First observation of the decay B_c^+ to J/psi k+

Abstract

The decay B+ c → J/ψ K+ is observed for the first time using a data sample, corresponding to an integrated luminosity of 1.0 fb−1 , collected by the LHCb experiment in pp collisions at a centre-of-mass energy of 7 TeV. A yield of 46 ± 12 events is reported, with a significance of 5.0 standard deviations. The ratio of the branching fraction of B+ c → J/ψ K+ to that of B+ c → J/ψ π+ is measured to be 0.069 ± 0.019 ± 0.005, where the first uncertainty is statistical and the second is systematic.