Central exclusive production of $J/\psi$ and $\psi(2S)$ mesons in $pp$ collisions at $\sqrt{s}=13~$TeV

TL;DR

This paper reports measurements of central exclusive production of J/psi and psi(2S) mesons in proton-proton collisions at 13 TeV, with reduced backgrounds and detailed cross-section results that agree with theoretical predictions.

Contribution

First measurements at 13 TeV with improved background suppression and detailed cross-section analysis for J/psi and psi(2S) mesons in central exclusive production.

Findings

Measured cross-sections for J/psi and psi(2S) decays to dimuons.

Good agreement with theoretical predictions.

Observed deviation from simple power-law extrapolation at lower energies.

Abstract

Measurements are reported of the central exclusive production of \jpsi and \psitwos mesons in $pp$ collisions at a centre-of-mass energy of 13 TeV. Backgrounds are significantly reduced compared to previous measurements made at lower energies through the use of new forward shower counters. The products of the cross-sections and the branching fractions for the decays to dimuons, where both muons are within the pseudorapidity range $2.0<\eta<4.5$, are measured to be $$ \begin{array}{rcl} \sigma_{J/\psi\rightarrow\mu^+\mu^-}&=&435 \pm 18 \pm 17 \pm 16 {\rm \ pb},\\ \sigma_{\psi(2S)\rightarrow\mu^+\mu^-}&=&11.1 \pm 1.1 \pm 0.3 \pm 0.4 {\rm \ pb}.\\ \end{array} $$ The first uncertainties are statistical, the second are systematic, and the third are due to the luminosity determination. The cross-sections are also measured differentially for meson rapidities between 2.0 and 4.5. Good agreement is observed with theoretical predictions. Photoproduction cross-sections are derived and compared to previous experiments, and a deviation from a pure power-law extrapolation of lower energy data is observed.