A Combination of CDF and DO Limits on the Branching Ratio of B_s(d) to mu+ mu- Decays

We combine the results of CDF and DØ searches for the rare decays B 0 s → µ + µ − and B 0 d → µ + µ − . The experiments use 364 pb − 1 and 300 pb − 1 of data respectively. The limits on the branching ratios are obtained by normalizing the estimated sensitivity to the decay B + → J/ψK + taking into account the fragmentation ratios f u /f s ( d ) . The combined results exclude branching ratios of BR( B 0 s → µ + µ − ) > 1 . 5 × 10 − 7 and BR( B 0 d → µ + µ − ) > 4 . 0 × 10 − 8 at 95% confidence level. These are the most stringent limits on these decays at the present time.