A Precision Measurement of the B ? X_sγ Branching Fraction

Radiative decays of B-mesons are ideal laboratories for probing New Physics (NP). Since flavor-changing neutral currents are forbidden at tree-level in the Standard Model (SM), a loop diagram is necessary to facilitate the B ? X_sγ transition, where X_s represents any strange hadronic final state. New Physics particles can potentially propagate in this loop, and if the NP couplings are comparableto those of the SM, deviations from the SM prediction of the B ? X_sγ branching fraction could be observed. The current SM prediction for BF(B ? X_sγ) has been obtained with good precision, requiring a precise measurement to make any definitive statement on the presence of NP.A precision measurement of the B ? X_sγ analysis at BABAR has been performed. To compare directly with the SM prediction, the B ? X_sγ branching fraction must be measured inclusively, where all X_s final states are taken into account. This is achieved by only reconstructing the high-energy photon from thedecay. Consequently, the signal is overwhelmed with backgrounds from continuum processes and non-signal B-meson decays. A series of selection criteria is imposed to suppress continuum background. The remaining continuum background is subtracted with data taken 40 MeV below the ̏'(4S) resonance. Photon backgrounds from BB events primarily originate from ̏‰âÂ⁰(Ì_åá) ? γ&gamma decays, as well as radiativedecays of ̏'¡ and Ì_åá' mesons. Energy deposits from electrons and antineutrons alsoimitate photons from B ? X_sγ decays. These backgrounds are subtracted using data-corrected Monte Carlo (MC) simulation of BB events.The signal region of 1.8 < E_γ* < 2.8 GeV is not looked at until the selection criteria and data-corrected MC backgrounds are fixed. A set of control region checks must be satisfied before the signal region is unblinded, after which the background-subtracted photon spectrum is efficiency-corrected. After a series of corrections related to reference frame differences, photon energy extrapolation, and removal of the B ? X_dγ contribution, a total branching fraction is obtained:BF(B ? X_sγ)_{Eγ* >1.6GeV} = (3.28 Ìâå± 0.16 Ìâå± 0.28 Ìâå± 0.10) ÌÄ' 10^Ì¢è '4 , where the errors are the statistical, systematic, and model-dependent uncertainties, respectively. This result is consistent with the SM and can be used to place stringent constraints on NP theories.