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LHC Homes In On Possible Higgs Boson Around 126GeV 210

Posted by timothy
from the abundance-of-caution dept.
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."
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LHC Homes In On Possible Higgs Boson Around 126GeV

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  • by rubycodez (864176) on Tuesday December 13, 2011 @12:20PM (#38356208)
    the Standard Model become inconsistent with Higgs boson masses above 1.4 TeV, for example nonsensical total probabilities for certain scattering events greater than 100% appear (unitarity is violated)
  • by Anonymous Coward on Tuesday December 13, 2011 @12:22PM (#38356236)

    One way to constrain the upper bound is with theory. The current Standard Model (without the Higgs) predicts that certain processes will start occurring more than 100% of the time at an energy of approximately 1TeV. The Higgs (or some other similar particle) fixes this problem but only if its mass is below a certain value.

  • by Remus Shepherd (32833) <remus@panix.com> on Tuesday December 13, 2011 @01:28PM (#38357062) Homepage

    Metastability might explain inflation. But it also invites the possibility that inflation could kick off again, and the universe could revert to a previous state where things like stars, planets, and life can not exist. That's what people have a problem with, I think.

    Of course, the fact that this hasn't happened is proof that it probably cannot. The question we then need to answer is why not. It's as if God has us all in a gigantic microwave oven, and we're trying to figure out what's keeping him from hitting the 'Start' button...

  • by bill_mcgonigle (4333) * on Tuesday December 13, 2011 @02:03PM (#38357586) Homepage Journal

    The actual bump on the ATLAS graph was about 126 GeV, and the local sigma was 3.6 which is pretty good

    This model of everything [arxiv.org] predicted a Higgs at 125.992, which is pretty close (with the current error bars). Could be coincidence, of course, but their idea of a well-defined set of rules that predicts each particle's mass correctly is tantalizing.

  • Re:Yes we can! (Score:4, Interesting)

    by hweimer (709734) on Tuesday December 13, 2011 @04:10PM (#38359946) Homepage

    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.

    I somehow never got this point. In the standard model, you're starting from a Lagrangian formulation of a quantum field theory, so the existence of a scalar product in the Hilbert space spanned by the theory automatically guarantees normalization of probabilities, no matter which physical values you attach to the parameters of your model. So if you're getting something larger than one, you must have made an error somewhere on the way, but that doesn't imply your entire model is wrong.

  • Re:Yes we can! (Score:4, Interesting)

    by Roger W Moore (538166) on Tuesday December 13, 2011 @07:34PM (#38363596) Journal
    If you assume no Higgs then you end up with a Lagrangian without any mass terms (because if you put those in you break the local gauge symmetries). However when you do the calculation of e.g. e+e- --> W+W- you have to use the fact that the electron has a mass in the Feynman calculation. This non-zero mass causes you you have a "left over" term which does not cancel in the high energy limit and causes you to break unitarity.

    The Higgs mechanism gets around this by adding a new diagram e+e- --> H --> W+W- which precisely cancels the electron mass term. The reason the cancellation is perfect is because the electron gets its mass from coupling to the non-zero Higgs vacuum expectation value.

    So effectively you are correct in that the reason the model fails at high energy is because you use the electron mass in the cross-section calculation but have no electron mass term in the Lagrangian so you are not being consistent....but you cannot simply stick a mass term in there without adding symmetry breaking interactions which are not observed in nature. Hence you have to add a Higgs field with a non-zero vacuum expectation value which in turn adds more than just the effective mass terms.

    Hope that is comprehensible - it is hard to explain in just typed text!

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