The LHC In A Nutshell

During the planning of the Large Hadron Collider (LHC) Wide Angle, Discovery News Editor-in-Chief Lori Cuthbert had some questions about LHC physics for Space Producer Ian O'Neill. In this entertaining IM Interview, Lori quizzes Ian about how the LHC works, whether micro-black holes have much "suck" and if particles in checked jackets will make an appearance in Switzerland at the European Organization for Nuclear Research -- or CERN -- where the LHC lives.

Lori Cuthbert: What is the Large Hadron Collider?

Ian O'Neill: The LHC is the most advanced and most powerful particle accelerator on the planet... it's even more complex than the space station.

Lori Cuthbert: So, it's a machine that makes particles go faster than they otherwise do?

Ian O'Neill: Exactly. Your basic particle accelerator can accelerate charged particles to very, very high velocities. Particle accelerators do this using very powerful electric fields.

Lori Cuthbert: How does that work?

Ian O'Neill: The best analogy I have is if you imagine basically a very long gun barrel, where particles are 'injected' into one end and they are fired down the barrel.

The particles move because they are charged, and when dropped into a massively powerful electric field, they move. Very powerful magnets (electromagnets) are then used to control the particle's direction.

So if you have a series of these powerful electromagnets, all controlling these particles as they fly down the tunnel, they can be accelerated to relativistic speeds.

Lori Cuthbert: Reminds me of jai lai somehow, like a series of jai lai players winging the particles down a tunnel.

Ian O'Neill: At the end of the tunnel there's a "target" that these speedy particles slam into.

Lori Cuthbert: Oh! I thought the particles smashed into each other.

Ian O'Neill: Ah! That's where the LHC is even better!

Basically, the linear accelerators fire particles into stationary targets. However, the LHC (and other ringed particle accelerators) collide particles, which is a crazy-complicated thing to do.

The LHC is a long (17-mile) ring of electromagnets. In fact, there's 1,600 of these electromagnets all working together to control the speeding protons and lead nuclei around the circle. And the best thing is, they are eventually accelerated around this circle 11,000 times per second, so rather than just a sprint and impact (in the linear accelerator), the LHC can speed these particles in circles all day... on each lap speeding them up a little bit.

And now comes the clever part of it. The LHC accelerates two "beams" of particles; one going clockwise and one going counterclockwise. And at strategic points around the 17 mile ring, the extremely powerful magnets can be commanded to cross these beams. This is when the fireworks begin!

Lori Cuthbert: Where do they get the particles? A particle store?

Ian O'Neill: Kinda... the particles are injected from smaller accelerators -- like a mini-LHCs attached the main ring -- so when the LHC is ready to be switched on, the smaller rings synchronize with the main ring and the particles are injected into the LHC... the race then begins.

The smaller rings gets the particles "up to speed" before the LHC pushes them faster.

Lori Cuthbert: I have an image in my head of a NASCAR race track, with cars whizzing around really fast...

Ian O'Neill: Exactly right!

Lori Cuthbert: ...and then they cross over to the super-fast track, where they're REALLY cranking.

Ian O'Neill: But on each "lap" of the track they get faster.

Lori Cuthbert: OK -- and on the super-fast track, there are cars coming the other way.

Ian O'Neill: Yes, there are two tracks, one with clockwise traffic, the other with counterclockwise traffic.

Lori Cuthbert: Right. And then, when they can't get any faster, the two loops of cars veer into each other and crash. Just in the LHC, it's streams of particles instead of cars. That would be very messy with cars. Is that right?

Ian O'Neill: Yes. The CERN physicists measure how fast the particles are going. If they know their speed, they know the particle's energy. When they reach a certain energy, the electromagnets (that are controlling the behavior of the speeding stream of particles) force the particles to cross.... then they crash... head on...

Lori Cuthbert: And when the two paths cross and crash, what happens? Or is that the whole point -- to see what happens?

Ian O'Neill: Yes, absolutely. Although previous particle accelerators have an idea about what is going to happen, the LHC will perform the most powerful collisions yet. This is where things get interesting.

HUNTING THE HIGGS

Lori Cuthbert: What are the scientists looking for?

Ian O'Neill: When the LHC starts slamming particles at high energy, we start to see energy conditions comparable to that of moments after the Big Bang.

At the moment of the Big Bang... there was a big explosion and it was just energy -- pure energy. It was so energetic that no matter could form.

Lori Cuthbert: Like trying to build a sandcastle on a REALLY windy day?

Ian O'Neill: Pretty much. After a microsecond, the universe started to expand. As it expanded, the energy spread, and cooled, and then started to "condense," or "clump," into the most basic forms of matter.

The LHC is often called the "Big Bang" machine and the connection is that the LHC will produce collisions so energetic that the energy conditions before sub-atomic particles were even born can be reproduced.

Lori Cuthbert: And this is desireable why?

Ian O'Neill: Once these energies are produced, we can have a split-second glimpse as to what happened as this matter was condensing.

Lori Cuthbert: How can we see it? Do they measure the energy released by the collisions?

Ian O'Neill: The higher the energy, the more primordial the "stuff" that can be created. And this is where the Higgs particle comes in!

Lori Cuthbert: Something is created besides energy? An actual thing?

Ian O'Neill: Well, the Higgs is technically an "exchange particle" (known as a "boson" in quantum-speak), but it has a very large mass and therefore energy (in quantum terms).

So you need very high-energy collisions to create a "free" Higgs particle

Lori Cuthbert: Does the collision make something stick to the initial particle? Oh! Is the Higgs boson sticky? Do they think that's the universe's glue particle or something?

Ian O'Neill: The Higgs particle carries the "Higgs field" and the Higgs field permeates the entire universe (it has to, otherwise nothing would have "mass"). So as something moves through the Higgs field (i.e. everything), it collects mass.

It's a complex relationship, but I always envision that if something is big and slow, it collects more of the Higgs field. Whereas small and fast things have very little mass.

Lori Cuthbert: Ergo, Higgs particles must permeate the universe too. Since each particle carries a field -- is that right?

Ian O'Neill: Yes, each Higgs particle carries a little bit of the Higgs field.

Lori Cuthbert: Is the Higgs particle what holds the universe together?

Ian O'Neill: The Higgs field gives everything mass. And this mass then has a gravitational field, which in turn holds the universe together.

So the Higgs MUST exist to explain how our universe works.... BUT we might be wrong.

Lori Cuthbert: And they're trying to recreate the Big Bang to see if it's right.

Ian O'Neill: They are trying to recreate the CONDITIONS of the big bang... like a Big Bang mini-sample.

BLACK HOLES: ALARMING?

Lori Cuthbert: Let's talk about the black hole scenario.

Ian O'Neill: Yey! Black holes! I love the thought that we might see the first man-made black holes.

Lori Cuthbert: At what point in the process might a black hole be created?

Ian O'Neill: This is very cool. At the point when the counter-rotating particles collide in the LHC, the signature of a micro-black hole might be seen. It's not guaranteed, but it could be possible.

Lori Cuthbert: That sounds alarming. Can you explain why it's not?

Ian O'Neill: In the collision events, where massive energies are released, and the point where we are looking out for the Higgs particle, physicists may notice that there is "missing" energy.

This "missing" energy could have been carried away by a micro-black hole. Micro black holes aren't scary as they are ridiculously tiny.

Lori Cuthbert: Don't they have incredible sucking power? And, don't all black holes start out tiny?

Ian O'Neill: Stellar-mass black holes are scary as they contain the mass of a star -- they therefore have a massive gravitational pull.

Lori Cuthbert: I see. Tiny black hole, not much sucking power.

Ian O'Neill: These micro-black holes aren't scary as their mass is so small they have virtually zero gravitational influence on matter. So no sucking power at all.

If they bump into a tiny particle, that particle might be sucked in, but that's it. Black holes need lots of food, especially when they are small.

Therefore, micro black holes can't survive for more than an instant -- they fizzle out of existence instantly.

After the collision, physicists will look at their data and find a cascade of new particles created. And although billions of particles are in the colliding beams, only a tiny fraction of these particles actually collide.

Lori Cuthbert: I see.

Ian O'Neill: So there are a lot of unused protons still circulating in the LHC.

Lori Cuthbert: Couldn't the tiny black hole start feeding on those billions of particles? If they're just there like a big buffet?

Ian O'Neill: No, everything is moving too fast. It's like everyone is running through the buffet at light speed, they won't be able to even grab a chicken leg.

Lori Cuthbert: Hehe.

HIGGS BOSON INCOGNITO

Lori Cuthbert: How will they recognize a Higgs particle?

Ian O'Neill: The detectors in the LHC are vastly complex pieces of kit. They are huge too. Their aim is to detect as many particles as possible after the collision event.

Lori Cuthbert: Is it like each particle has a different color coat on, and suddenly there's a guy with a patchwork coat there that wasn't before?

Ian O'Neill: Yes. It would be exciting if something happens in the collision that should be "impossible." Then it's up to physics to understand why it isn't possible.

The Higgs is predicted to have a certain energy, so I *think* they will basically compare the before and after energies and see what is missing. Also, the Higgs is predicted to "decay" into other particles shortly after it is created. So if these decayed particles pop out of thin air, there's a fairly good chance a Higgs was formed in between.

Lori Cuthbert: You mentioned that they might be wrong. What else might happen instead?

Ian O'Neill: Absolutely. The "Standard Model" (i.e. our most basic understanding of the quantum world) might be flawed, and it might not work at very high energies.

Lori Cuthbert: They must feel pretty sure to have spent all these millions on a collider.

Ian O'Neill: If the Higgs isn't found, this means the final piece of the Standard Model puzzle doesn't fit.

Disproving the Higgs would be just (if not moreso) as important as finding the Higgs. If the Higgs isn't found, we will have a revolution in physics.

If the Higgs is found, we will find out that our understanding of the Universe is validated... which is cool too... but not as cool as a physics revolution.

THE SLOW-MOTION RECAP

Lori Cuthbert: Just to solidify this whole thing, can we go through it in super slo-mo?

Ian O'Neill: OK.

Lori Cuthbert: The particles are zooming in opposite directions around the collider, faster and faster and faster, until they're slammed into each other when it's thought they're going fast enough. KaBAM!

Ian O'Neill: Yes.

Lori Cuthbert: Particles flying everywhere -- the known particles that were originally in the collider. And maybe in the resulting chaos there's another particle present that wasn't there before -- the one in the checked jacket.

Ian O'Neill: True.

Lori Cuthbert: That may or may not be a Higgs particle. And a tiny, harmless, short-lived black hole may or may not be detected.

Ian O'Neill: Absolutely.

Lori Cuthbert: How will they know it's a Higgs particle if they've never detected one? After all, it won't announce itself, or wear a name tag.

Ian O'Neill: Actually, it kinda does have a name tag. Theory predicts it will have a certain energy... also theory predicts it will decay in a certain way. We can detect the decay particles, and if we do (and it is confirmed several times), we'll know a Higgs was generated. So it's almost like the Higgs callsign we're looking out for.

Lori Cuthbert: Oh, cool! Thanks for explaining this to a rookie.

Ian O'Neill: Did it make sense? The LHC is a notoriously difficult thing to fathom. It's taken yonks for me to wrap my brain around it and I'm still only just scratching the surface.

Lori Cuthbert: I think so.