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

An amplitude analysis of the 𝐵+→(𝜋+⁢𝜋−)⁢(𝐾0S⁢𝜋+) decay is performed in the mass regions 0.30<𝑚𝜋+⁢𝜋−<1.10  GeV/𝑐2 and 0.75<𝑚𝐾0S⁢𝜋+<1.20  GeV/𝑐2, using 𝑝⁢𝑝 collision data recorded with the LHCb detector corresponding to an integrated luminosity of 9  fb−1. The polarization fractions and 𝐶⁢𝑃asymmetries for 𝐵+→𝜌⁢(770)0⁢𝐾*⁢(892)+ decays are measured. Violation of the 𝐶⁢𝑃 symmetry in the decay 𝐵+ →𝜌⁢(770)0⁢𝐾*⁢(892)+ is observed for the first time, with a significance exceeding 9 standard deviations. The 𝐶⁢𝑃 asymmetry is measured to be 𝒜𝐶⁢𝑃=0.507±0.062⁢(stat)±0.024⁢(syst) and the 𝐶⁢𝑃-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.