Coherent $J/\psi$ and $\psi'$ photoproduction at midrapidity in ultra-peripheral Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}~=~5.02$ TeV

• Published in: The European physical journal. C, Particles and fields Vol. 81; no. 8
• Main Authors: Acharya, Shreyasi, Adamova, Dagmar, Adler, Alexander, Adolfsson, Jonatan, Aglieri Rinella, Gianluca, Agnello, Michelangelo, Agrawal, Neelima, Ahammed, Zubayer, Ahmad, Shakeel, Ahn, Sang Un, Akbar, Zaenal, Akindinov, Alexander, Al-Turany, Mohammad, Silva de Albuquerque, Danilo, Aleksandrov, Dmitry, Alessandro, Bruno, Alfanda, Haidar Mas'Ud, Alfaro Molina, Jose Ruben, Ali, Bushra, Ali, Yasir, Alici, Andrea, Alizadehvandchali, Negin, Alkin, Anton, Alme, Johan, Alt, Torsten, Altenkamper, Lucas, Altsybeev, Igor, Anaam, Mustafa, Andrei, Cristian, Andreou, Dimitra, Andronic, Anton, Anguelov, Venelin, Anticic, Tome, Antinori, Federico, Antonioli, Pietro, Chandra, Anuj, Apadula, Nicole, Aphecetche, Laurent Bernard, Appelshaeuser, Harald, Arcelli, Silvia, Arnaldi, Roberta, Arratia Munoz, Miguel Ignacio, Arsene, Ionut Cristian, Arslandok, Mesut, Augustinus, Andre, Averbeck, Ralf Peter, Aziz, Sizar, Azmi, Mohd Danish, Badala, Angela, Baek, Yongwook, Bai, Xiaozhi, Bailhache, Raphaelle Marie, Bala, Renu, Balbino, Alessandro, Baldisseri, Alberto, Ball, Markus, Banerjee, Debjani, Barbera, Roberto, Barioglio, Luca, Barlou, Maria, Barnafoldi, Gergely Gabor, Barnby, Lee Stuart, Ramillien Barret, Valerie, Bartels, Clara, Barth, Klaus, Bartsch, Esther, Baruffaldi, Filippo, Bastid, Nicole, Basu, Sumit, Batigne, Guillaume, Batyunya, Boris, Bauri, Dibakar, Bazo Alba, Jose Luis, Bearden, Ian Gardner, Beattie, Caitlin, Belikov, Iouri, Hechavarria, A.D.C. Bell, Bellini, Francesca, Bellwied, Rene, Belokurova, Svetlana, Belyaev, Vladimir, Bencedi, Gyula, Beole, Stefania, Bercuci, Alexandru, Berdnikov, Yaroslav, Berdnikova, Anastasia, Berenyi, Daniel, Bergmann, Luisa, Besoiu, Mihaela Gabriela, Betev, Latchezar, Bhaduri, Partha Pratim, Bhasin, Anju, Bhat, Inayat Rasool, Bhat, Mohammad Asif, Bhattacharjee, Buddhadeb, Bhattacharya, Purba, Bianchi, Antonio, Bianchi, Livio, Bianchi, Nicola, Bielcik, Jaroslav
• Format: Journal Article
• Language: English
• Published: Springer Verlag (Germany) 05.01.2021
• Subjects: High Energy Physics - Experiment; Nuclear Experiment; Physics; experimental results; gluon: shadowing; coherence; rapidity; psi: photoproduction; dilepton; parametrization; J/psi: photoproduction; 5020 GeV-cms/nucleon; heavy ion: scattering; rapidity dependence; ALICE; charmonium; suppression; anti-p p
• ISSN: 1434-6044; 1434-6052
• DOI: 10.1140/epjc/s10052-021-09437-6

The coherent photoproduction of $\rm{J/\psi}$ and $\rm{\psi'}$ mesons was measured in ultra-peripheral Pb-Pb collisions at a center-of-mass energy $\sqrt{s_{\mathrm{NN}}}~=~5.02$ TeV with the ALICE detector. Charmonia are detected in the central rapidity region for events where the hadronic interactions are strongly suppressed. The $\rm{J/\psi}$ is reconstructed using the dilepton ($l^{+} l^{-}$) and proton-antiproton decay channels, while for the $\rm{\psi'}$, 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 $\rm{J/\psi}$ and $\rm{\psi'}$ photoproduction. The coherent cross section is found to be in a good agreement with models incorporating moderate nuclear gluon shadowing of about 0.65 at a Bjorken-$x$ of around $6\times 10^{-4}$, such as the EPS09 parametrization, however none of the models is able to fully describe the rapidity dependence of the coherent $\rm{J/\psi}$ cross section including ALICE measurements at forward rapidity. The ratio of $\rm{\psi'}$ to $\rm{J/\psi}$ coherent photoproduction cross sections was also measured and found to be consistent with the one for photoproduction off protons.