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The decays B+c→J/ψD+sBc+→J/ψDs+ and B+c→J/ψD∗+sBc+→J/ψDs∗+ are studied with the ATLAS detector at the LHC using a dataset corresponding to integrated luminosities of 4.9 and 20.6 fb−1−1 of ppcollisions collected at centre-of-mass energies s√=7s=7 TeV and 8 TeV, respectively. Signal candidates are identified through J/ψ→μ+μ−J/ψ→μ+μ− and D(∗)+s→ϕπ+(γ/π0)Ds(∗)+→ϕπ+(γ/π0) decays. With a two-dimensional likelihood fit involving the B+cBc+ reconstructed invariant mass and an angle between the μ+μ+ and D+sDs+ candidate momenta in the muon pair rest frame, the yields of B+c→J/ψD+sBc+→J/ψDs+and B+c→J/ψD∗+sBc+→J/ψDs∗+, and the transverse polarisation fraction in B+c→J/ψD∗+sBc+→J/ψDs∗+ 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±0.07Γ±±(Bc+→J/ψDs∗+)/Γ(Bc+→J/ψDs∗+)=0.38±0.23±0.07, and the derived ratio of the branching fractions of the two modes is BB+c→J/ψD∗+s/BB+c→J/ψD+s=2.8+1.2−0.8±0.3BBc+→J/ψDs∗+/BBc+→J/ψDs+=2.8−0.8+1.2±0.3, where the first error is statistical and the second is systematic. Finally, a sample of B+c→J/ψπ+Bc+→J/ψπ+ decays is used to derive the ratios of branching fractions BB+c→J/ψD+s/BB+c→J/ψπ+=3.8±1.1±0.4±0.2BBc+→J/ψDs+/BBc+→J/ψπ+=3.8±1.1±0.4±0.2 and BB+c→J/ψD∗+s/BB+c→J/ψπ+=10.4±3.1±1.5±0.6BBc+→J/ψDs∗+/BBc+→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+Ds+→ϕ(K+K−)π+ decay. The available theoretical predictions are generally consistent with the measurement.
Bibliographical noteComments: 17 pages plus author list + cover pages (33 pages total), 7 figures, 5 tables, submitted to Eur. Phys. J. C. All figures including auxiliary figures are available at https://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/BPHY-2014-04/
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