Observation of the decay B¯0s→χc2K+K−B¯s0→χc2K+K− in the ϕ mass region

Abstract

The B¯¯¯¯0s→χc2K+K−B¯s0→χc2K+K− decay mode is observed and its branching fraction relative to the corresponding χc1 decay mode, in a ±15 MeV/c2 window around the ϕ mass, is found to beB(B¯¯¯¯0s→χc2K+K−)B(B¯¯¯¯0s→χc1K+K−)=(17.1±3.1±0.4±0.9)%,B(B¯s0→χc2K+K−)B(B¯s0→χc1K+K−)=(17.1±3.1±0.4±0.9)%,where the first uncertainty is statistical, the second systematic and the third due to the knowledge of the branching fractions of radiative χc decays. The decay mode B¯¯¯¯0s→χc1K+K−B¯s0→χc1K+K−allows the B s 0 mass to be measured asm(B0s)=5366.83±0.25±0.27 MeV/c2,m(Bs0)=5366.83±0.25±0.27 MeV/c2,where the first uncertainty is statistical and the second systematic. A combination of this result with other LHCb determinations of the B s 0 mass is made.