Just got back from vacation this morning. Luckily I managed to be away for the blogosphere-fueled Higgs rumors, returned just in time to catch the released results which appeared in a Fermilab press release minutes ago. The ICHEP talk in Paris announcing these results will start in about half an hour, slides should appear here.
The bottom line is that CDF and D0 can now exclude (at 95% confidence level) the existence of a Standard Model Higgs particle over a fairly wide mass range in the higher mass part of the expected region: from 158 to 175 GeV. If the SM Higgs exists, it appears highly likely that it is in the region between 114 GeV (the LEP limit) and 158 GeV. The most relevant graph is here. It shows an excess of about 1 sigma over the entire region 125 GeV to 150 GeV, which unfortunately is nothing more than the barest possible hint of something actually being there.
Why is there a difference between “expected” and “SM=1” in the linked graph?
On a different topic, one thing I’d have expected you to comment about is the recent “finding” that the proton’s charge radius appears different from that predicted by QED.
http://en.wikipedia.org/wiki/Proton#Charge_Radius
Presumably either the proton’s charge radius is described by something other than current QED model, or the mathematical model used to infer the charge radius from a proton+meson is wrong, both of which look like new clues about some issue in the area of field theories that you’re interested in. Any thoughts?
WCG,
The experiments are not seeing a signal, so the plot is of the 95% confidence level limit they can put on a signal/divided by the signal expected for a SM Higgs. The “expected” value for this is based on the expected performance of the detectors. Around 165 GeV they expect to be able to put a limit on the size of the signal below the SM value, and they do, ruling out the existence of a Higgs at that mass. Around 125 GeV they expect to only be able to get a limit about 1.8 times the SM value, so don’t expect to be able to rule out a Higgs at that mass.
If there really were a Higgs at a certain mass, one expects that the experiments would start to see an excess above expected background, and this would make their 95% confidence level worse than expected. However, the excess they are seeing is still so small as to be quite consistent with no real signal.
bane,
That’s on a list of things to learn more about and see if there’s anything interesting to say. But I just got back from vacation a few hours ago….
Update: for those who really want to discuss the proton charge radius question, this really isn’t the place.
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The q^2 employed in the old proton charge radius measurements is probably of order 1 GeV^2, while the new muonic hydrogen measurements probably have a q^2 of order the muon mass squared, or 0.01 GeV^2.
Would it be very surprising if QCD caused evolution of the charge radius between those values of q^2?
As for the Higgs, someday I’d like to dig out all the august testimony to Congress during the SSC days, where the leading figures of the field argued passionately for the SSC’s energy and luminosity, in order to test the Higgs hypothesis sufficiently.
The LHC was not sufficient, they said. Of course a bunch of blurry estimates of the Higgs mass happened between then and now, and have pointed at the light Higgs and thus new physics soon. But maybe it was all Luck not being a Lady, and instead, we have a 800 GeV Higgs + some strongly interacting electroweak bosons, and now trace of new physics, and thus a desert.
I just watched Veltman’s video presentation about the Higgs at the Lindau Confererence here:
http://www.lindau-nobel.org/WebHome.AxCMS
I thought it was an excellent presentation that gives a jargon free explanation of the search for the Higgs. It really is an outstanding talk and I came away with a much better understanding of the issues involved. I’m still digesting his final conclusion about why he thinks there is no Higgs. I’ll give a hint: It involves the corrections to the scattering amplitudes of the vector bosons that would require a Higgs particle. Second hint: the highest sigma for the Higgs is at one particular energy where there is no scattering correction required. I think he is onto something. I like the guy.
Eric Habegger
Veltman has disbelieved in the Higgs since the beginning. (This despite the proof of renormalizability of Yang-Mills with SSB etc.) But does he offer any credible alternative for the gauge boson mass and their longitudinal polarization modes?