Measurement of $B$ meson production cross-sections in proton-proton collisions at $\sqrt{s}=$ 7 TeV

The production cross-sections of $B$ mesons are measured using data, corresponding to a integrated luminosity of $0.36{\rm fb^{-1}}$, collected with the LHCb detector at a centre-of-mass energy of 7 TeV. The $B^+$, $B^0$ and $B_s^0$ mesons are reconstructed in the exclusive decays $B^+\to J/\psi K$, $B^0\to J/\psi K^{*0}$ and $B^0_s\to J/\psi\phi$, with $J/\psi\to\mu^+\mu^-$, $K^{*0}\to K^+\pi^-$ and $\phi\to K^+K^-$. The differential cross-sections as functions of $B$ meson transverse momentum $p_{\rm T}$ and rapidity $y$, in the range 0 < $p_{\rm T}<40\;{\rm GeV}/c^2$ and 2.0<$y$<4.5, are measured. The integrated cross-sections in the same $p_{\rm T}$ and $y$ range, including charge-conjugate states, are measured to be \begin{equation} \begin{array}{lcl} \sigma(pp\to B^++X) &=& 38.9\pm0.3\,({\rm stat.})\pm2.5\,({\rm syst.})\,\pm1.3({\rm norm.})\,{\rm \mu b}, \\ \sigma(pp\to B^0+X) &=& 38.1\pm0.6\,({\rm stat.})\pm3.7\,({\rm syst.})\,\pm4.7({\rm norm.})\,{\rm \mu b}, \\ \sigma(pp\to B^0_s+X) &=& 10.5\pm0.2\,({\rm stat.})\pm0.8\,({\rm syst.})\pm1.0\,({\rm norm.})\,{\rm \mu b}, \end{array} \nonumber \label{eq:result} \end{equation} where the third uncertainty arises from the pre-existing branching fraction measurements.