00:34:00.740 --> 00:34:04.150
most of them don’t reach the computers,
they get kicked out by the triggers.
00:34:04.150 --> 00:34:08.240
But out of the remaining 100 or 200
events per second, let’s say this is one.
00:34:08.240 --> 00:34:12.849
It’s an actual event and it’s been
calculated into a nice picture here.
00:34:12.849 --> 00:34:17.510
Now, normally they don’t do that, it’s
analyzed automatically by code
00:34:17.510 --> 00:34:21.089
and it’s analyzed by the physics data.
And they only make these pretty pictures
00:34:21.089 --> 00:34:25.339
if they want to show something to
the press. To the left you have
00:34:25.339 --> 00:34:29.330
what’s called a Feynman Diagraph.
That’s just a fancy physical way
00:34:29.330 --> 00:34:34.040
of saying what’s happening there. And
it involves the letter H on the left side,
00:34:34.040 --> 00:34:37.180
which means there’s a Higgs involved.
Which is why this event was particularly
00:34:37.180 --> 00:34:42.280
interesting to the people
analyzing the data at the LHC.
00:34:42.280 --> 00:34:47.230
And you see a bunch of tracks, you see
the yellow tracks all curled up inside,
00:34:47.230 --> 00:34:51.290
that’s a bunch of protons hitting
each other. The interesting thing is
00:34:51.290 --> 00:34:55.710
what happens for example above
there with the blue brick kind of things.
00:34:55.710 --> 00:35:00.050
There’s a red line going through
these bricks. This indicates a muon.
00:35:00.050 --> 00:35:05.480
A muon which was created in
this event there in the center.
00:35:05.480 --> 00:35:08.980
And it went out and the
bricks symbolize the way
00:35:08.980 --> 00:35:13.140
the reaction was seen by the experiment.
00:35:13.140 --> 00:35:16.880
There was actually just a bunch of bricks
lighting up. You got, I don’t know,
00:35:16.880 --> 00:35:21.320
500 bricks around it and brick 237
says: “Whoop, there was a signal”.
00:35:21.320 --> 00:35:24.300
And they go: “Allright, may have been
a muon moving through the detector”.
00:35:24.300 --> 00:35:28.700
When you put it all together you
get an event display like this. Okay,
00:35:28.700 --> 00:35:32.590
so we got to have computers analyzing
this. And with all the 4 experiments
00:35:32.590 --> 00:35:36.570
running at the LHC, which is not just
CMS and ATLAS I mentioned but also
00:35:36.570 --> 00:35:41.630
LHCb and ALICE, they produce about
25 Petabytes of data per year.
00:35:41.630 --> 00:35:46.230
And this cannot be stored at CERN alone.
It is transferred to data centers
00:35:46.230 --> 00:35:50.780
around the world by what is called
the LHC Optical Private Network.
00:35:50.780 --> 00:35:55.530
They’ve got a network of fibers going from
CERN to other data-centers in the world.
00:35:55.530 --> 00:36:00.430
And it consists of 11 dedicated
10-Gigabit-per-second lines
00:36:00.430 --> 00:36:04.410
going from CERN outwards. If we
combine this, it gives us a little over
00:36:04.410 --> 00:36:08.330
100 Gigabits of data
throughput, which is about
00:36:08.330 --> 00:36:11.880
the bandwidth that this congress has.
00:36:11.880 --> 00:36:14.560
Which is nice, but here it’s dedicated
to science data and not just porn
00:36:14.560 --> 00:36:20.250
and cat pictures.
laughter and applause
00:36:20.250 --> 00:36:23.930
applause
00:36:23.930 --> 00:36:27.580
From there it’s distributed outwards
from these 11 locations to about
00:36:27.580 --> 00:36:31.490
170 data centers in all the
world. And the nice thing is,
00:36:31.490 --> 00:36:35.090
this data, these 25 Petabytes
per year, is available
00:36:35.090 --> 00:36:38.310
to all the scientists working
with it. There’s about… well,
00:36:38.310 --> 00:36:41.440
everybody can look at it, but there’s
about 3000 people in the world
00:36:41.440 --> 00:36:45.270
knowing what it means. So all these
people have free access to the data,
00:36:45.270 --> 00:36:48.900
you and I would have free access to the
data, just thinking it’s cool to have
00:36:48.900 --> 00:36:53.260
a bit of LHC data on your harddrive maybe.
laughter
00:36:53.260 --> 00:36:57.850
All in all, we have 250,000
cores dedicated to this task,
00:36:57.850 --> 00:37:01.990
which is formidable. And about
100 Petabytes of storage
00:37:01.990 --> 00:37:05.730
which is actually funny, because
25 Petabytes of data are accumulated
00:37:05.730 --> 00:37:10.090
per year and the LHC has been
running for about 4 years.
00:37:10.090 --> 00:37:13.600
So you can see that they buy the
storage as the machine runs. Because
00:37:13.600 --> 00:37:17.540
100 Petabytes, okay, that’s what we have
so far. If we want to keep it running,
00:37:17.540 --> 00:37:21.730
we need to buy more disks. Right! Now,
00:37:21.730 --> 00:37:25.380
what does the philosoraptor
say about the triggers?
00:37:25.380 --> 00:37:29.110
If the triggers are supposed to eliminate
those events which are irrelevant,
00:37:29.110 --> 00:37:33.420
which is not interesting, well,
who tells them what’s irrelevant?
00:37:33.420 --> 00:37:37.230
Or to put it in the terms
of Conspiracy-Keanu:
00:37:37.230 --> 00:37:43.120
“What if the triggers throw away the
wrong 99.something % of events?”
00:37:43.120 --> 00:37:48.230
I mean, if I say: “If there’s an event
with 5 muons going to the left,
00:37:48.230 --> 00:37:52.500
kick it out!”. What if that’s actually
something that’s very, very interesting?
00:37:52.500 --> 00:37:56.010
How should we tell? We need to
think about this very precisely.
00:37:56.010 --> 00:37:59.320
And I’m going to tell you about
an example in history where
00:37:59.320 --> 00:38:02.800
this went terribly wrong, at least for
a few years. We’re talking about
00:38:02.800 --> 00:38:06.820
the discovery of the positron.
A positron is a piece of anti-matter;
00:38:06.820 --> 00:38:10.770
it is the anti-electron. It was
theorized in 1928, when
00:38:10.770 --> 00:38:15.440
theoretical physicist Dirac put up a bunch
of equations. And he said: “Right,
00:38:15.440 --> 00:38:20.030
there should be something which is like
an electron, but has a positive charge.
00:38:20.030 --> 00:38:22.470
Some kind of anti-matter.” Well,
that’s not what he said, but that’s
00:38:22.470 --> 00:38:26.740
what he thought. But it was
only identified in 1931.
00:38:26.740 --> 00:38:30.310
They had particle experiments back then,
they were seeing tracks of particles
00:38:30.310 --> 00:38:34.090
all the time. But they couldn’t
identify the positron for 3 years,
00:38:34.090 --> 00:38:37.210
even though it was there on paper.
So what happened? Well,
00:38:37.210 --> 00:38:41.230
you see the picture on the left. This
is the actual, let’s say baby picture
00:38:41.230 --> 00:38:44.460
of the positron. I’m going to
build up a scheme on the right
00:38:44.460 --> 00:38:48.440
to show you a bit more, to
give you a better overview of
00:38:48.440 --> 00:38:52.150
what we are actually talking about.
In the middle you’ve got a metal plate.
00:38:52.150 --> 00:38:55.200
And then there’s a track which is bending
to the left, which is indicated here
00:38:55.200 --> 00:39:01.890
by the blue line. Now if we analyze
this from a physical point of view,
00:39:01.890 --> 00:39:05.270
it tells us that the particle
comes from below,
00:39:05.270 --> 00:39:08.310
hits something in the metal plate
and then continues on to the top.
00:39:08.310 --> 00:39:12.900
So the direction of movement
is from the bottom to the top.
00:39:12.900 --> 00:39:17.310
The amount by which its curvature
reduces when it hits the metal plate
00:39:17.310 --> 00:39:21.780
tells us it has about the mass of
an electron. Okay, so far so good.
00:39:21.780 --> 00:39:26.020
But then it has a positive charge.
Because we know the…
00:39:26.020 --> 00:39:29.580
we know the orientation of the magnetic
field. And that tells us: “Well,
00:39:29.580 --> 00:39:33.280
if it bends to the left, it
must be a positive particle.”
00:39:33.280 --> 00:39:37.020
So we have a particle with the mass of
an electron, but with a positive charge.
00:39:37.020 --> 00:39:43.190
And people were like “Wat?”.
laughter
00:39:43.190 --> 00:39:46.160
So then someone ingenious came
up and thought of a solution:
00:39:46.160 --> 00:39:48.480
‘They developed the picture
the wrong way around!?’
00:39:48.480 --> 00:39:52.300
laughter and applause
00:39:52.300 --> 00:39:59.470
applause
00:39:59.470 --> 00:40:02.780
It’s what they thought. Well it’s wrong,
of course, there’s such a thing as
00:40:02.780 --> 00:40:08.500
a positron. And it’s like an electron,
but it’s positively charged. But…
00:40:08.500 --> 00:40:13.520
to put it in a kind of summary maybe:
you can only discover that
00:40:13.520 --> 00:40:17.180
which you can accept as a result.
This sounds like I’m Mahatma Gandhi
00:40:17.180 --> 00:40:23.200
or something but it’s just what we call
science. laughter
00:40:23.200 --> 00:40:27.740
Okay, so to recap: What have we
seen, what have we talked about?
00:40:27.740 --> 00:40:32.210
We saw from the basic principle,
that if we have energy in a place,
00:40:32.210 --> 00:40:36.190
then that can give rise to other forms of
matter, which I called ‘parts = a device’.
00:40:36.190 --> 00:40:39.360
You got your little parts, you do
some stuff, out comes a device.
00:40:39.360 --> 00:40:43.100
We have storage rings which give
a lot of energy to the particles
00:40:43.100 --> 00:40:46.700
and in which they move around in huge
bunches. Billions of billions of protons
00:40:46.700 --> 00:40:51.020
in a bunch and then colliding. Which
gives in the huge experiments
00:40:51.020 --> 00:40:55.390
that we set up an enormous amount of data
ranging in the Terabytes per second
00:40:55.390 --> 00:40:59.740
which we have to program triggers
to eliminate a lot of the events
00:40:59.740 --> 00:41:03.750
and give us a small amount of data which
we can actually work with. And then
00:41:03.750 --> 00:41:07.190
we have to pay attention to the
interpretation of data, so that
00:41:07.190 --> 00:41:11.500
we don’t get a fuck-up like with the
positron. Which is a very hard job.
00:41:11.500 --> 00:41:16.780
And I hope that I could give you
a little overview of how it’s fun.
00:41:16.780 --> 00:41:20.250
And it’s not just about building
a big machine and saying:
00:41:20.250 --> 00:41:24.180
“I’ve got the largest accelerator of
them all”. It’s a collaborative effort,
00:41:24.180 --> 00:41:28.600
it’s literally thousands of people working
together and it’s not just about
00:41:28.600 --> 00:41:32.390
two guys getting a Nobel Prize. You
see this picture on the top left, that’s
00:41:32.390 --> 00:41:36.900
about 1000 people at CERN watching
the ceremony of the Nobel Prize
00:41:36.900 --> 00:41:40.600
being awarded. Because everybody felt
there’s two people getting a medal
00:41:40.600 --> 00:41:45.230
in Sweden, but it’s actually an
accomplishment… it’s actually an award for
00:41:45.230 --> 00:41:49.190
everybody involved in this enormous thing.
And that’s what’s a lot of fun about it
00:41:49.190 --> 00:41:53.991
and I hope I could share some of this
fascination with you. Thank you a lot.
00:41:53.991 --> 00:42:19.000
huge applause
00:42:19.000 --> 00:42:22.410
Before we get to Q&A, I’m going to be
answering questions that you may have.
00:42:22.410 --> 00:42:25.560
My name is Michael, I’m @emtiu on
Twitter, I’ve got a DECT phone,
00:42:25.560 --> 00:42:29.550
I talk about science, that’s
what I do. I hope I do it well.
00:42:29.550 --> 00:42:32.210
And you can see the slides and
leave feedback for me please
00:42:32.210 --> 00:42:36.770
in the event tracking system. And
tomorrow, if you have the time
00:42:36.770 --> 00:42:39.720
you should go watch the “Desperately
seeking SUSY” talk which is going to be
00:42:39.720 --> 00:42:43.480
talking about the theoretical side of
particle physics. Okay, that’s it from me,
00:42:43.480 --> 00:42:46.540
now on to you.
Herald: Okay, if you have questions,
00:42:46.540 --> 00:42:50.240
please line up, there’s a mic there and
a mic there. And if you’re on the stream,
00:42:50.240 --> 00:42:53.770
you can also use IRC and
Twitter to ask questions. So
00:42:53.770 --> 00:42:55.820
I’m going to start here,
please go ahead.
00:42:55.820 --> 00:43:00.490
Question: Thanks a lot, it was a very
fascinating talk, and nice to listen to.
00:43:00.490 --> 00:43:04.030
My question is: Did HERA
ever suffer a quench event
00:43:04.030 --> 00:43:08.030
in which the quench protection
system saved the infrastructure?
00:43:08.030 --> 00:43:11.250
Michael: No, actually it didn’t. There
were tests where they provoked
00:43:11.250 --> 00:43:15.040
a sort of quench event in order to
see if the protection worked. But
00:43:15.040 --> 00:43:18.100
even if this test would have failed it
would not have been as catastrophic.
00:43:18.100 --> 00:43:22.020
But there were failures in the
operation of the HERA accelerator
00:43:22.020 --> 00:43:25.790
and there was one cryo failure. Which
is actually a funny story. Which is
00:43:25.790 --> 00:43:30.140
where one part of the
helium tubing failed
00:43:30.140 --> 00:43:33.680
and some helium escaped
from the tubing part
00:43:33.680 --> 00:43:36.790
and went into the tunnel. Now what
happened was that the air moisture,
00:43:36.790 --> 00:43:41.180
just the water in the
air froze at this point.
00:43:41.180 --> 00:43:45.450
And the Technical Director of the HERA
machine told us this: at one point
00:43:45.450 --> 00:43:49.020
he sat there with a screwdriver and
a colleague, picking off… the ice
00:43:49.020 --> 00:43:53.120
off the machine for half the night before
they could replace this broken part.
00:43:53.120 --> 00:43:56.480
So, yeah, cryo failures
are always a big pain.
00:43:56.480 --> 00:44:01.790
Herald: Do we have questions
from the internet? …Okay.
00:44:01.790 --> 00:44:04.490
Signal Angel: We have
one question that is:
00:44:04.490 --> 00:44:09.500
“How are the particles
inserted into the accelerator?”
00:44:09.500 --> 00:44:13.420
Michael: They mostly start
in linear accelerators.
00:44:13.420 --> 00:44:19.310
Wait, we’ve got it here. So you
got the series of storage rings
00:44:19.310 --> 00:44:23.780
there at the top in the middle and
you have one small line there.
00:44:23.780 --> 00:44:26.900
That’s a linear accelerator. To get
protons is actually very easy.
00:44:26.900 --> 00:44:30.400
You buy a bottle of hydrogen which
is just a simple gas you can buy.
00:44:30.400 --> 00:44:34.380
And then you strip off the electrons.
You do this by ways of exposing them
00:44:34.380 --> 00:44:38.280
to an electric field. And what you’re left
with is the core of the hydrogen atom.
00:44:38.280 --> 00:44:42.670
And that’s a proton. Then you
accelerate the proton just a little bit
00:44:42.670 --> 00:44:47.650
into the linear accelerator and from there
on it goes into the ring. So that means
00:44:47.650 --> 00:44:52.780
basically at the start of these colliding
experiments is just a bottle of helium
00:44:52.780 --> 00:44:56.590
that somebody puts in there. And
at the LHC it’s about, you know,
00:44:56.590 --> 00:45:00.430
a gas bottle. It’s about this big and it
weighs a lot. At the LHC they use up
00:45:00.430 --> 00:45:03.531
about 2 or 3 bottles a year for
all the operations, because
00:45:03.531 --> 00:45:07.760
a bottle of hydrogen
has a lot of protons in it.
00:45:07.760 --> 00:45:11.020
Herald: You please, over there.
00:45:11.020 --> 00:45:15.120
Question: Actually I have
2 questions: One part is,
00:45:15.120 --> 00:45:18.790
you said there are 2 beams
moving in opposite directions.
00:45:18.790 --> 00:45:22.680
And you explained the way where you
switched polarity. How can this work
00:45:22.680 --> 00:45:26.010
with 2 beams opposing each other?
00:45:26.010 --> 00:45:31.160
Michael: That’s a good question. Now, if
I show you the picture of the cryo dipole,
00:45:31.160 --> 00:45:36.980
you will see that these 2 beams
are not actually in the same tube.
00:45:36.980 --> 00:45:40.650
There we go. You see a cryo dipole and
00:45:40.650 --> 00:45:44.210
on the inside of this blue tube, you
see that there’s actually 2 lines.
00:45:44.210 --> 00:45:47.760
You can’t see it very well but
there’s 2 lines. So they are
00:45:47.760 --> 00:45:51.980
inside the same blue tube, but then
inside that is another small tube,
00:45:51.980 --> 00:45:56.040
which has a diameter of just about
a Red Bull bottle. Say 5 or 6 centimeters
00:45:56.040 --> 00:45:58.860
in diameter. And this is where the beam
happens. And they are just sitting
00:45:58.860 --> 00:46:02.480
next to each other. So the beams
are always kept separate
00:46:02.480 --> 00:46:06.310
except from the interaction points
where they should intersect.
00:46:06.310 --> 00:46:10.090
And the acceleration happens
obviously also in separate cavities.
00:46:10.090 --> 00:46:11.740
Herald: You had a second question?
00:46:11.740 --> 00:46:15.890
Question: The second question is: The
experiments, where are they placed,
00:46:15.890 --> 00:46:18.750
on the curve or on the acceleration part?
00:46:18.750 --> 00:46:22.610
Michael: The interaction points are
placed between the acceleration
00:46:22.610 --> 00:46:25.930
on the straight path. Because, again,
it’s much easier if you had the protons
00:46:25.930 --> 00:46:30.130
going straight for 200m; then you
can more easily aim the beam.
00:46:30.130 --> 00:46:34.240
If they come around the curve then they
have – you know they have a curve motion,
00:46:34.240 --> 00:46:38.000
you need to cancel that. That
would be much more difficult.
00:46:38.000 --> 00:46:39.410
Herald: And the left, please.
00:46:39.410 --> 00:46:42.630
Question: Okay, so you got yourself
a nice storage ring and then
00:46:42.630 --> 00:46:44.970
you connect it to the power plug
and then your whole country
00:46:44.970 --> 00:46:48.120
goes dark. Where does the power come from?
00:46:48.120 --> 00:46:52.510
Michael: Well, in terms of power
consumption of, let’s say
00:46:52.510 --> 00:46:56.950
households, cities, or aluminum plants:
00:46:56.950 --> 00:47:00.620
accelerators actually don’t
use that much power. I mean
00:47:00.620 --> 00:47:03.370
most of us don’t run an aluminum
plant. So we’re not used to this
00:47:03.370 --> 00:47:07.370
sort of power consumption. But’s it’s not
actually all that big. I can tell you about
00:47:07.370 --> 00:47:11.290
the HERA accelerator that we had here
in Hamburg, which I told you is about
00:47:11.290 --> 00:47:15.880
6.5 kilometers, not the 27, so you
can sort of extrapolate from that.
00:47:15.880 --> 00:47:20.230
It used with the cryo and the
power current for the fields
00:47:20.230 --> 00:47:25.030
and everything – it used about
30 MW. And 30 Megawatts is a lot,
00:47:25.030 --> 00:47:29.270
but it’s not actually very much in
comparison to let’s say aluminum plants,
00:47:29.270 --> 00:47:34.140
our large factories. But in fact,
the electricity cost is a big factor.
00:47:34.140 --> 00:47:38.530
Now you see the LHC is located at the
border between Switzerland and France.
00:47:38.530 --> 00:47:41.770
It gets most of its power from France.
00:47:41.770 --> 00:47:45.020
And you always have an annual shutdown of
the machine. You always have it off about
00:47:45.020 --> 00:47:47.890
1 or 2 months of the year. Where you do
maintenance, where you replace stuff,
00:47:47.890 --> 00:47:51.690
you check stuff. And they always
take care to have this shutdown
00:47:51.690 --> 00:47:55.500
for maintenance in winter. Because
they get their power from France.
00:47:55.500 --> 00:47:59.660
And in France many people use
[electrical] power for heating.
00:47:59.660 --> 00:48:03.670
There’s not Gas heating or Long
Distance heat conducting pipes
00:48:03.670 --> 00:48:07.480
like we have in Germany e.g. The people
just use [electrical] power for heat.
00:48:07.480 --> 00:48:11.500
And that means in winter the electricity
price goes up. By a large amount. So
00:48:11.500 --> 00:48:15.410
they make sure that the machine is off in
winter when the electricity prices are up.
00:48:15.410 --> 00:48:18.050
And it’s running in the summer where
it’s not quite as bad. So it’s a factor
00:48:18.050 --> 00:48:21.890
if you run an accelerator. And you
should tell your local power company
00:48:21.890 --> 00:48:25.130
if you’re about to switch it on!
laughter
00:48:25.130 --> 00:48:28.820
But actually, it won’t make the grid off,
even a small country like Switzerland
00:48:28.820 --> 00:48:30.890
break down or anything.
00:48:30.890 --> 00:48:35.150
Herald: Do we have more questions from
the internet? Internet internet, no,
00:48:35.150 --> 00:48:39.970
no internet. Okay. Then just
go ahead, Firefox Girl.
00:48:39.970 --> 00:48:43.000
Question (male voice): So you see a lot
of events. And I guess there’s many
00:48:43.000 --> 00:48:48.210
wrong ones, too. How do you select if
an event you see is really significant?
00:48:48.210 --> 00:48:51.470
Michael: Well, you have different kinds
of analysis. Like I told you there is
00:48:51.470 --> 00:48:57.750
100 Mio. channels you can pick from.
00:48:57.750 --> 00:49:01.960
With the simplest trigger that
you have, the Level 1 trigger,
00:49:01.960 --> 00:49:06.560
it can’t look at the data in much
detail. Because it only has 25 ns.
00:49:06.560 --> 00:49:09.910
But as you go higher up the chain,
as the events get more rare,
00:49:09.910 --> 00:49:13.320
you can look at them more closely. And
what we end up in the end, these 100,
00:49:13.320 --> 00:49:17.890
maybe 200 events per second, you can
analyze them very closely. And they get…
00:49:17.890 --> 00:49:20.990
they get a full-out computation. You
can even make these pretty pictures
00:49:20.990 --> 00:49:26.560
of some of them. And then it’s basically,
well, theoretical physicists’ work,
00:49:26.560 --> 00:49:29.161
to look at them and say: “Well, this
might have been that process…”, but
00:49:29.161 --> 00:49:33.060
still a lot of them get kicked out. When
the discovery of the Higgs particle
00:49:33.060 --> 00:49:37.540
was announced, it was ca. 1 1/2 years ago…
00:49:37.540 --> 00:49:42.470
Well, the machine had been running
for 2 1/2 years. And, like I told you,
00:49:42.470 --> 00:49:46.390
there’s about 2 Billion proton collisions
per second. Now the number of events
00:49:46.390 --> 00:49:51.150
that were relevant to the discovery
of the Higgs – the Higgs events –
00:49:51.150 --> 00:49:54.890
it was not even 100.
Out of 2 Billion per second.
00:49:54.890 --> 00:50:00.490
For 2 1/2 years. So you have to sort out
a lot. Because it’s very very, very rare.
00:50:00.490 --> 00:50:03.400
And that’s just the work of
everybody analyzing, which is why
00:50:03.400 --> 00:50:06.849
it’s a difficult task,
done by a lot of people.
00:50:06.849 --> 00:50:08.380
Herald: The right, please.
00:50:08.380 --> 00:50:13.060
Question: What I’m interested in: You
say ‘one year of detector running’.
00:50:13.060 --> 00:50:16.460
How much time in this year does
this detector actually run…
00:50:16.460 --> 00:50:18.140
…is it actually running?
00:50:18.140 --> 00:50:21.560
Michael: Well, yeah, like I said, we
have the accelerator off for about
00:50:21.560 --> 00:50:25.670
1 or 2 months. Then if something
goes wrong it will be off again.
00:50:25.670 --> 00:50:29.450
But you want to keep it running
for as long as possible, which…
00:50:29.450 --> 00:50:33.760
in the real world… let’s say it’s
9 months a year. That’s about it.
00:50:33.760 --> 00:50:35.260
Question: Straight through?
00:50:35.260 --> 00:50:38.570
Michael: Straight through – ah, well,
not in a row. But it’s always on
00:50:38.570 --> 00:50:41.350
at least for a week. And then you
get maybe a small interruption
00:50:41.350 --> 00:50:46.459
for a day or two, but you can also have
a month of straight operation sometimes.
00:50:46.459 --> 00:50:47.810
Herald: Internet, please!
00:50:47.810 --> 00:50:51.580
Signal Angel: Yeah, another question:
what would happen if they actually find
00:50:51.580 --> 00:50:54.820
what you are looking for?
Michael laughs
00:50:54.820 --> 00:50:58.690
Do we throw the LHC in the
dumpster or what do we do?
00:50:58.690 --> 00:51:01.930
Michael: That’s a good question!
It would be one hell-of-a waste
00:51:01.930 --> 00:51:06.310
of a nice-looking tunnel! laughs
You might consider using it for
00:51:06.310 --> 00:51:10.160
– I don’t know – maybe swimming
events, or bicycle racing.
00:51:10.160 --> 00:51:13.050
Well, but actually that’s a very good
question because the tunnel
00:51:13.050 --> 00:51:17.700
which the LHC sits in, this 27 km
tunnel, it was not actually dug,
00:51:17.700 --> 00:51:21.220
it was not actually made just for the LHC.
There was another particle accelerator
00:51:21.220 --> 00:51:25.620
inside before that. It had less energy,
because it didn’t accelerate protons
00:51:25.620 --> 00:51:30.030
but just electrons and positrons.
That’s why the energy was a lot lower.
00:51:30.030 --> 00:51:34.060
But they said: “Well, okay, we’re going
to build a very large accelerator,
00:51:34.060 --> 00:51:38.200
does anyone have a
30 km tunnel, maybe?”
00:51:38.200 --> 00:51:41.460
and then someone came up with:
“Yeah, well, we got this 27 km tunnel
00:51:41.460 --> 00:51:45.450
where this LEP accelerator is sitting in.
And when it’s done with its operations
00:51:45.450 --> 00:51:47.470
in…” – I don’t know, by that time,
let’s say in – “…10 years, we’re going
00:51:47.470 --> 00:51:51.900
to shut it off. Why don’t we put the next
large accelerator in there?” So you try
00:51:51.900 --> 00:51:55.860
to reuse infrastructure, but of course
you can’t always do that. The next big,
00:51:55.860 --> 00:52:00.470
the next huge accelerator, if we get the
money together as a science community,
00:52:00.470 --> 00:52:03.540
because the politicians are
being a bitch about it…
00:52:03.540 --> 00:52:06.920
if we get the money it’s going to be
the International Linear Collider.
00:52:06.920 --> 00:52:10.900
And that’s supposed to have
100 km of particle tubes
00:52:10.900 --> 00:52:16.240
and, well, you need to build
a new tunnel for that, obviously.
00:52:16.240 --> 00:52:20.050
Question: First off, couldn’t
you use it in something
00:52:20.050 --> 00:52:23.829
like material sciences, like
example with DESY?
00:52:23.829 --> 00:52:27.240
Well okay, if you are done with
leptons you can still use it
00:52:27.240 --> 00:52:30.590
for Synchrotron Laser
or something like this.
00:52:30.590 --> 00:52:33.500
Michael: That was thought of. The HERA
accelerator at DESY was shut off
00:52:33.500 --> 00:52:37.170
and people were thinking about if they
could put a Synchrotron machine inside it.
00:52:37.170 --> 00:52:41.670
But the problem there is the HERA
accelerator is 25 m below the ground.
00:52:41.670 --> 00:52:44.960
This is not enough space.
With particles accelerating
00:52:44.960 --> 00:52:48.730
you just need a small tube. But for
Synchrotron experiments you need
00:52:48.730 --> 00:52:51.810
a lot of space. So you would have
to enlarge the tunnel by a lot,
00:52:51.810 --> 00:52:56.210
and this was not worth it, in the case of
the HERA accelerator. But interestingly,
00:52:56.210 --> 00:53:00.000
one of the pre-accelerators of HERA,
one that was older is now used
00:53:00.000 --> 00:53:04.100
for Synchrotron science, which is
PETRA. Which used to be just an
00:53:04.100 --> 00:53:08.200
old pre-accelerator, and now it’s one of
the world’s leading Synchrotron machines.
00:53:08.200 --> 00:53:11.960
So, yeah, you try to reuse things
because they were expensive.
00:53:11.960 --> 00:53:15.630
Question: And may I just
ask another question?
00:53:15.630 --> 00:53:21.830
You said you get… you use just the matter
00:53:21.830 --> 00:53:25.420
from a bottle of hydrogen
or a bottle of helium.
00:53:25.420 --> 00:53:29.980
Well, most helium or hydrogen is protons
00:53:29.980 --> 00:53:33.850
or, in the case of helium, helium-4. But
00:53:33.850 --> 00:53:37.350
you have a little bit helium-3 or deuterium.
00:53:37.350 --> 00:53:41.150
And well, you are looking for
interesting things you don’t expect.
00:53:41.150 --> 00:53:44.880
So how do you differentiate if it’s really
00:53:44.880 --> 00:53:50.320
something interesting or: “Oh, one of
these damn deuterium nuclides, again!”
00:53:50.320 --> 00:53:54.100
Michael: You don’t get wrong isotopes
because you just use a mass spectrometer
00:53:54.100 --> 00:53:58.290
to sort them out. You have a magnetic
field. You know how large it is. And
00:53:58.290 --> 00:54:03.380
the protons will go and land – let’s say
– 2 micrometers next to the deuterons,
00:54:03.380 --> 00:54:07.230
and they just sort them out.
00:54:07.230 --> 00:54:11.240
Question: I have 2 questions. One is:
00:54:11.240 --> 00:54:15.100
I guess you mentioned that
basically once the experiment
00:54:15.100 --> 00:54:19.550
runs at speed of light you
just put more energy into it.
00:54:19.550 --> 00:54:22.380
But what is actually the meaning
of the energy that you put into it?
00:54:22.380 --> 00:54:25.230
What does it change in the experiment?
Like the Higgs was found
00:54:25.230 --> 00:54:28.260
at a particular electron volt…
00:54:28.260 --> 00:54:33.410
Michael: Yeah, it was
found at 128 GeV. Well,
00:54:33.410 --> 00:54:37.610
it’s more of a philosophical question.
There is a way of interpreting
00:54:37.610 --> 00:54:41.480
the equations of special relativity where
you say that, when you don’t increase
00:54:41.480 --> 00:54:45.930
the velocity you increase the mass.
But that’s just a way of looking at it.
00:54:45.930 --> 00:54:50.260
It’s more precise and it’s more
simple to say: you raise the energy.
00:54:50.260 --> 00:54:53.130
And at some low energies that
means that you raise the velocity.
00:54:53.130 --> 00:54:55.890
And at some high energies it means
the velocity doesn’t change anymore.
00:54:55.890 --> 00:55:00.110
But overall you add more energy.
It’s one of the weird effects
00:55:00.110 --> 00:55:07.769
of special relativity and there
is no very nice explanation.
00:55:07.769 --> 00:55:10.950
Question: Let’s assume there is
an asteroid pointing to earth.
00:55:10.950 --> 00:55:14.410
Michael laughs
Could you in theory point this thing
00:55:14.410 --> 00:55:17.980
on the asteroid and destroy it,
or would it be too weak?
00:55:17.980 --> 00:55:19.830
laughter
00:55:19.830 --> 00:55:24.290
applause
00:55:24.290 --> 00:55:26.750
Michael: I’m going to help you out.
Because it wouldn’t actually work
00:55:26.750 --> 00:55:30.430
because between the accelerator and the
asteroid there’s the earth atmosphere.
00:55:30.430 --> 00:55:33.750
And that would stop all the particles.
But even if there were no atmosphere:
00:55:33.750 --> 00:55:37.690
no, it would be much too weak. Well,
00:55:37.690 --> 00:55:40.620
you’d have to keep it up for a long time
at least. There was this one accident
00:55:40.620 --> 00:55:46.210
at the HERA accelerator where the
beam actually went off its ideal path
00:55:46.210 --> 00:55:50.300
and it went some 2 or 3 cm
next to where it should be.
00:55:50.300 --> 00:55:54.550
And it hit a block of lead – just,
you know, the heavy metal lead –
00:55:54.550 --> 00:55:59.070
and the beam shot into this
lead thing and the entire beam,
00:55:59.070 --> 00:56:02.960
which was a couple of Billions of
protons, was deposited into this lead
00:56:02.960 --> 00:56:06.670
and some kilograms of lead
evaporated within microseconds
00:56:06.670 --> 00:56:10.630
and there was a hole like pushed by
a pencil through these lead blocks.
00:56:10.630 --> 00:56:15.160
So, yeah, it does break stuff apart. But
even if you managed to hit the asteroid
00:56:15.160 --> 00:56:19.339
you would make a very small hole.
But you wouldn’t destroy it.
00:56:19.339 --> 00:56:26.800
It would be a nice-looking asteroid then.
laughter
00:56:26.800 --> 00:56:30.820
Question: Before you turned on the LHC
the popular media was very worried
00:56:30.820 --> 00:56:34.220
that you guys were going
to create any black holes.
00:56:34.220 --> 00:56:39.080
Did you actually see any black holes
passing by? Michael laughs
00:56:39.080 --> 00:56:43.080
Michael: Well, there may have been
some, but they were small, and
00:56:43.080 --> 00:56:48.810
they were insignificant. The interesting
thing is… sorry, I’m going to recap, yeah.
00:56:48.810 --> 00:56:52.010
The interesting thing is that whatever
we can do with the LHC – where
00:56:52.010 --> 00:56:56.869
we make particles have large energies
and then collide – is already happening!
00:56:56.869 --> 00:57:00.830
Because out in space there is black
holes with enormous magnetic fields
00:57:00.830 --> 00:57:04.450
and electrical fields. And these
black holes are able to accelerate
00:57:04.450 --> 00:57:08.320
electrons to energies much, much
higher than anything we can produce
00:57:08.320 --> 00:57:12.340
in any accelerator. The LHC
looks like a children’s toy
00:57:12.340 --> 00:57:16.370
in comparison to the energies that
a black hole acceleration can reach. And
00:57:16.370 --> 00:57:21.170
the particles which are accelerated in
these black holes hit earth all the time.
00:57:21.170 --> 00:57:24.630
Not a lot, let’s say one of these
super-energetic particles they come around
00:57:24.630 --> 00:57:28.840
about once a year for every
square kilometer of earth.
00:57:28.840 --> 00:57:31.470
But still, they’ve been hitting
us for Millions of years.
00:57:31.470 --> 00:57:34.900
And if a high-energy particle
collision of this sort were able
00:57:34.900 --> 00:57:39.140
to produce a black hole that swallows
up the earth it would be gone by now.
00:57:39.140 --> 00:57:45.499
So: won’t happen.
applause
00:57:45.499 --> 00:57:48.190
Question: Maybe more interesting
for this crowd: you talked about
00:57:48.190 --> 00:57:52.580
the selection process of the events.
00:57:52.580 --> 00:57:56.750
So I guess these parameters
are also tweaked to kind of
00:57:56.750 --> 00:58:00.430
narrow down like what
a proper selection procedure.
00:58:00.430 --> 00:58:04.040
Is there any kind of machine
learning done on this to optimize?
00:58:04.040 --> 00:58:07.230
Michael: Not that I know of. But there is
a process which is called ‘Minimum Bias
00:58:07.230 --> 00:58:11.690
Data Collection’. Where you
actually bypass all the triggers
00:58:11.690 --> 00:58:15.290
and you select a very small portion
of events without any bias.
00:58:15.290 --> 00:58:19.990
You just tell the trigger: “Take
every 100 Billionth event”
00:58:19.990 --> 00:58:22.940
and you just pass it through no matter
what you think. Even if you think
00:58:22.940 --> 00:58:28.150
it’s not interesting, pass it through.
This goes into a pool of Minimum Bias Data
00:58:28.150 --> 00:58:32.830
and these are analyzed especially in order
to see the actual trigger criteria
00:58:32.830 --> 00:58:37.230
are working well. So yeah,
there is some tweaking. And
00:58:37.230 --> 00:58:41.230
even for old machines
we have data collected
00:58:41.230 --> 00:58:44.910
and sometimes we didn’t know what we
were looking for. And some 20 years later
00:58:44.910 --> 00:58:48.800
some guy comes up and says: “Well,
we had this one accelerator way back.
00:58:48.800 --> 00:58:52.249
There may have been this and that
reaction. Which we just theorize about.
00:58:52.249 --> 00:58:56.200
So let’s look at the old data and see
if we see anything of that in there
00:58:56.200 --> 00:58:59.420
now, because it’s limited because
it goes through all the filters”.
00:58:59.420 --> 00:59:03.600
You can’t do this all the time with
great success. But sometimes,
00:59:03.600 --> 00:59:06.810
in very old data you find new
discoveries. Because back then
00:59:06.810 --> 00:59:11.980
people weren’t thinking about looking
for what we are looking now.
00:59:11.980 --> 00:59:16.470
Question: I always asked myself about
repeatability of those experiments.
00:59:16.470 --> 00:59:20.480
Seeing as the LHC is the biggest one
around there, so there’s no one out there
00:59:20.480 --> 00:59:23.320
who can actually repeat the
experiment. So how do we know
00:59:23.320 --> 00:59:26.440
that they actually exist, those particles?
00:59:26.440 --> 00:59:30.150
Michael: That’s a very good question.
I told you that there is 2 main
00:59:30.150 --> 00:59:33.940
large experiments. Which is the CMS
experiment and the ATLAS experiment.
00:59:33.940 --> 00:59:39.020
Now these both sit at the same ring.
They have some 10 km between them
00:59:39.020 --> 00:59:41.740
because they’re on opposite ends
of the ring. But still, obviously,
00:59:41.740 --> 00:59:46.690
they’re on the same machine. But these 2
groups, the ATLAS and the CMS experiment,
00:59:46.690 --> 00:59:51.910
operate completely separately. It’s not
the same people, not the same hardware,
00:59:51.910 --> 00:59:55.250
not the same triggers,
not even the same designs.
00:59:55.250 --> 00:59:58.760
They build everything up from scratch,
separate from each other. And
00:59:58.760 --> 01:00:02.700
it’s actually funny because when you
look at a conference and here is CMS
01:00:02.700 --> 01:00:05.570
presenting their results and here is
ATLAS presenting their results,
01:00:05.570 --> 01:00:08.300
they pretend like the other
experiment is not even there.
01:00:08.300 --> 01:00:11.730
And that’s the point of it: they’re
not angry at each other. It must be
01:00:11.730 --> 01:00:16.070
2 separate experiments because obviously
you can’t build a second accelerator.
01:00:16.070 --> 01:00:18.720
So you try to have redundancy in order
01:00:18.720 --> 01:00:22.900
for one experiment to confirm
what the other finds.
01:00:22.900 --> 01:00:27.900
Herald: Okay. It’s midnight
and we’re out of time.
01:00:27.900 --> 01:00:31.400
So please thank our awesome speaker!
applause
01:00:31.400 --> 01:00:39.163
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