Measurement of the B$^{\pm}$ production cross-section at LHCb

We present a preliminary measurement of the total and differential cross-section ${\rm d}\sigma/{\rm d} p_{\rm T}^{B}$ of $B^\pm$ mesons in proton-proton collisions at $\sqrt{s}$=7Tev using 35 pb$^{-1}$ of data collected by the LHCb detector in 2010. The $B^\pm$ meson is reconstructed in the exclusive decay $B^\pm\to J/\psi K^\pm$, with $J/\psi \to \mu^+ \mu^-$. The total cross-section in the rapidity range $y\in[2,4.5]$ is measured to be $\sigma(B^\pm, y \in[2,4.5]) = 37.1 \pm 1.9\,({\rm stat.}) \pm 5.3\,({\rm syst.}) \,{\rm \mu b}$.