Search for the decay Bs0→D^*aπ±

A search for the decay Bs0→D ^{* â̂}π ^± is presented using a data sample corresponding to an integrated luminosity of 1.0 fb ^-1 of pp collisions collected by LHCb. This decay is expected to be mediated by a W-exchange diagram, with little contribution from rescattering processes, and therefore a measurement of the branching fraction will help us to understand the mechanism behind related decays such as Bs0→π ⁺π ^- and Bs0→DD̄. Systematic uncertainties are minimized by using B0→D ^*â̂π ^± as a normalization channel. We find no evidence for a signal, and set an upper limit on the branching fraction of B(Bs0→D ^{* â̂}π ^±)<6.1(7.8)×10 ^-6 at 90% (95%) confidence level.