First Observation of CP Violation and Measurement of Polarization in B+ →ρ (770)0K^∗(892)+ Decays

An amplitude analysis of the B+→(π+π-)(KS0π+) decay is performed in the mass regions 0.30<mπ+π-<1.10 GeV/c2 and 0.75<mKS0π+<1.20 GeV/c2, using pp collision data recorded with the LHCb detector corresponding to an integrated luminosity of 9 fb-1. The polarization fractions and CP asymmetries for B+→ρ(770)0K∗(892)+ decays are measured. Violation of the CP symmetry in the decay B+→ρ(770)0K∗(892)+ is observed for the first time, with a significance exceeding 9 standard deviations. The CP asymmetry is measured to be ACP=0.507±0.062(stat)±0.024(syst) and the CP-averaged longitudinal polarization fraction of fL=0.720±0.028(stat)±0.009(syst). The measurements help to shed light on the polarization puzzle of B mesons decaying to two vector mesons.