b --> s gamma using a Sum of Exclusive Modes

TL;DR

This paper reports preliminary measurements of the inclusive b --> s gamma decay using data from the BaBar detector, including branching fractions, gamma energy spectrum moments, and HQET parameter constraints.

Contribution

It introduces a method combining multiple exclusive channels to measure the inclusive b --> s gamma decay and constrains HQET parameters using the measured spectra.

Findings

Branching fraction B(b --> s gamma) = (4.3 +/- 0.5 +/- 0.8 +/- 1.3) x 10^-4

First moment of gamma energy spectrum measured, constraining LambdaBar

Constraints on HQET parameter lambda_1 obtained

Abstract

This paper describes preliminary results on the inclusive process b --> s gamma obtained from 20.7 fb^-1 of data recorded with the BaBar detector during 1999-2000. Signal event yields are found from a combination of twelve exclusive decay channels after subtracting continuum and BBbar backgrounds. Cross-feed from incorrectly reconstructed b --> s gamma events is also removed. Branching fractions in bins of hadronic mass are calculated using corrected Monte Carlo signal efficiencies; this is equivalent to measuring the gamma energy spectrum. We measure the first moment of the gamma energy spectrum constraining the HQET parameter LambdaBar = (0.37 +/- 0.09 (stat) +/- 0.07 (syst) +/- 0.10 (model)) GeV/c^2. A fit to the hadronic mass spectrum gives B(b --> s gamma) = (4.3 +/- 0.5 (stat) +/- 0.8 (syst) +/- 1.3 (model))x 10^-4 for the inclusive branching fraction. We also constrain the HQET parameter lambda_1.