Exclusive $J/\psi$ and $\psi(2S)$ production in $pp$ collisions at $\sqrt{s}=7$ TeV

TL;DR

This paper reports measurements of exclusive $J/$ and $(2S)$ meson production in proton-proton collisions at 7 TeV, providing data that align with previous experiments and theoretical models, and exploring photoproduction cross-sections.

Contribution

First measurement of exclusive $J/$ and $(2S)$ production cross-sections at 7 TeV in the LHCb detector, including photoproduction cross-section as a function of energy.

Findings

Measured cross-sections agree with previous results and predictions.

Photoproduction cross-section follows a power law similar to HERA data.

Results support existing theoretical models of vector meson production.

Abstract

Exclusive $J/\psi$ and $\psi(2S)$ vector meson production has been observed in the dimuon channel using the LHCb detector. The cross-section times branching fractions to two muons with pseudorapidities between 2.0 and 4.5 are measured to be $ \sigma_{pp\rightarrow J/\psi (\rightarrow \mu^{+} \mu^{-})} (2.0 <\eta_{\mu^{\pm}}< 4.5) = 307 \pm 21 \pm 36 \text{pb}, \sigma_{pp\rightarrow \psi(2S) (\rightarrow \mu^{+} \mu^{-})} (2.0 <\eta_{\mu^{\pm}}< 4.5) = 7.8 \pm 1.3 \pm 1.0 \text{pb}, $ where the first uncertainties are statistical and the second are systematic. The measurements are found to be in good agreement with results from previous experiments and theoretical predictions. The $J/\psi$ photoproduction cross-section has been measured as a function of the photon-proton centre-of-mass energy. The results are consistent with measurements obtained at HERA and confirm a similar power law behaviour for the photoproduction cross-section.