Studying a b-quark decaying to an s quark and a photon at BaBar using a fully inclusive method

The b → sγ decay represents a possible electromagnetic “loop” penguin decay of the B meson. This FCNC process is of high theoretical interest because various scenarios of new physics are expected to have contributions at the same (one loop) level as the Standard Model. The large sample of BB¯ meson decays collected by the BaBar experiment makes a precision measurement of this rare decay possible. In conjunction with Standard Model predictions at the 10% level, it brings new physics effects into the realm of detection—or seriously constrains models that could predict them.; A fully inclusive technique is presented to study the b → sγ transition as a function of photon energy, using 88.5 ± 1.0 × 106 BB¯ meson decays collected by the BaBar experiment in the years 2000 to 2002. The expected statistical and systematic uncertainties have been fully determined which enables first comparisons with theoretical predictions and other experimental results. It also lays the basis for the determination of the inclusive branching fraction $B$(B → X_sγ) and the measurement of the photon energy spectrum.