The ALICE Collaboration at the LHC has mea- sured the J/ψ and ψ′ photoproduction at mid-rapidity in ultra-peripheral Pb–Pb collisions at √sNN = 2.76 TeV. The charmonium is identified via its leptonic decay for events where the hadronic activity is required to be mini- mal. The analysis is based on an event sample correspond- ing to an integrated luminosity of about 23 μb−1. The cross section for coherent and incoherent J/ψ production in the rapidity interval −0.9 < y < 0.9, are dσcoh/dy = J/ψ 2.38+0.34(sta+sys) mb and dσinc /dy = 0.98+0.19(sta + −0.24 J/ψ −0.17 sys) mb, respectively. The results are compared to theoret- ical models for J/ψ production and the coherent cross sec- tion is found to be in good agreement with those models in- corporating moderate nuclear gluon shadowing at Bjorken- x around 10−3, such as EPS09 parametrization. In addition the cross section for the process γ γ → e+e− has been mea- sured and found to be in agreement with models implement- ing QED at leading order.
Charmonium and e + e − pair photoproduction at mid-rapidity in ultra-peripheral Pb–Pb collisions at $\sqrt{s_{\mathrm{NN}}} = 2.76\ \mbox{TeV}$
ARNALDI, Roberta;BALA, RENU;BEOLE', Stefania;BERZANO, DARIO CARLO DOMENICO;BIANCHI, LIVIO;BOTTA, Elena;BRUNA, ELENA;BUFALINO, STEFANIA;CORRALES MORALES, YASSER;FERRETTI, Alessandro;GAGLIARDI, Martino;GALLIO, Mauro;INNOCENTI, GIAN MICHELE;LEONCINO, MARCO;MASERA, Massimo;MILANO, LEONARDO;OPPEDISANO, Chiara;RAMELLO, Luciano;RIVETTI, Angelo;RUSSO, RICCARDO;SCOMPARIN, ENRICO;SITTA, Mario;VALLERO, Sara;VERCELLIN, Ermanno;
2013-01-01
Abstract
The ALICE Collaboration at the LHC has mea- sured the J/ψ and ψ′ photoproduction at mid-rapidity in ultra-peripheral Pb–Pb collisions at √sNN = 2.76 TeV. The charmonium is identified via its leptonic decay for events where the hadronic activity is required to be mini- mal. The analysis is based on an event sample correspond- ing to an integrated luminosity of about 23 μb−1. The cross section for coherent and incoherent J/ψ production in the rapidity interval −0.9 < y < 0.9, are dσcoh/dy = J/ψ 2.38+0.34(sta+sys) mb and dσinc /dy = 0.98+0.19(sta + −0.24 J/ψ −0.17 sys) mb, respectively. The results are compared to theoret- ical models for J/ψ production and the coherent cross sec- tion is found to be in good agreement with those models in- corporating moderate nuclear gluon shadowing at Bjorken- x around 10−3, such as EPS09 parametrization. In addition the cross section for the process γ γ → e+e− has been mea- sured and found to be in agreement with models implement- ing QED at leading order.File | Dimensione | Formato | |
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