Europe by Physics and Train

This post is now also on The Guardian. See also Chapter 3.5 of Smashing Physics.

Back in Geneva after the SUSY meeting in Bonn and a day in the mountains.

In the mountains

One of us is not talking physics

The return journey wasn’t as pleasant as the outward one. The train didn’t turn up at Bonn Hauptbahnhof so we were taxied across town. This meant a 30min delay and I missed both the next connections. However, via Mannheim, Basel and Bern, I made it in the end*.

The SUSY meeting made it on to German TV in a report starring Herbi Dreiner but briefly featuring me listening to my own talk, thanks to some nifty editing**. As far as I can tell with my poor German language skills the report looks fun & informative – good when physics is news. Herbi is a bit of a “science in public” star anyway, having won the European Physical Society prize last year for his physics show, something I hope he gets to perform in the UK soon.

ATLAS Luminosity

I can’t really give an account of the meeting because I could only be there for one day. But even on that day you could see the change of mood now people are finally showing LHC data rather than simulations. So far the data don’t break new ground in SUSY, but it won’t be long at this rate. The plot shows the amount of data collected by ATLAS from LHC collisions. Not only is it increasing, but the rate of increase is increasing. When we have about 50pb-1*** we will be passing the Tevatron in the search for SUSY. By this time next year we expect to have about 1000pb-1. (Today we have three…)

I said I might give an argument as to whether or not supersymmetry “looks nice” (apart from the Higgs mass and Dark Matter arguments I gave earlier).

Briefly my take on it is that it introduces a symmetry between the force-carrying particles (photon, W, Z, gluon) and the others (quarks and leptons). Symmetries in nature general make things look more compact and natural.

Unfortunately, if SUSY is going to solve the Dark Matter problem and the Higgs mass problem, it has to be a broken symmetry, because otherwise all the SUSY particles would have the same mass as the Standard Model particles. And they don’t, or we would have seen the SUSY particles already. Plus SUSY does not explain why all the Standard Model particles have the particular values of mass that they have. So it introduces lots more arbitrary parameters into the theory (to do with the masses of the SUSY particles, how they mix up, and how supersymmetry is broken). This is why it is so “flexible” as I described before, but it also makes it less predictive and less aesthetically pleasing. Or “nice”.

Herbi couldn’t remember whether it was a napkin or not. But he is better qualified than me to explain the good bits about SUSY (the theory, not the conference), and will do so shortly I hope.

* And despite this delay I am still a fan of Deutsche Bahn, especially their website which is the only way I know to sensibly book European rail journeys (even outside Germany).

** Any diehard fans can find a video of the almost identical talk I gave in Paris here (Friday session). The idea behind it is essentially the idea behind this.

*** That’s inverse picobarns, a unit I will not expain here. Yet.



About Jon Butterworth

UCL Physics Prof working on LHC, dad, dodgy guitarist, Man City fan in exile.
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