Coherent J/ψ and ψ' photoproduction at midrapidity in ultra-peripheral Pb–Pb collisions at √sNN = 5.02 TeV

• Autor(a) principal: Acharya, Shreyasi
• Data de Publicação: 2021
• Outros Autores: Gay Ducati, Maria Beatriz, Pereira, Luis Gustavo, Pezzi, Rafael Peretti, ALICE Collaboration
• Tipo de documento: Artigo
• Idioma: eng
• Título da fonte: Repositório Institucional da UFRGS
• Texto Completo: http://hdl.handle.net/10183/235109
• topic: Aceleradores de partículas; Colisao de ions pesados; Mésons psi

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