Observation of the Decay B[+ over c] →B[0 over s]π[superscript +]

Abstract

The result of a search for the decay B[+ over c] → B[0 over s]π[superscript +] is presented, using the B[0 over s] → D[bar over s]π[superscript +] and B[0 over s] → J/ψϕ channels. The analysis is based on a data sample of pp collisions collected with the LHCb detector, corresponding to an integrated luminosity of 1 fb[superscript −1] taken at a center-of-mass energy of 7 TeV, and 2 fb[superscript −1] taken at 8 TeV. The decay B[+ over c] → B[0 over s]π[superscript +] 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[+ over c])/σ(B[0 over s])] × B(B[+ over c] → B[0 over s]π[superscript +]) = [2.37 ± 0.31 (stat) ± 0.11 (syst)[+0.17 over −0.13](τ[subscript B][+ over c])] × 10[superscript −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[+ over c] lifetime. This is the first observation of a B meson decaying to another B meson via the weak interaction.