We’ve been expecting this: the ATLAS and CMS experiments at the Large Hadron Collider [LHC]
are going to be making public shortly have made public the publishable form of their papers (preprints, which one submits to a journal for the purpose of peer review) on the search for the Standard Model Higgs particle (the simplest possible type of Higgs particle.) These papers are based on the preliminary results that we heard about on December 13th, which I discussed in some detail here. Here is a page where you can get all the ATLAS and CMS papers. I’ll report after reading them. There will probably be I see no major changes from December 13th, though there will be are interesting minor ones. That’s because the measurements are very sensitive and precise. [UPDATE 1: The two-photon measurement from CMS includes something new: they separate the small number of events that have two additional jets out from the rest. This subset of the data is sensitive to both the g g –> Higgs and q q –> q q Higgs production processes, and it shows an excess at 124 GeV/c2, consistent with the existence of a Standard Model-like Higgs at that mass.] [UPDATE 2: See below]
Since we last heard from ATLAS and CMS, the experimenters have been working to improve their techniques, with the result that energy and momentum measurements (which are crucial to estimating the mass of any potential Higgs particle, and have to be accurate to 0.5% to 1% for each observed photon, electron or muon) will have been adjusted slightly. Since the results from the two experiments were slightly discrepant, favoring Higgs masses that differed at the 2% level (and each slightly disfavoring a Higgs particle at the mass favored by the other), minor changes could potentially have notable effects on how consistent are the hints at the two experiments with each other. [ UPDATE 2: The updated results do not otherwise seem to reveal anything significantly changed from the Dec. 13th presentations; various numbers have drifted around by a fraction of a GeV in energy, but not enough to change notably the level of concordance or discordance between the two experiments. ATLAS’s observed excess is still clearly higher in energy (about 126 GeV, and apparently a fraction of a GeV higher than in December) than is that of CMS (124, which doesn’t appear to have moved much), especially in the crucial two-photon channel — enough to raise issues about consistency, but not enough to make the results clearly inconsistent, given how little data is as yet available. The statistical significances of the excesses have slightly changed, but by insignificant amounts. So… not much news that I can see so far, except for what I mentioned in UPDATE 1. Will report more if I learn something.]]
It is very easy (and psychologically tempting) to over-interpret small amounts of data, and we must fight that human tendency. We simply need more data, about three or four times as much as we have now, and that’s what we’re hoping the LHC will get in 2012.
We can expect a little more news on the 2011 data set around the time of the Moriond conference (March) perhaps including more results from ATLAS and maybe a combination of the CMS and ATLAS results. But new data? Not before summer, and the large amount of data we’ll need for a much firmer conclusion probably won’t come before fall. In the meanwhile, we’ll keep ourselves busy studying the many new results that will be coming from the searches for new and unexpected phenomena at ATLAS and CMS.