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

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 $2.0<\hat{I}\cdot <4.5$, are measured to be $$\begin{array}{rcl}\ddot{I}{ƒ}_{J/\ddot{I}ˆ\to \hat{I}{¼}^{+}\hat{I}{¼}^{-}}& =& 435\pm 18\pm 17\pm 16\mathrm{pb},\\ \ddot{I}{ƒ}_{\ddot{I}ˆ(2S)\to \hat{I}{¼}^{+}\hat{I}{¼}^{-}}& =& 11.1\pm 1.1\pm 0.3\pm 0.4\mathrm{pb}.\end{array}$$ 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.

All figures and tables, and additional information, are available at https://lhcbproject.web.cern.ch/lhcbproject/Publications/p/LHCb-PAPER-2018-011.html