Measurement of the B -> Xs l+ l- branching fraction with a sum over exclusive modes

TL;DR

This paper reports a measurement of the inclusive branching fraction for the rare decay B -> Xs l+ l- using a large data sample, reconstructing multiple exclusive modes, and observing a significant signal consistent with Standard Model predictions.

Contribution

First measurement of the inclusive B -> Xs l+ l- branching fraction using a sum over exclusive modes with detailed systematic analysis.

Findings

Branching fraction B(B -> Xs l+ l-) = (5.6 +/- 1.5 (stat) +/- 0.6 (syst) +/- 1.1 (model)) x 10^-6

Observed 40 +/- 10 signal events with statistical significance

Method combines multiple exclusive decay modes to estimate inclusive rate.

Abstract

We measure the branching fraction for the flavor-changing neutral-current process B -> Xs l+ l- with a sample of 89 x 10^6 Upsilon(4S) -> BBbar events recorded with the BaBar detector at the PEP-II e+e- storage ring. The final state is reconstructed from e+e- or mu+mu- pairs and a hadronic system consisting of one K or K0s and up to two pions, with at most one pi0. We observe a signal of 40 +/- 10(stat) +/- 2(syst) events and extract the inclusive branching fraction B(B -> Xs l+ l-) = (5.6 +/- 1.5(stat) +/- 0.6(exp syst) +/- 1.1(model syst)) x 10^-6 for mll > 0.2 GeV/c^2.