So, no Higgs yet!

Hey! There it is! ... What? What did you say? It's just simulation?

I am one of these contrarians who is actually rooting against the existence of the Higgs boson. I was becoming quite anxious in the last week or so as I started hearing rumours of strong excesses found in the Higgs search. Only rumours after all, to my bewildered relief. Actually, my position on the Higgs is more complicated than “I think it doesn’t exist”, but is also quite irrelevant for what matters, and that’s not what you must be interested in right now.

By the way, Peter Higgs, the guy after who the famous boson is named, now has a hilarious middle name.

ATLAS was the first to present its results, after a pretty good talk outlining the Standard Model Higgs theory. ATLAS presented results from Higgs searches in 8 different channels for the Standard Model Higgs, and two channels for the Minimally Supersymmetric Standard Model (abbreviated as MSSM; I may explain what this one is at some point on this blog, it is quite interesting). If you remember from the previous post, ATLAS was seeing a bit of an excess in the WW channel. The Lepton-Photon result has 1.7 times more data and the excess is still there, but it recessed a little bit. All the other channels don’t see anything. I was excited to see that the ZZ channel is now giving results. The ZZ channel is the one in which we find the “golden mode”, in which each Z decays to a pair of muons. This channel has so few types of events that can produce the same signature that if it is ever seen in the detector, even if it is only one event, it will provoke huge excitement.

The good news is that the exclusion ranges have been extended quite a bit. There are now 3 separate ranges. We can now be sure with 95% confidence that the Higgs cannot be in the following mass ranges: 146-232 GeV, 256-282 GeV and 296-466 GeV. We are closing in on a regime where we will be talking about the “Higgs of the gaps”! Nothing has been seen for the MSSM Higgs either, and the Supersymmetry parameter space is being further constrained.

CMS has very similar results to put forward, except that they are now seeing an excess too in the WW channel, in about the same mass range, that is between 115 and 145 GeV. They have started looking into the ZZ channel as well, and they have excluded the following mass ranges: 145-216 GeV, 226-288 GeV and 310-400 GeV. Nothing for the MSSM Higgs either.

Finally, results from the Tevatron were shown, and this is the part that I found the most intriguing. First, remember that post I made about CDF potentially seeing a new particle? Well, the excess they saw has gone up to 4.1 sigma. D0 still doesn’t see it. If it is real, a potential Standard Model explanation has been found, concerning high-order effects from the strong interaction.

But even more weird is that both Tevatron experiments see an excess in their Higgs searches between 120-150 GeV, exactly where ATLAS and CMS see their own excesses. 4 experiments seeing an excess at the same place is much more of a tantalizing hint than only one experiment seeing it. Unless they are all using the same faulty way of modelling their backgrounds, it seems quite worth worrying about. The thing is, all 4 experiments see a small excess. Since combination results are not ready yet, there is no way to know if that is really significant. I don’t know how this is going to play out, but it is certainly exciting to follow. I am becoming anxious again…

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