Rumor Mill: Another Anomaly Bites The Dust?

One of the big experimental results that seemed to contradict the Standard Model was the "like sign dimuon asymmetry" observed at an almost 4 sigma level by the D0 experiment at Tevatron starting about four years ago, most likely due to CP violations beyond the predicted amounts in B meson decays.

Rumor has it, however, that LHCb, which is running an experiment to see if it can confirm this observation from Tevatron has seen no deviations from the Standard Model predictions, and more particularly, no like sign dimuon asymmetry. The rumors at a leading physics blog, in particular, were that:

chris said...
just last week i heard from an LHCb guy that they are desperately looking for new ideas of where to look for deviations from the SM. he explicitly said that they are frustrated by not seeing any hint of new physics at all.

23 August 2011 09:26 . . .

Anonymous said...
I also heard from an LHCb guy that they are seeing no deviation in the like sign dimuon asymmetry, completely contradicting D0.

23 August 2011 19:36

The results may be announced at Lepton-Photon in Mumbai on Saturday. We could, of course, simply wait to see what they actually say, but where would be the fun in that?

If the rumored LHCb result is accurate (and it wouldn't be the first time that a D0 experimental indication didn't pan out when attempts were made to confirm it), the motivation to devise beyond the Standard Model particle physics would be greatly reduced, although it isn't clear to me how many different ways there is experimental evidence for beyond the Standard Model CP violation in B meson decay, of which this may be only one example. Still the discounting of this result takes some strain off apparent experimental indications that the CKM matrix is broken, in the sense that no set of entries in this matrix that describes the probability that quarks of one generation turn into quarks of a different generation via the weak force in a way consistent with experiment within the margins of error in those experiments. The high levels of CP violation in B meson decay relative to Standard Model prediction are the main reason that the CKM matrix is out of whack, and if LHCb establishes that those decays aren't as CP violating as this D0 experiment had indicated, then it is much easier to fit all of the remaining experimental data to a single theoretical set of CKM matrix entries that can describe all of the experimental data.

This is one of several experimental results that are on the short list of physics blogger Jester that could contest the Standard Model, and have been seriously called into question in the last few months.

Indeed, in general, LHC has yet to find any compelling evidence of Beyond the Standard Model physics, and it has not ruled out a low mass (114 GeV to 130 GeV) Standard Model Higgs boson, as this is the mass range where the LHC experiment is least sensitive and thus requires the most data to produce a definitive result.

In my mind the most compelling experimental evidence that seems to be an ill fit for the Standard Model is the measured muonic hydrogen atom size, which is notable for the size of the difference and the accuracy of the theoretical expectation, and which is also notable for not being predicted by almost anybody.

Updated August 28, 2011:

Quantum Diaries Survivor tends to confirm the rumors:

[T]he recent searches for Supersymmetry by ATLAS and CMS, now analyzing datasets that by all standards must be considered "a heck of a lot of data", have returned negative results and have placed lower limits on sparticle masses at values much larger than those previously investigated (by experiments at the Tevatron and LEP II).

Similar is the tune being sung on the B-physics sector, now being probed with unprecedented accuracy by the dedicated LHCb experiment (along with again precise measurements by ATLAS and CMS, plus of course the Tevatron experiments). I have not reported on those results here yet, but will duly do so in the next weeks. In a nutshell, anyway, deviations from the Standard Model predictions are all well within one sigma or two; the hypothetical contribution of SUSY particles in virtual loops taking part in the decay of B hadrons must be very small in order to fit in this picture.