UC Santa Cruz

The decays Bc+→J/ψDs+$$B_c^+ \rightarrow J/\psi D_s^+$$ and Bc+→J/ψDs∗+$$B_c^+ \rightarrow J/\psi D_s^{*+}$$ are studied with the ATLAS detector at the LHC using a dataset corresponding to integrated luminosities of 4.9 and 20.6 fb-1$$^{-1}$$ of pp collisions collected at centre-of-mass energies s=7$$\sqrt{s} = 7$$ TeV and 8 TeV, respectively. Signal candidates are identified through J/ψ→μ+μ-$$J/\psi \rightarrow \mu ^+\mu ^-$$ and Ds(∗)+→ϕπ+(γ/π0)$$D_s^{(*)+}\rightarrow \phi \pi ^+(\gamma /\pi ^0)$$ decays. With a two-dimensional likelihood fit involving the Bc+$$B_c^+$$ reconstructed invariant mass and an angle between the μ+$$\mu ^+$$ and Ds+$$D_s^+$$ candidate momenta in the muon pair rest frame, the yields of Bc+→J/ψDs+$$B_c^+ \rightarrow J/\psi D_s^+$$ and Bc+→J/ψDs∗+$$B_c^+ \rightarrow J/\psi D_s^{*+}$$, and the transverse polarisation fraction in Bc+→J/ψDs∗+$$B_c^+ \rightarrow J/\psi D_s^{*+}$$ decay are measured. The transverse polarisation fraction is determined to be Γ±±(Bc+→J/ψDs∗+)/Γ(Bc+→J/ψDs∗+)=0.38±0.23±0.07$$\Gamma _{\pm \pm }(B_c^+ \rightarrow J/\psi D_s^{*+})/\Gamma (B_c^+ \rightarrow J/\psi D_s^{*+}) = 0.38 \pm 0.23 \pm 0.07$$, and the derived ratio of the branching fractions of the two modes is BBc+→J/ψDs∗+/BBc+→J/ψDs+=2.8-0.8+1.2±0.3$$\mathcal {B}_{B_c^+ \rightarrow J/\psi D_s^{*+}}/\mathcal {B}_{B_c^+ \rightarrow J/\psi D_s^+} = 2.8 \,^{+1.2}_{-0.8} \pm 0.3$$, where the first error is statistical and the second is systematic. Finally, a sample of Bc+→J/ψπ+$$B_c^+\rightarrow J/\psi \pi ^+$$ decays is used to derive the ratios of branching fractions BBc+→J/ψDs+/BBc+→J/ψπ+=3.8±1.1±0.4±0.2$$\mathcal {B}_{B_c^+ \rightarrow J/\psi D_s^+}/\mathcal {B}_{B_c^+ \rightarrow J/\psi \pi ^+} = 3.8 \pm 1.1 \pm 0.4 \pm 0.2$$ and BBc+→J/ψDs∗+/BBc+→J/ψπ+=10.4±3.1±1.5±0.6$$\mathcal {B}_{B_c^+ \rightarrow J/\psi D_s^{*+}}/\mathcal {B}_{B_c^+ \rightarrow J/\psi \pi ^+} = 10.4 \pm 3.1 \pm 1.5 \pm 0.6$$, where the third error corresponds to the uncertainty of the branching fraction of Ds+→ϕ(K+K-)π+$$D_s^+\rightarrow \phi (K^+K^-)\pi ^+$$ decay. The available theoretical predictions are generally consistent with the measurement.