Measurements of $B_c^{+}$ Production and Mass with the $B_c^{\mathbf{+}}\to J/\psi {\pi }^{\mathbf{+}}$ Decay

Measurements of $B_c^{+}$ production and mass are performed with the decay mode $B_c^{+}\to J/\psi {\pi }^{+}$ using $0.37{\mathrm{fb}}^{-1}$ of data collected in $pp$ collisions at $\sqrt{s}=7\mathrm{TeV}$ by the LHCb experiment. The ratio of the production cross section times branching fraction between the $B_c^{+}\to J/\psi {\pi }^{+}$ and the $B^{+}\to J/\psi K^{+}$ decays is measured to be $\mathbf{(}0.68\pm 0.10(\mathrm{stat})\pm 0.03(\mathrm{syst})\pm 0.05(\mathrm{\text{lifetime}})\mathbf{)}\%$ for $B_c^{+}$ and $B^{+}$ mesons with transverse momenta $p_{\mathrm{T}}>4\mathrm{GeV}/c$ and pseudorapidities $2.5<\eta <4.5$. The $B_c^{+}$ mass is directly measured to be $6273.7\pm 1.3(\mathrm{stat})\pm 1.6(\mathrm{syst})\mathrm{MeV}/c^2$, and the measured mass difference with respect to the $B^{+}$ meson is $M(B_c^{+})-M(B^{+})=994.6\pm 1.3(\mathrm{stat})\pm 0.6(\mathrm{syst})\mathrm{MeV}/c^2$.

Figure 1

Invariant mass distributions of selected (a) $B_c^{+}\to J/\psi {\pi }^{+}$ candidates and (b) $B^{+}\to J/\psi K^{+}$ candidates, used in the production measurement. The fits to the data are superimposed.

Figure 2

Invariant mass distribution of $B_c^{+}\to J/\psi {\pi }^{+}$ decays, used in the mass measurement. The fit to the data is superimposed.