Coherent J/ψ photoproduction at forward rapidity in ultra-peripheral Pb–Pb collisions at sNN=5.02 TeV

J/ψ production as a function of charged-particle multiplicity in p-Pb collisions at $$ \sqrt{s_{\mathrm{NN}}} $$ = 8.16 TeV

“…They are compatible within uncertainties with the p-Pb backward rapidity result in the restricted multiplicity interval of the measurement. Whereas the pp and p-Pb data include J/ψ with p T > 0, the Pb-Pb data points include J/ψ with 0.3 < p T < 12 GeV/c to reduce the low-p T contribution from photoproduction, which is significant only in more peripheral collisions [62,64,65]. The overall increase of multiple parton-parton collisions with the colliding system (from pp up to Pb-Pb collisions) described in [66] is expected to cancel in the relative quantities reported in this publication, sensitive to the relative evolution with charged-particle density in a given colliding system.…”

“…The pp results are normalized to INEL collisions [29], whereas p-Pb ones refer to the NSD event class; all for p T > 0. The Pb-Pb data points include J/ψ with 0.3 < p T < 12 GeV/c to reduce the low-p T contribution from photoproduction, which is significant only in more peripheral collisions [62,64,65]. The vertical bars represent the statistical uncertainties, the boxes the systematic ones.…”

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].…”

Some recent results related to low-xand forwardphysics

“…The same process has been measured at the LHC in Pb-Pb UPC at √ s NN = 5.02 TeV, but in this case at forward rapidity. Preliminary results have been reported by LHCb [16], while ALICE recently published their measurement [9]. The rapidity dependence of the cross section for the coherent production of J/ψ vector mesons is shown in Fig.…”