Study of the Bc⁺ → J/ψ Ds⁺ and Bc⁺ → J/ψ Ds*⁺ decays with the ATLAS detector

Mullier, Geoffrey; Haug, Sigve; Weber, Michael; Meloni, Federico; Cervelli, Alberto; Beck, Hans Peter; Stucci, Stefania; Ereditato, Antonio (2016). Study of the Bc⁺ → J/ψ Ds⁺ and Bc⁺ → J/ψ Ds*⁺ decays with the ATLAS detector. European physical journal. C - particles and fields, 76(1) EDP Sciences 10.1140/epjc/s10052-015-3743-8

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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 fb⁻¹ 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 Ds(∗)⁺ → ϕπ⁺ (γ/π⁰) decays. With a two-dimensional likelihood fit involving the B + c reconstructed invariant mass and an angle between the μ⁺ and Ds⁺ candidate momenta in the muon pair rest frame, the yields of B⁺c →J/ψD + s and Bc⁺ → J/ψD∗s⁺, and the transverse polarisation fraction in Bc⁺ → J/ψD ∗+ s decay are measured. The transverse polarisation fraction is determined to be Γ ±± (B⁺c →J/ψD ∗s⁺)/Γ(Bc⁺ → 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 B B⁺c → J/ψDs⁺ /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.

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