Study of the B⁺_c → J/ψ D⁺_s and B⁺_c→ J/ψ D^*+_s decays with the ATLAS detector

Abstract

The decays B⁺_c→J/ψD⁺_s and B⁺_c→J/ψD^*+_s are studied with the ATLAS detector at the LHC using a dataset corresponding to integrated luminosities of 4.9 and 20.6 fb⁻¹ of pp collisions collected at centre-of-mass energies √s=7 TeV and 8 TeV, respectively. Signal candidates are identified through J/ψ→μ+μ− and D^(*)+_s→ϕπ+(γ/π⁰) decays. With a two-dimensional likelihood fit involving the B⁺_c reconstructed invariant mass and an angle between the μ+ and D⁺_s candidate momenta in the muon pair rest frame, the yields of B⁺_c→J/ψD⁺_s and B⁺_c→J/ψD^*+_s, and the transverse polarisation fraction in B⁺_c→J/ψD^*+_s decay are measured. The transverse polarisation fraction is determined to be Γ±±(B⁺_c→J/ψD^*+_s)/Γ(B⁺_c→J/ψD^*+_s)=0.38±0.23±0.07, and the derived ratio of the branching fractions of the two modes is B_{B⁺_c→J/ψD^*+_s}/B_{B⁺_c→J/ψD⁺_s}=2.8+1.2−0.8±0.3 , where the first error is statistical and the second is systematic. Finally, a sample of B⁺_c→J/ψπ+ decays is used to derive the ratios of branching fractions BB_{B⁺_c→J/ψD^*+_s}/B_{B⁺_c→J/ψπ+}=3.8±1.1±0.4±0.2 and B_{B⁺_c→J/ψD^*+_s}/B_{B⁺_c→J/ψπ+}=10.4±3.1±1.5±0.6, where the third error corresponds to the uncertainty of the branching fraction of D⁺_s→ϕ(K+K−)π+ decay. The available theoretical predictions are generally consistent with the measurement.