Measurement of the $B_c^+$ to $B^+$ production cross-section ratios at $\sqrt{s}$ = 7 TeV in LHCb

The production of $B_c^+$ mesons in proton-proton collisions at a centre-of-mass energy of $\sqrt{s}$ = 7 TeV is studied with the LHCb detector. The analysis is based on a data sample of 32.5 pb$^{-1}$ collected between August and November 2010 at the Large Hadron Collider. The $B_c^+$ is reconstructed in the decay mode $B_c^+\to J/\psi \pi^+$. The ratio of $B_c^+$ to $B^+ \to J/\psi K^+$ decay yields is measured, in the fiducial region $p_T$ > 4 Gev/$c$ and 2.5 < $\eta$ < 4.5, equal to \begin{equation*} R_{c+}=\frac{\sigma\left(B_c^+\right) \times {\cal B}\left( B_c^+\to J/\psi \pi^+ \right)}{\sigma\left(B^+\right) \times {\cal B}\left( B^+\to J/\psi K^+ \right)} = (2.2\pm0.8\pm0.2)\% \end{equation*} where the first uncertainty is statistical and the second systematic.