First observation of the decay $B_{s2}^{\ast }(5840{)}^0\to B^{\ast +}{K}^{-}$ and studies of excited $B_s$ mesons

Abstract

Properties of the orbitally excited (L=1) $B_s$ states are studied using 1.0 fb${}^{-1}$ of pp collisions at $\sqrt{s}=7$ TeV collected with the LHCb detector. The first observation of the $B_{s2}^{\ast }(5840{)}^0$ meson decaying to $B^{\ast +}{K}^{-}$ is reported, and the corresponding branching fraction measured relative to the $B^{+}{K}^{-}$ decay mode. The $B_{s1}(5830{)}^0\to B^{\ast +}{K}^{-}$ decay is observed as well. The width of the $B_{s2}^{\ast }(5840{)}^0$ state is measured for the first time and the masses of the two states are determined with the highest precision to date. The observation of the $B_{s2}^{\ast }(5840{)}^0\to B^{\ast +}{K}^{-}$ decay favours the spin-parity assignment $J^P=2^{+}$ for the $B_{s2}^{\ast }(5840{)}^0$ meson. In addition, the most precise measurement of the mass difference $m(B^{\ast +})-m(B^{+})=45.01\pm 0.30(stat)\pm 0.23(syst)$ MeV/$c^2$ is obtained.

9 pages, 2 figures