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

This page summarizes an analysis which searches for the rare decays Bs → μμ and Bd → μμ . These results were finalized on April 7th, 2005 and correspond to a dataset of 364 pb-1. A PRL paper on the analysis can be found at hep-ex/0508036.


The SM predicts a BR( Bs → μμ ) of about 3.8x10-9, while the best current limit was:
D0 Run 2, BR( Bs → μμ ) < 3.5x10-7 @95% CL (D0-Note 4733-Conf, Preliminary).

There are various extensions to the SM predict an enhancement of this branching ratio by 1 to 3 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, and dark matter/dark energy results.

Here's a plot from (hep-ph/0108037), which shows BR( Bs → μμ ) in the (M0,M1/2) plane in the MSuGra model. The solid black lines are contours of constant BR( Bs → μμ ), the dotted green lines are contours of constant deviations of the muon (g-2) (in units of E-10) relative to SM expectations and the dash-dot red lines are contours of constant (lowest-lying) higgs mass in this model (in units of GeV). The shaded red-regions are excluded.

A second interesting class of models that predicts enhanced rates of Bs → μμ decay are SO(10) symmetry breaking models. This plot from (hep-ph/0304101) shows BR(Bs->&mu&mu) in the (&mu,M1/2) plane. Dashed blue lines are are contours of constant BR( Bs → μμ ), dashed black lines are are contours of constant higgs mass, green areas are regions of parameter space consistent with the observed relic density of dark matter and pink ares are excluded. This model with the choice of parameters shown in the plot is disfavored. A listing of relevant theory papers is below.


A complete description of the analysis is available here: pdf. The final version published in PRL is here: hep-ex/0508036

Result: World's best limits

BR( Bs → μμ ) < 2.0x10-7 @95% CL
BR( Bd → μμ ) < 5.1x10-8 @95% CL

BR( Bs → μμ ) < 1.5x10-7 @90% CL
BR( Bd → μμ ) < 3.9x10-8 @90% CL


Below the eps versions of all figures available for download.


If you have access to internal CDFnotes, more details about the various acceptances and efficiencies can be found in these cdfnotes:

A full description of the analysis is in cdfnote 7463

The pre-blessing talk and blessing talk at the B Physics meeting also offers a summary of the analysis.

Experimental Papers and Status

Below are links the relevant experimental papers:

Theory Papers

Below are links to some relevant theory papers: Example Feynman diagrams: