Search for $B_s \rightarrow \mu^{+}\mu^{-}$ and $B_d \rightarrow \mu^{+}\mu^{-}$ decays with the full CDF Run II data set

TL;DR

This paper reports a search for rare B meson decays into muon pairs using the full CDF Run II dataset, finding an excess consistent with the Standard Model prediction and setting upper limits on the branching fractions.

Contribution

The study provides the first full dataset analysis of B_s and B_d decays into muon pairs at the Tevatron, including the observation of an excess for B_s decays and new upper limits.

Findings

Observed an excess of B_s → μ+μ− candidates with a 6.8% probability of being background fluctuation.

Set an upper limit on B_d → μ+μ− branching fraction at 4.6×10^−9.

Measured B_s → μ+μ− branching fraction as (1.3^{+0.9}_{−0.7})×10^−8.

Abstract

We report on a search for \bsmm\ and \bdmm\ decays using proton-antiproton collision data at $\sqrt{s}=1.96$ TeV corresponding to $10 \fb$ of integrated luminosity collected by the CDF detector at the Fermilab Tevatron collider. The observed number of \bd\ candidates is consistent with background-only expectations and yields an upper limit on the branching fraction of $\brbdmm < 4.6\times 10^{-9}$ at 95% confidence level. We observe an excess of \bs\ candidates. The probability that the background processes alone could produce such an excess or larger is 0.94%. The probability that the combination of background and the expected standard model rate of \bsmm\ could produce such an excess or larger is 6.8%. These data are used to determine a branching fraction $\brbsmm = (1.3^{+0.9}_{-0.7}) \times 10^{-8} $ and provide an upper limit of $\brbsmm < 3.1\times 10^{-8}$ at 95% confidence level.