Friday, 29 June 2012

H-day -5: heaven or hell?

In about 125 hours ATLAS and CMS will present new results of the Higgs searches,  including about 5fb-1 of data collected at 8 TeV energy in 2012. If you read blogs you know that a fireworks display is promised on the 4th of July. It is not clear, at least to me, if either of the 2 experiments will pass the 5 sigma fetish. But it does not really matter. The 2011 data were already showing a solid evidence of a Higgs-like particle with the mass near 125 GeV and decaying to photons. What's going to change next Wednesday is that the status of the Higgs will be upgraded from "almost certain" to "beyond reasonable doubt".   

Generally speaking, the Higgs searches at the LHC could unfold according to one of the following three scenarios:
  • Experimentalist's hell: no Higgs is found at the LHC. The experimentalists feel awkward, politicians ask difficult question, the public suggests to check for loose cables. Meanwhile, theorists spam the arXiv with countless Higgsless, invisible Higgs, unHiggs, or buried Higgs models.   Since last December this scenario has become very unlikely. 
  • Theorist's hell: Higgs is discovered, perfectly matching the predictions of the Standard Model. The public cheers, everyone pats experimentalists on the backs, Gary Taubes writes "Nobel Dreams II".   A few years later, the last particle theorist leaves his office, switches off the light, and returns the key. 
  • Heaven for all: Higgs is discovered, but it's different than the one predicted by the Standard Model.  This is the best of all worlds, where the measured Higgs properties clearly point to the existence of other, yet unknown particles within the reach of the LHC.  For the rest of the century theorists and experimentalists work hand in hand to pinpoint the true theory of fundamental interactions at the weak scale.  
Which of the last 2 scenarios is true will not be decided on the 4th of July, but the odds may be affected.  

To wrap up, although the general public expects binary answer: Higgs or not Higgs, 5 sigma or less, Italy or Spain, etc, the stakes are somewhat different for particle physicists. Most of the theorists have already answered yes to the Higgs questions; now the most pressing issue is whether the resonance observed at the LHC is the Standard Model Higgs or not. Intriguingly, the 2011 Higgs data were showing hints of something interesting going on: a somewhat too large rate in the Higgs-to-diphoton channel, and a deficit of events in the WW channel. The 4th of July may clarify whether these were simply statistical fluctuations, or whether the hints persist in the new data.  It would be ironic if the day of the greatest triumph of the Standard Model were also the beginning of its collapse...

8 comments:

Anonymous said...

Will there be a webcast? Would very much appreciate a link. Should it happen to be scenario II (God forbid) it may be the particle physics event of a century ;)

Jester said...

yes, there will be a webcast here: http://webcast.web.cern.ch/webcast/

Anonymous said...

I fear the rest of 2012 will be spent in the unpleasant intermediate scenario: higgs-like beyond reasonable doubt, but still far from having hints of whether the thing is a hideous fundamental scalar or not. maybe we shouldn't check hep-ph until after moriond 2013...

Heather Logan said...

Hang on, I thought the greatest triumph of the Standard Model was the LEP Z-pole measurements? ;)

Jester said...

I wasn't born yet so it doesn't count ;-) In any case, the triumph is when you finish the entire puzzle.

Torbjörn Larsson, OM said...

80 % of the matter we see is largely uncharacterized, and theorists are hanging up their hats? Or what about neutrinos, if DM is too vague (but why?) to get a decent handle on?

It's a large universe out there. I think Jester was jesting.

Jester said...

Sure, I was taunting a bit, whatever happens particle theory won't vanish that quickly. But it does not change the fact that, if the LHC finds nothing but the SM Higgs, our prospects look bleak.

slammed said...

I just found this blog in time. I hope to be able to listen to the webcast. The Higgs particle would be the discovery of the 21st Century and just think how much fun it will be sorting everything out.