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LHC Homes In On Possible Higgs Boson Around 126GeV
New submitter Ginger Unicorn writes "In a seminar held at CERN today, the ATLAS and CMS experiments presented the status of their searches for the Standard Model Higgs boson. Their results are based on the analysis of considerably more data than those presented at the summer conferences, sufficient to make significant progress in the search for the Higgs boson, but not enough to make any conclusive statement on the existence or non-existence of the elusive Higgs. The main conclusion is that the Standard Model Higgs boson, if it exists, is most likely to have a mass constrained to the range 116-130 GeV by the ATLAS experiment, and 115-127 GeV by CMS. Tantalising hints have been seen by both experiments in this mass region, but these are not yet strong enough to claim a discovery."
The Higgs Boson is holding a press conference at midnight on Dec 24th. He's giving Christmas mass.
I was lucky enough to have a lunch hour where I could see the ATLAS results presentation.
The actual bump on the ATLAS graph was about 126 GeV, and the local sigma was 3.6 which is pretty good. The overall was only 2.4, which IIRC is about 95% certainty. I like the odds of finding it there.
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No that's the point; they can't check all the ranges.
The LHC is incapable of operating at the upper energies of the predicted spectrum of the higgs boson. It simply cannot check all of the places it might be hiding (this was known before construction even started)
As said at http://cms.web.cern.ch/news/cms-search-standard-model-higgs-boson-lhc-data-2010-and-2011, they have excluded 128 – 525 GeV at 99% confidence level. I am not sure they measure higher than 525 GeV with LHC for now. I would expect that existing theories for the Higgs put limits on its mass. Of course theories can be wrong, but if all theories about the Higgs are wrong, then there is no such particle.
Looking for higher mass Higgs is easier than for this 120-ish GeV mass. E.g. if Higgs would be 150-200 GeV it would (via heavy vector bosons, which are 80-90 GeV) decay a lot into electrons and muons which are very easy to detect and see that they come from decay of Higgs. For 120-ish GeV Higgs, it decays mostly into two quarks and this is difficult to see because there are a *lot* of quarks flying around in proton-proton machine. So they have to use decays into two photons, which don't happen so often. Thus they need more time to discover Higgs of 125 GeV, than they would need for the one of 200 GeV.
The fascinating thing about the energy they're talking about (125-126 GeV) is that it's too low. So low, in fact, that the equations predict vacuum instability at about that range.
What does vacuum instability mean? It means that vacuum might have a half-life, after which it decays into energy. This is a cool concept until you realize that the Universe is mostly made of vacuum. If the Universe were to spontaneously disintegrate, that would be Bad.
Of course since that doesn't happen, there must be new physics that keeps everything from fizzling out. That means that if the Higgs boson is found at 126 GeV then we're not done searching. There will be new questions to answer and possibly a new particle, the Higgsino, to look for.
Exciting stuff if you're a physics nerd. Or really for anyone who has a vested interest in the Universe continuing to exist.
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The LHC is incapable of operating at the upper energies of the predicted spectrum of the higgs boson.....(this was known before construction even started)
Sorry but we certainly are capable of probing the ENTIRE allowed mass range for the Standard Model Higgs. The upper bound is ~1 TeV/c2 because at this level, without the Higgs boson, some Standard Model processes e.g. e+e--->W+W- "break unitarity" i.e. have a more than 100% chance of happening. Since this is clearly wrong it means that the Standard Model without a Higgs breaks down. Hence we only have to cover up to 1 TeV/c2 in allowed mass and either we find the Higgs or at least see a clear deviation from the SM and possibly see what causes that deviation.
There are ways to hide the Higgs, so-called "invisible Higgs" models, but these all require physics beyond the Standard Model. Also you can fit the existing SM parameters to find a prediction for the Higgs mass and this indicates that it should be below ~200GeV/c2 with a 95% confidence - although I'd take this with a pinch of salt. Now to get to the high mass range we will certainly need the full LHC energy i.e. 14 TeV. We currently have 7 TeV but this is NOT what the LHC was designed to run at - we are just limited to this energy due to the superconducting power bar problems. So to say that it was known that we cannot reach the upper energies before construction even started is simply wrong - the LHC was specifically designed to cover the entire energy range and, once we reach the design energy, we'll be able to do just that....although it is looking like the Higgs is there just at the low end of the mass range.
Slow news? This could be massive news, but we're not sure yet.