The coherent photoproduction of J/psi and psi' mesons was measured in ultra-peripheral Pb-Pb collisions at a center-of-mass energy root s(NN) = 5.02 TeV with the ALICE detector. Charmonia are detected in the central rapidity region for events where the hadronic interactions are strongly suppressed. The J/psi is reconstructed using the dilepton (l(+)l(-)) and proton-antiproton decay channels, while for the psi' the dilepton and the l(+)l(-) pi(+)pi(-) decay channels are studied. The analysis is based on an event sample corresponding to an integrated luminosity of about 233 mu b(-1). The results are compared with theoretical models for coherent J/psi and psi' photoproduction. The coherent cross section is found to be in a good agreement with models incorporating moderate nuclear gluon shadowing of about 0.64 at a Bjorken-x of around 6 x 10(-4), such as the EPS09 parametrization, however none of the models is able to fully describe the rapidity dependence of the coherent J/psi cross section including ALICE measurements at forward rapidity. The ratio of psi' to J/psi coherent photoproduction cross sections was also measured and found to be consistent with the one for photoproduction off protons.

Coherent J/psi and psi' photoproduction at midrapidity in ultra-peripheral Pb-Pb collisions at √s(NN)=5.02 TeV

Buckland, MD;Camerini, P;Contin, G;De Martin, C;Fragiacomo, E;Luparello, G;Margagliotti, GV;Piano, S;Rui, R;Zaccolo, V;
2021

Abstract

The coherent photoproduction of J/psi and psi' mesons was measured in ultra-peripheral Pb-Pb collisions at a center-of-mass energy root s(NN) = 5.02 TeV with the ALICE detector. Charmonia are detected in the central rapidity region for events where the hadronic interactions are strongly suppressed. The J/psi is reconstructed using the dilepton (l(+)l(-)) and proton-antiproton decay channels, while for the psi' the dilepton and the l(+)l(-) pi(+)pi(-) decay channels are studied. The analysis is based on an event sample corresponding to an integrated luminosity of about 233 mu b(-1). The results are compared with theoretical models for coherent J/psi and psi' photoproduction. The coherent cross section is found to be in a good agreement with models incorporating moderate nuclear gluon shadowing of about 0.64 at a Bjorken-x of around 6 x 10(-4), such as the EPS09 parametrization, however none of the models is able to fully describe the rapidity dependence of the coherent J/psi cross section including ALICE measurements at forward rapidity. The ratio of psi' to J/psi coherent photoproduction cross sections was also measured and found to be consistent with the one for photoproduction off protons.
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Utilizza questo identificativo per citare o creare un link a questo documento: http://hdl.handle.net/11368/3027847
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