Observation of the Bs0→J/ψ Ks0 K± π∓ decay

Decays of the form B(s)0 → J/ψ KS0h+h(′)- (h(′) = K, π) are searched for in proton-proton collision data corresponding to an integrated luminosity of 1.0 fb-1 recorded with the LHCb detector. The first observation of the B(s)0 → J/ψ KS0K±π∓ decay is reported, with significance in excess of 10 standard deviations. The B0→J/ψKs0K+K- decay is also observed for the first time. The branching fraction of B0→J/ψKs0π+π- is determined, to significantly better precision than previous measurements, using B0→ J/ψKs0 as a normal-isation channel. Branching fractions and upper limits of the other B(s)0→ J/ψKs0h+h(′)- modes are determined relative to that of the B0→ /ψKs0π+π- decay.