Lift11: Tara Shears, An update on the Large Hadron Collider project [en]

[fr] Notes de la conférence Lift11 à Genève.

Live and India-lagged notes from the Lift11 Conference in Geneva. Might contain errors and personal opinions. Use the comments if you spot nasty errors.

A voyage into the unknown. What do we know, but more importantly, what are we trying to find out?

Particle physics is a study of the universe, from the smallest sub-atomic level upwards, extrapolating to the behaviour of the universe. Recreate the conditions in which the universe came to life in a lab: LHC.

Twelve fundamental particles. Held together by the weak force, electromagnetic force, strong force — that one holds atomic nuclei together.

Basically it for particle physics, but not all there is for the universe. Oh, gravity!

Standard model for particle physics: haven’t yet found an experiment that contradicts it, but it doesn’t include gravity and some other stuff, so we’re set for a fall.


What is mass? not predicted by the theory. Higgs’ theory tries to explain that particles gain mass by interaction with another type of particle (“Higgs particle” which we have never managed to see — worrying). Problem: if we can’t find the Higgs particle, it means the Standard model is wrong, oups. Back to the drawing board.

Second problem: antimatter. We don’t see it. We know it was created, but…? Matter and antimatter annihilation went on a lot during the first minute after the big bag, but then…? The matter that composes the universe is just a tiny little difference between the matter and anti-matter that was there. Why the difference?

Third: what about the other 96% of the universe that we haven’t studied and can’t see — dark matter and dark energy.

Gosh, how do we make progress? We make experiments.

Cern: experiment physicists from all over the world.

The LHC occupies a circle 27km in diameter, probably the biggest piece of interconnected scientific equipment in the world. Lots of magnets. Slight curvature because the tunnel is so big.

Accelerate 2 proton beams at 20 km/h less (?) than the speed of light. Lots of collisions, snapshots, recreating conditions at the onset of time. LHC is the most powerful particle accelerator ever built, so it enables us to look back at such early times as was never done before.

But is it working? Since last March, has been working very well. Half-design energy. Started off at very low energy, slowly ramping up energy.

First results start with snapshots. Understand where the standard model breaks down. Quarks: standard model holds. Holds disgustingly for all the forces. Looks good so far, but need more data.

Looking for the Higgs, but not enough data — working out how much more data they need to either rule out the Higgs or see the first hint of its existence. Probably by the end of next year: should be able to tell us whether the Higgs exists… or not. Very exciting time!

What about the unexpected? The unknown unknowns? Search for dark matter, extra dimensions of space and time, evidence of strings (?)…

Black holes? First thing they looked for, embarrassingly, but didn’t found any. None that they can think of!

Unexpected: possible new phase of matter. Distribution of particles which seemed to know each other, non-random distribution. But it’s completely new and they don’t understand it, still analyzing.

Latest news about antimatter: we don’t yet have enough data to really pin down antimatter, but results in the past year from the Alpha experiment. Trapped a sample of antimatter and hold it for a reasonable of time. 38 anti-H atoms for 0.18 seconds. Never isolated before! We can actually look at them!

Very exciting to have this new facility which is allowing big steps forward in understanding the universe — things are moving really fast! Expect interesting results to come out… but we have no clue what! *steph-note: this is the kind of thing that made me want to study physics when I was a teenager :-)*