Observation of the decay B¯s0→χc2K+ K− in the ϕ mass region

The (B) over bar (0)(s) -> chi(c2) K+ K- decay mode is observed and its branching fraction relative to the corresponding chi(c1) decay mode, in a +/- 15MeV/c(2) window around the phi mass, is found to be B ((B) over bar (0)(s) -> chi(c2) K+ K-)/B((B) over bar (0)(s) -> chi(c1) K+ K-) = (17.1 +/- 3.1 +/- 0.4 +/- 0.9)% where the fi rst uncertainty is statistical, the second systematic and the third due to the knowledge of the branching fractions of radiative chi(c) decays. The decay mode (B) over bar (0)(s) -> chi(c1) K+ K- allows the B-s(0) mass to be measured as m(B-s(0)) = 5366.83 +/- 0.25 +/- 0.27MeV/c(2), where the fi rst uncertainty is statistical and the second systematic. A combination of this result with other LHCb determinations of the B-s(0) mass is made.