Search for the Rare Decays Bs(d) → &mu+&mu-

Primary authors: D. Glenzinski, M. Herndon, T. Kamon, V. Krutelyov, J. Naganoma, D. Sperka , L. Sartori ,F. Scuri, G. Volpi

This page summarizes an analysis which searches for the rare decays Bs → μμ and Bd → μμ . These results were finalized on August 13th, 2009 and use a dataset of 3.7 fb-1.
This analysis supersedes the analyses performed with 2 fb-1 PRL 100,101802 (2008) (webpage), 365 pb-1 PRL 95, 221805 2005 (webpage) and 171pb-1 PRL 93, 032001 2004 (webpage).


The technique used in this analysis is identical to that described in PRL 100,101802 (2008). The dataset is updated to include a total of 3.7 fb-1 and additional di-muon trigger acceptance. The analysis is discussed in detail in CDF public note 9892.


Searches for the decays Bs → μμ and Bd → μμ can be a powerful tool to probe for physics beyond the SM. The SM predicts a BR( Bs → μμ ) of about 3.86x10-9. There are various extensions to the SM that predict an enhancement of this branching ratio by one to three orders of magnitude. Many of these models are, presently, theoretically very interesting since some have some relevance to the deviation of the muon (g-2), neutrino oscillations, Bs oscillations, and dark matter/dark energy results. As of this analysis limits are now approximately one order of magnitude above the predicted SM branching ratio placing significant restrictions on many new physics models.

A recent paper emphasizing the connection between Bs → μμ , Bs oscillations and the direct detection of dark matter can be found at hep-ph/0907.4946.

Result: World's best limits

BR( Bs → μμ ) < 4.3x10-8 @95% CL
BR( Bd → μμ ) < 7.6x10-9 @95% CL

The signal windows (Bs in blue and Bd in red) in 3 NN bins with background fits superimposed.


Below are gif versions of relevant figures available for download. This analysis is divided into two channels for events found using only the central muon system(CMU), events, and events where one muon is found in the forward muon extension(CMX), events.