Measurement of the $\Upsilon$ (1$\cal S$) production cross-section at $\sqrt{s}$ = 7 TeV in LHCb

We study the production of $\Upsilon$ (1$\cal S$) mesons in proton-proton collisions at a centre-of-mass energy of $\sqrt{s}$ = 7 TeV with the LHCb detector. We measure the differential production cross-section as a function of the $\Upsilon$ (1$\cal S$) transverse momentum in the range $p_{\rm{T}}$ in [0;15] GeV$c$ and rapidity in the range y $\in$[2.0;4.5]. The analysis is based on a data sample of 32.4 pb$^-1$ collected between April and November 2010 at the Large Hadron Collider. The $\Upsilon$ (1$\cal S$) mesons are reconstructed in the decay mode $\Upsilon$ (1$\cal S$) $\to\mu^+\mu^-$ and the signal yields are extracted from a fit to the $\mu^+\mu^-$ invariant mass distribution. Integrating over the above kinematic ranges, we measure \begin{align} \sigma (pp \to \Upsilon (1\cal S); 0 < p_{\rm T} < 15 {\rm GeV}/c, 2 < y < 4.5) = 108.3\pm 0.7^{+30.9}_{-25.8}{\rm {nb}}, \end{align} where the first uncertainty is statistical and the second systematic. We compare our preliminary results with theoretical models and find reasonable agreement.