First observation of the rareB+→D+K+π−decay

The Bþ → DþKþπ− decay is observed in a data sample corresponding to 3.0 fb−1 of pp collision data recorded by the LHCb experiment during 2011 and 2012. The signal significance is 8σ and the branching fraction is measured to be BðBþ → DþKþπ−Þ¼ð5.31 0.90 0.48 0.35Þ × 10−6, where the uncertainties are statistical, systematic and due to the normalization mode Bþ → D−Kþπþ, respectively. The Dalitz plot appears to be dominated by broad structures. Angular distributions are exploited to search for quasi-two-body contributions from Bþ → D 2ð2460Þ0Kþ and Bþ → DþKð892Þ0 decays. No significant signals are observed and upper limits are set on their branching fractions.