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

Abstract

Measurements are reported of the central exclusive production of J/ψ and ψ(2S) 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 < η < 4.5, are measured to be σ J/ψ→µ + µ − = 435 ± 18 ± 11 ± 17 pb σ ψ(2S)→µ + µ − = 11.1 ± 1.1 ± 0.3 ± 0.4 pb. 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.

Recent ALICE results on coherent J/psi photoproduction in ultra-peripheral Pb-Pb collisions

“…The ratio was found to be in reasonable agreement both with the ratio of photoproduction cross sections off protons measured by the H1 Collaboration in ep collisions [12], by the LHCb Collaboration in pp collisions [13] and with LTA predictions for Pb-Pb UPC.…”

Quarkonia: Experimental summary

“…Measuring the quarkonium photoproduction cross section as a function of W the center-of-mass energy of the γp system allows one to compare results obtained at different energies and quarkonium rapidity ranges. For J/ψ, a common trend is observed for measurements carried out by LHCb in pp collisions at √ s = 7 and 13 TeV, ALICE, H1 and ZEUS as well as several other fixed-target experiments [32]. This trend is well reproduced by pQCD NLO calculations from the JMRT group [33].…”

Exclusive photoproduction of excited quarkonia in ultraperipheral collisions

“…More recently, the ultraperipheral pA and AA collisions (UPCs) at the LHC have provided clean experimental means for probing the real photoproduction mechanisms of heavy quarkonia in photon-Pomeron fusion with intact colliding nucleons or nuclei, thanks to low QCD backgrounds. Over the past few years, a wealth of phenomenological information on elastic (exclusive) and quasielastic J=ψ ≡ ψð1SÞ and ψ 0 ≡ ψð2SÞ photoproduction in UPCs has become available from the LHC measurements, in particular, from LHCb [12][13][14], ALICE [15][16][17][18][19], and CMS [20,21] experiments. Meanwhile, the existing theoretical approaches remain rather uncertain due to poorly known nonperturbative and a D-wave admixture in the corresponding S-wave quarkonia wave functions [22][23][24], as well as the coherence phenomena particularly relevant for photoproduction in AA UPCs [1,[25][26][27].…”