Rencontres de Moriond EW 2012: Seeing less would be just as good

Seeing less than the value predicted by the Standard Model for rare B decays branching ratios would still open the door to new physics. This is the reassuring message David Straub delivered to a relieved audience yesterday morning at the Moriond conference.


After the LHCb announcement of the most precise measurement to date of the rare decay of Bs to two muons Monday at the Moriond conference, a slight wind of pessimism swept through the audience: everybody had been hoping to see the first signs of new physics revealed by a small excess in the branching ratio predicted by the Standard Model.

But thanks to David Straub’s talk yesterday morning, the sun is shining again. Straub, a theorist affiliated with Scuola Normale Superiore and INFN in Pisa, based on work done with Wolfgang Altmannshofer (FNAL) and Paride Paradisi (CERN) showed that in fact, finding a smaller branching ratio than the one predicted by the Standard Model would be another way to open the door for new physics, a fact that received little attention before but are becoming possible now with the increase in precision.

“LHCb is already probing the region accessible to new models,” said Straub this morning. This means that with the increased precision LHCb will reach with the 2012 data, we could be able to see whether contributions from outside the Standard Model are needed to explain the measured rare branching ratios of Bs and Bd to two muons.

So, although LHCb new result on Bs is ruling out a large area of the parameter space for different models for new physics, the figure below used by David Straub as a conclusion to his talk, shows that all models still stand a chance, although with much less margin.

by Pauline Gagnon