Observation of the Decay B+c→B0sπ+

Abstract

The result of a search for the decay B + c → B 0 s π + is presented, using the B 0 s → D − s π + and B 0 s → J / ψ ϕ channels. The analysis is based on a data sample of p p collisions collected with the LHCb detector, corresponding to an integrated luminosity of 1 fb − 1 taken at a center-of-mass energy of 7 TeV, and 2 fb − 1 taken at 8 TeV. The decay B + c → B 0 s π + is observed with significance in excess of 5 standard deviations independently in both decay channels. The measured product of the ratio of cross sections and branching fraction is [ σ ( B + c ) / σ ( B 0 s ) ] × B ( B + c → B 0 s π + ) = [ 2.37 ± 0.31 ( stat ) ± 0.11 ( syst ) + 0.17 − 0.13 ( τ B + c ) ] × 10 − 3 , in the pseudorapidity range 2 < η ( B ) < 5 , where the first uncertainty is statistical, the second is systematic, and the third is due to the uncertainty on the B + c lifetime. This is the first observation of a B meson decaying to another B meson via the weak interaction.