Evidence for B+ -> omega l+ nu

Abstract

We have searched for the decay B^+ -> omega l^+ nu in 78 fb^-1 of Y(4S) data (85.0 million BBbar events) accumulated with the Belle detector. The final state is fully reconstructed using the omega decay into pi^+ pi^- pi^0 and the detector hermeticity to infer the neutrino momentum. The signal yield is extracted by a two-dimensional fit to the lepton momentum and the invariant p^i+ pi^- pi^0 mass. The result of the fit depends on the form factor model assumed for the decay. Taking the average over three different models, 421 +/- 132 events are found in the data corresponding to a preliminary branching fraction of (1.4 +/- 0.4(stat) +/- 0.2(syst) +/- 0.3(model)) * 10^-4.