Measurement of the Bs0→J/ψK*0 branching fraction and angular amplitudes

A sample of 114±11 Bs0→J/ψK -π + signal events obtained with 0.37fb -1 of pp collisions at √s=7TeV collected by the LHCb experiment is used to measure the branching fraction and polarization amplitudes of the Bs0→J/ψK *0 decay, with K *0→K -π +. The K -π + mass spectrum of the candidates in the Bs0 peak is dominated by the K *0 contribution. Subtracting the nonresonant K -π + component, the branching fraction of Bs0→J/ψK *0 is (4.4-0.4+0.5±0.8)×10 -5, where the first uncertainty is statistical and the second is systematic. A fit to the angular distribution of the decay products yields the K *0 polarization fractions f L=0.50±0.08±0.02 and f=0.19-0.08+0.10±0.02.