Sunday, August 28, 2011

LHCb establishes that there is no B meson anomaly

One of the strongest signs to date of beyond the standard model physics has been experimental data not consistent with the Standard Model prediction in the decay of B mesons.

For example, these showed stronger CP symmetry violation that previous Standard Model CP symmetry violating phases derived from neutral kaon decay (a kaon is a type of meson with a strange quark in it) had predicted. The Tevatron data, had it held up, would appear to break the CKM matrix and require two CP violating phases rather than just one to fit the data.

But, the LHCb data contradicts the Tevatron data and confirms the Standard Model prediction on this score and thus elminates the need to develop a beyond the standard model theory to explain the data. As Jester explains at Resonaances:

This result is extremely disappointing. Not only LHCb failed to see any trace of new physics, but they also put a big question mark on the D0 observation of the anomalous di-muon charge asymmetry. Indeed, as can be seen from the plot on the right, the latter result could be explained by a negative phase φs of order -0.7, which is now strongly disfavored. In the present situation the most likely hypothesis is that the DZero result is wrong, although theorists will certainly construct models where both results can be made compatible. All in all, it was another disconcerting day for our hopes of finding new physics at the LHC. On the positive side, we won't have to learn B-physics after all ;-)

Meanwhile, Lubos is steaming angry that the press is reporting that SUSY is near dead when he thinks that there are lots of ways for it to remain alive and kicking.

At this point, the only piece of the Standard Model which has not yet come together experimentally is the detection of a Higgs boson, but there isn't enough data yet to rule out its existence in the 115 GeV to 130 GeV range or even make very good predictions in this mass range, even with 2 inverse femtobarns of data collected.

The B meson data also destroys much of the experimental motivation, for example, for a fourth generation of Standard Model fermions (the SM4).

Those hoping for new physics need not despair unduly, however. Without a light Higgs boson discovery, the Standard Model "blows up" and ceases to make coherent theoretical predictions in the 1 TeV to 10 TeV range. So, either the Higgs boson will be discovered (which is still something new even if it has been predicted), or we will get new physics as a result of it not existing whatever happens at 1 TeV to 10 TeV as the experimental results, whatever they may be, will surely not be indeterminate.


Maju said...

"Those hoping for new physics need not despair"...

I understand that "new" physics are needed even with the standard model because this one so far has been unable to explain anything at all regarding gravity. It is the fusion of quantum mechanics and relativity what needs new physics rather than any (quite elusive) failure of the standard model of QM.

Andrew Oh-Willeke said...

True enough. But, in context, "hoping for new physics" means hoping for experiments that contradict of the Standard Model or General Relativity that need to be explained by some new theory.

The inconsistencies between the two grand theories of fundamental physics are exist in principle, but no one has ever done an experiment that has showed an inaccuracy in either one.

Maju said...

I did not know there was people hoping for that, trying to break down a scientific paradigm that has withstood a whole century. It can be improved but hardly demolished, same as Newtonian physics were never destroyed but overwhelmed by genuine new physics and eventually declared obsolete at least for some fields and applications.