Searching for the Genetic Code of our Universe: Joe Incandela at TEDxSalford

Translator: Robert Tucker
Reviewer: Tatjana Jevdjic So I’m going to tell you
about the discovery itself, but there’s quite a bit
I have to tell you before that and I have to do it
in a very short time. So we’re going to cover
all of quantum field theory, all of particle physics
in 18 minutes. (Laughter)
It’s no small – You’ll do fine. We’ll have an exam at the end. So this is our experiment,
the CMS experiment, I’ve titled the talk “Searching for the genetic code
of our universe.” What we do in particle physics,
in some sense, is very analogous to that and I hope I can show you
why that’s the case. Now like I said,
it’s quantum field theory, it’s Higgs field,
Higgs mechanisms, so we can get very, very obscure
very quickly, but what I’m gonna try to do is,
with a lot images and fairly simple analogies and some hopefully nice conceptualization
of some of these things, give you a sense of what we’re doing
and why we’re doing it and it how it works and why it’s interesting and hopefully
you could take some of this away with you. Now the title is also kind of pretentious,
I’d say, but that depends a bit
on your perspective. I asked a friend of mine who’s a physicist
studying string theory if she was interested in
what we might learn at the LHC. And she said,
“No, not really.” I said, “Why not?” and she said,
“Because it only pertains to our universe and you know –” So in some sense
this is a very modest talk, I’m only talking
about our universe here, OK. So I’m going to give you
some background. Now we have something we call
the Standard Model of particle physics and this took about 100 years
to put together, lots of theoretical physics
had to be developed, many subatomic particles
had to be discovered. And, it is really something like
a new periodic table of the most elementary particles
that we’ve built. This is what it looks like. There was a famous Nobel prize winner who flashed this slide
at one point and said, after decades and decades
of research and billions of dollars, “This is all we know.” But in a sense this is good,
this is what we want, we’d like to find a very simple,
underlying explanation of the universe. And what we discovered is that
there are three sort of generations of these kind of particles,
quarks and leptons, they’re fermions,
that means they have half-integer spin, you don’t have to worry about that. And those things, these particles,
are actually what build structure, build the atoms,
and things like this, and then are particles
that carry the force, sort of glue the other
particles together, very simple, and there’s a key piece,
other piece that we hadn’t found. So let me show you this again – this is one of the greatest achievements
of 20th century science. This is a look at the same particles, but you can see
their mass is on a log scale, so there’s quite a big difference
between the lightest and the heaviest, maybe a factor of a million. Actually we only see these particles, these make up the protons,
for example, and the atoms. But all the other ones turn out to be,
even though we can’t see them, very crucial to how
the universe is structured and how everything behaves and that’s why
we do what we do, and I’ll repeat that. There’s one missing piece
and that’s the Higgs particle, at least there was missing. Here you can see the masses of the quarks,
they go from really tiny to really high, and we don’t know why. That’s one of the things
we’d like to understand. OK, so what is the Higgs particle? So while we were developing this modern theory
of fundamental forces in these directions,
we kind of hit a snag. The particles that carry the forces have to be massless,
we knew that from our equations, but the data seemed
to indicate otherwise. And in fact we didn’t understand
why any particles should have mass or what was mass for that matter. Now massless particles,
they move at the speed of light, OK. And so theorists came up
with an ingenious idea: suppose there’s a force field
that fills the universe that somehow slows particles down
to below the speed of light. That would effectively give them mass. So in fact, as my predecessor was saying,
you have something like this. You have this field
that fills the universe, and as particles pass through it,
they get kind of caught up in it. Some more than others. And that’s how they become massive,
they basically become slowed down. And that’s what the Higgs field is. So what’s the difference
between a field and a particle? Now this is where it gets
a little bit counter-intuitive and it’s very hard to understand this
without studying quantum field theory. But fields have particles
associated with them; we call them field quanta,
from quantum mechanics, and they carry the force of that field. Particles interact in fact
by exchanging these force carriers. And here, for example,
I give you a very simple case, where you have electrons which are basically repelling
each other by exchanging a photon. So this is how forces work. There are other ways, other processes,
that are much more complex and they become very counter-intuitive
but this is a good way to look at things. Now quantum field theory
I’ve mentioned – The basis here is that energy
and mass are equivalent. So, strange things can happen,
actually, too, in quantum field theory. You can have a particle
and an antiparticle pop into existence
out of empty space. Something like this. Here you have 2 top quarks,
and then they can vanish back into it. This is called a quantum fluctuation
and these are virtual particles. It sounds a bit magical
but it’s actually really critical to everything we understand. And it has very
far reaching consequences. So, in fact the structure
of the universe turns out, because of these virtual particles
being everywhere, to depend on particles
that don’t exist in the usual sense. Some of which existed earlier, when the universe was much hotter
and much younger. And this is why we do what we do,
we’re trying to find these particles to understand how
they affect our universe. Here for instance is an event,
an event display, of some of the first
top quarks ever seen, in the 1990’s at Fermilab. So, what makes us so sure
that this Higgs particle should exist? Well, the theory
has very predictable consequences. For instance, it predicts
these very heavy force carriers of the weak nuclear force, the W and the Z particles. The W should have a mass
of about 80 GeV. Now this unit I’ll come back to
in a second. The Z should have a mass
of about 91 GeV and the proton has a mass of 0.9 GeV. So, these particles are much heavier
than the proton, even though they’re much smaller. Now, when they’re made,
they’re very unstable and they decay almost instantly. And we can see the tracks
of the decay products and we can see energy deposits
from the decay products in our detectors, and we can use these to reconstruct
the mass of the original particle [or] many of its other properties. So here’s, for example,
what we predict we would see if we look for Z particles
decaying to muons. You count the number of events
at different mass values, you’d expect to find a peak. This is what
a particle resonance looks like, a peak at the mass of 91.1. And then there’s some background
from other things. Now let me show you
what we actually see – this is it. The black dots show our measurements. So the Z and the W were exactly
as we predicted they would be, and this really made us take this idea
of the Higgs very seriously. Now there are fundamental connections
between particles and this is where
it gets kind of interesting. Fundamental particles actually
all interact with each other all the time, through these virtual reality
kind of interactions that I mentioned. So the mass of the W particle,
for instance, depends a lot on the mass of the top quark and a little bit
on the mass of the Higgs. And it is through
this kind of a process a W can decay into a top
and a bottom quark, and then those can fuse back together
and become a W again. A W can radiate a Higgs and re-absorb it
and become a W again. These things are happening all the time. Basically the identity of any
of these elementary particles is really not separable
from what it can become or decay into. And this is how the universe works
at a very, very basic level. How is this possible?
Well, here’s a good way to visualize it. The vacuum of space-time
is really a very interesting place. Imagine that you have
kind of an invisible fabric, that cloaks all these particles
that could exist and encodes how they could interact. That’s really what space-time is. Not anything can happen in space-time,
only these kind of things. These virtual particles are always waiting for an opportunity to interact
with real particles. So if you provide enough energy
in a very small region, you can pull particles
from this fabric into our reality. And to some extent
that’s exactly what we do. In fact if the energy is large enough,
we can pull up particles that are very heavy,
that we’ve never seen before. And these are the keys to understanding
the underlying code of our universe. So, how do you get a lot of energy
in one small spot? Well, we do it with what we call:
“Large Hadron Collider”. Let me show you that,
[I] have a nice picture of it. Basically we have rings of magnets
that focus beams and circulate them. Each time they go round we give them
a little acceleration with an electric field. And then when they get energetic enough
we switch them to another ring that’s bigger, we can make the particles accelerate
to even higher energies and then finally to this yellow one
which is the Large Hadron Collider. And it shows you the scale of things,
100 meters underground. It took a long time
to paint those stripes by the way. And here’s another view of it, and you can now get kind of a sense
of how big it is, because you can see Geneva airport, there,
it’s really quite a huge machine. And it is so huge
because the particles are accelerated to such high energies
that the magnets are limited in how well
they can keep them on track. So we have to build a very big machine,
and there we have four experiments. Two of them I’ll talk about a little bit today:
my experiments at CMS, or an experiment I’m part of,
I don’t own it, and ATLAS. But there are couple of others,
LHCb and ALICE that are very dedicated to very specific things
and I won’t go into those. It’s a bit like Swiss chocolate;
I’ll let you think about that for a second. The LHC magnets that keep
the particles on their track, they store a huge amount of energy. In fact, it’s enough
to melt 12 tons of copper, that’s how much energy
there is in these magnets. It is the kinetic energy
of an A380 at 700 km/h. How much energy is stored
in the actual beams? Well, it’s equivalent to 90kg of TNT
or 15kg of chocolate. I bet you didn’t know that chocolate
has more calories than TNT. OK, now let me tell you
about the experiments. The experiments are very big because we ram these protons together
at really high energy. Things can come out at really high energy
and we want to measure those things. We have to build
very, very large experiments to be able to bend the particle tracks
in magnetic fields and actually measure their momenta. So here’s ATLAS and I’ll show you
how it looked as it was being built. This is 30 storeys underground and there you see
a person standing amids it. Now lots get filled in here in fact and I’ll show you in fact
with CMS a little bit more. ATLAS is just like CMS in the sense
that there’s about 40 countries involved, hundreds of institutions
and thousands of physicists. So CMS, this is the experiment
I’m heading right now, we had to build it on the surface
and then lower it. And this piece right here,
the central piece of the experiment, is 4.4 million pounds and had to be lowered 30 stories
with only, if you look there, we had 3 inches of clearance,
so it was quite tricky to do that. And here, this sets the scale,
if you go back to this picture, you see the magnets, comes hard to tell
how big this giant solenoid magnet is, if come here you can see, it’s quite big,
it’s the largest magnet ever built. We also recycled some things to build, actually old casings
from the Russian military, were made into
parts of our experiment. And here I show what’s happening
as we’re inserting the central tracking system. OK, and then this is the picture
I showed at the beginning, this is when the detector
was ready to close this is actually the beam line here –
OK? And that’s where the protons go
and then they collide in the center of the detector
which is a bit over here to the left. OK, there are a lot of people involved, this is 1/8th of the people
that were involved in the CMS experiment. And as the presenter mentioned
before me there were about 4000 people
involved altogether. OK, so how do we reconstruct
what happens in a collision? This is the detector looked at end on and you notice it’s kind of got
a lot of cylinders involved. And if I replace it with a cartoon,
you can see this. All the different cylinders
are different kinds of detectors that detect different properties of the particles
as they pass through them. And when we sum up all the information
from all the different layers, we can tell if they’re pions,
muons, kaons, etc. And that’s how we reconstruct
these things. Now we collide these two beams
of protons, as I mentioned, each beam has 1380 bunches,
each bunch has 160 billion protons. Lots of numbers,
they collide 4 different places, and whenever they cross, even though there’s a 160 billion protons
in each bunch, you only get about 20 or 30 pairs
of protons that collide. And usually what happens is,
they just break up. The proton breaks up,
the quarks go flying out, and you make new particles,
but it’s not very interesting. Sometimes though,
it gets very interesting. Let me just show you a simple event,
this is our first event of the 2012 era, And this is a real event,
everything you’re seeing now is simulated, but you’ll see what the event actually
looks like when the two bunches cross – Here’s 30 pairs of protons fly, and those are the tracks
of the particles coming out, and the blue represent energy deposits in the energy measuring part
of the experiment. OK, we’re done, come on. Aha good, I can’t see
we get past this one. Ah, very good.
Now, if two quarks inside hit very hard, you can have so much energy that
you can produce something really interesting. Here I show for instance a diagram
of two quarks interacting, forming a very energetic gluon
and then decaying to top quarks. Now, you’ve not seen
these kind of diagrams before, but if I showed you
the masses involved, it’s kinda like throwing
2 ping-pong balls at each other, and having 2 bowling balls come out, as the top quarks
are so much more massive. Let me show you the lead-lead collision,
this is just fun. Now we’re throwing 2 lead atoms
at each other, so you have 400 protons
and neutrons colliding. And that’s what that looks like. So, we often talk about these detectors
as something like a camera. They have about 80 million pixels,
but they’re not ordinary cameras. They take up to 40 million pictures per second,
which is pretty hard to do, and the pictures are three-dimensional
with extremely high precision, one micron level precision. And the detectors at
15 and 31 million pounds each are not very portable. Some of the challenges we have are
that these collisions are very frequent. Right now
there’s about 16 million per second and the things we’re looking for
are really rare. So the Higgs events we’re looking for,
some are 1 in a trillion. So we have to run a long time,
continuously round the clock, many, many collisions
have to be collected. We keep about 1000
of these 16 million every second, and that’s still a lot of data,
in fact. In fact we end up with about 22 petabytes
of data per year, a petabyte, I think is
a million gigabytes, correct? So, there’s a ton of data,
we have to transfer it out all over the world, basically to process it,
because it’s too much, to hold in one place.
So it goes out to 34 countries, about a 100,000 computers
are involved. Alright, so I’m going to show you
the Higgs searches finally. Here is a Higgs event, we think, or a possible candidate,
and what you see, are lots of low energy tracks.
This is debris from the protons breaking up. It’s not very interesting,
but you notice these 2 big red bars, alright? Those are actually 2 photons
coming out sideways; they’re very, very energetic. This is a very rare event
and this is what we look for. The Higgs particle could decay to 2 photons
and they would look something like this. But there are lots of other ways
of making two photons and so you end up
with a background of events that’s very smooth like this. But, if you find an excess in anyone place
at a particular mass value, OK – that’s indication of
a possible new particle. And in fact this little bump
is only a few hundred events, OK – that’s an excess corresponding
to a couple of hundred events, at about 125 GeV – and
it took how many collisions to find it? Well, it took ten to the fifteen. So it took a long time running and a lot of sifting through
the data to find these guys. But this little bump, actually,
really represents a major discovery. Here in ATLAS we see a different kind
of event that we’re looking for, the Higgs can also decay to
two Z particles, I mentioned those before, and they can decay to electrons
as well as muons, and this is an event with 4 electrons. You reconstruct the Z’s and then
you reconstruct what you get from the two Z’s and you find, in fact, lots of things
that you would expect. This is a hard to read display and
has lots of data that matches expectations, but there’s one place
where the data is much above expectation, around 150, 125,
and if you look at CMS on the blown-up scale, we also see
an excess at 125, So these little tell-tale signs, actually, are what tell us
that we have something new and we’ve just begun
to see it emerging. It’s very, very new.
They point to a major discovery. Both experiments see excesses
at the mass of 125, in several different channels.
There are some I didn’t show you. And after very intricate studies
and very careful checks that took us months and 100s
and 100s of people involved, everything held up – we know
this is not something we’ve seen before. Everything is consistent
with what’s expected for the Higgs and the significance statistically
is adequate to claim a discovery. But this is really just the beginning. Here is the cover of the publication with the two results
that came out in July. It’s been 48 years
– I’ve just 2 slides left – since the Standard Model Higgs boson
was predicted. It’s been 20 years to design and build these very complex accelerator
and experiments, the most complex experiments ever built
in the history of physics. It took 3 years to acquire the data and it really took a generation
of intense effort by thousands of physicists, engineers and technicians
to make this all possible. So what’s next? Well, we have to figure out what it is. We’re pretty sure it’s the Higgs,
we’re sure it’s a Higgs, I should say, but we have to study its properties,
because there’s a chance it’s not the simple
standard model Higgs. In which case we have something
of a revolution, which could help us understand
a lot of things. And that could take us
to new frontiers, actually. So stay tuned. (Applause)


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