Measurement of the Bs0 → J/ψ (K)over-bar*0 branching fraction and angular amplitudes

A sample of 114 +/- 11 B-s(0) -> J/psi K- pi(+) signal events obtained with 0.37 fb(-1) of pp collisions at root s = 7 TeV collected by the LHCb experiment is used to measure the branching fraction and polarization amplitudes of the B-s(0) -> J/psi(K) over bar*(0) decay, with (K) over bar*(0) -> K- pi(+). The K- pi(+) mass spectrum of the candidates in the B-s(0) peak is dominated by the (K) over bar*(0) contribution. Subtracting the nonresonant K- pi(+) component, the branching fraction of B-s(0) -> J/pi (K) over bar*(0) is (4.4(-0.4)(+0.5) +/- 0.8) x 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(parallel to) = 0.19(-0.08)(+0.10) +/- 0.02.