Search for B_s --> mu+mu- and B_d --> mu+mu- Decays with CDF II

Understand

A search has been performed for B_s --> mu+mu- and B_d --> mu+mu- decays using 7/fb of integrated luminosity collected by the CDF II detector at the Fermilab Tevatron collider.

• The observed number of B_d candidates is consistent with background-only expectations and yields an upper limit on the branching fraction of BF(B_d-->mu+mu-) < 6.0E-9 at 95% confidence level.
• We observe an excess of B_s candidates.
• The probability that the background processes alone could produce such an excess or larger is 0.27%.