Higgs excitement

[e_pepys]

Today was an exciting day. Finally we can see our our new Higgs search results public, and we can see what CMS have seen and compare. As everyone keeps emphasising, we haven't discovered the Higgs. ATLAS has seen a fairly large "excess" and CMS have a couple of moderate excesses, one of which matches ours at a mass of 126 GeV

Comments

[parrot_knight]

Fascinating - but what does GeV stand for, and why measure probability in 'sigma'?

[e_pepys]

Sorry for the jargon. I sort of forget what is jargon, but also want to give a flavour of what we are talking about without converting to millions and millions.

GeV stands for "giga electron volts", but its just a convenient unit for particle masses (actually it's a unit of energy, but E=mc2 and all that - if I were being formal, I'd say "GeV/c2"). For scale, a proton has a mass of about 1 GeV.

"sigma" is a measure of probability that doesn't need many zeros for small values (eg. 5 sigma is a probability of 3x10-7). It is also convenient for combining probabilities (like I certainly wouldn't do with ATLAS and CMS results) and estimating fluctuations. "1 sigma", "2 sigma", etc have also become common benchmarks in measuring significances.

(Formally "sigma" is the symbol for the "standard deviation" measure of the width of a Normal distribution (bell curve). Many of the probabilities are distributed like that (in fact part of my job was to check this for our measurements), but equivalent Normal sigmas have come to be used regardless

[e_pepys]

Oh look, CMS used "GeV/c2" on the axis of their plot, while we just said "GeV". Maybe we should fix that informality in the paper!

[zengineer]

It looks like the experiments are seeing something

[e_pepys]

Good points. You honed in on some of the crucial questions

[zengineer]

Thanks. I get some explanation at work but generally it either assumes you are already working at CERN as a particle physicist or you work in the finance office without much in between.