Evidence for $b \to d \gamma$ Transitions From a Sum of Exclusive Final States in the Hadronic Final State Mass Range $1.0 {GeV}/c^2< M(X_d)<1.8 {GeV}/c^2$

Abstract

We present preliminary results of a search for $B\to X_d\gamma$ decays with a hadronic mass 1.0 GeV/$c^2<M(X_d)<$1.8 GeV/$c^2$. We consider seven final states with up to four charged pions and one neutral pion or $\eta$, which correspond to about 50% of the total $X_d$ fragmentation in this mass range. Based on a sample of 383 million $B\bar{B}$ events collected by the BaBar experiment at PEP-II, we measure a partial branching fraction $\sum\nolimits^{7}_{X_d=1}{{\ensuremath{\cal B}\xspace}}(B\to X_d\gamma)|_{(1.0{GeV}/c^2 <M(X_d)<1.8 {GeV}/c^2)}= (3.1\pm0.9 ^{+0.6}_{-0.5} \pm0.5)\cdot 10^{-6},$ where the uncertainties are statistical, systematic and model-dependent respectively.