MMeasurement of ψ(2S) meson production in pp collisions at √s=7 TeV

CERN-LHC. The differential cross-section for the inclusive production of $\psi(2S)$ mesons in $pp$ collisions at $\sqrt{s}$=7 TeV has been measured with the LHCb detector. The data sample corresponds to an integrated luminosity of $36$ pb$^{-1}$. The $\psi(2S)$ mesons are reconstructed in the decay channels $\psi(2S) \rightarrow \mu^+ \mu^-$ and $\psi(2S) \rightarrow J/\psi \pi^+ \pi^-$, with the $J/\psi$ meson decaying into two muons. Results are presented both for promptly produced $\psi(2S)$ mesons and for those originating from $b$-hadron decays. In the kinematic range $p_{\rm T}(\psi(2S)) \le 16$ GeV/$c$ and $2 < y(\psi(2S)) \le 4.5$ we measure \begin{eqnarray*} \sigma_{\rm prompt}(\psi(2S)) &=&1.44 \pm 0.01~(\text{stat})\pm 0.12~(\text{syst})^{+0.20}_{-0.40}~(\text{pol})~{\rm \mu b}, \\ \sigma_{b}(\psi(2S)) &=&0.25 \pm 0.01~(\text{stat}) \pm 0.02~(\text{syst})~{\rm \mu b}, \end{eqnarray*} where the last uncertainty on the prompt cross-section is due to the unknown $\psi(2S)$ polarization. Recent QCD calculations are found to be in good agreement with our measurements. Combining the present result with the LHCb $J/\psi$ measurements we determine the inclusive branching fraction \begin{equation*} \mathcal{B}(b \rightarrow \psi(2S) X) = (2.73 \pm 0.06~(\text{stat}) \pm 0.16~(\text{syst}) \pm 0.24~(\text{BF})) \times 10^{-3}, \end{equation*} where the last uncertainty is due to the $\mathcal{B}(b \rightarrow J/\psi X)$, $\mathcal{B}(J/\psi \rightarrow \mu^+ \mu^-)$ and $\mathcal{B}(\psi(2S) \rightarrow e^+ e^-)$ branching fraction uncertainties.