Measurement of the $B_s^0\to J/\ddot{I}ˆK^{\ast 0}$ branching fraction and angular amplitudes

Abstract

A search for the decay $B_s^0\to J/\ddot{I}ˆK^{\ast 0}$ with $K^{\ast 0}\to K^{-}\ddot{I}{€}^{+}$ is performed with 0.37 fb${}^{-1}$ of $pp$ collisions at $\sqrt{s}$ = 7 TeV collected by the LHCb experiment, finding a $\Bs \to JψK^-π^+$ peak of $114\pm 11$ signal events. The $K^{-}\ddot{I}{€}^{+}$ mass spectrum of the candidates in the $B_s^0$ peak is dominated by the $K^{\ast 0}$ contribution. Subtracting the non-resonant $K^{-}\ddot{I}{€}^{+}$ component, the branching fraction of \BsJpsiKst is $(4.4_{-0.4}^{+0.5}\pm 0.8)\times 10^{-5}$, where the first uncertainty is statistical and the second systematic. A fit to the angular distribution of the decay products yields the \Kst polarization fractions $f_L=0.50\pm 0.08\pm 0.02$ and $f_{||}=0.19_{-0.08}^{+0.10}\pm 0.02$.