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

  • Author(s): Acharya, S;
  • Adamová, D;
  • Adler, A;
  • Adolfsson, J;
  • Rinella, GA;
  • Agnello, M;
  • Agrawal, N;
  • Ahammed, Z;
  • Ahmad, S;
  • Ahn, SU;
  • Akbar, Z;
  • Akindinov, A;
  • Al-Turany, M;
  • Albuquerque, DSD;
  • Aleksandrov, D;
  • Alessandro, B;
  • Alfanda, HM;
  • Molina, RA;
  • Ali, B;
  • Ali, Y;
  • Alici, A;
  • Alizadehvandchali, N;
  • Alkin, A;
  • Alme, J;
  • Alt, T;
  • Altenkamper, L;
  • Altsybeev, I;
  • Anaam, MN;
  • Andrei, C;
  • Andreou, D;
  • Andronic, A;
  • Anguelov, V;
  • Antičić, T;
  • Antinori, F;
  • Antonioli, P;
  • Anuj, C;
  • Apadula, N;
  • Aphecetche, L;
  • Appelshäuser, H;
  • Arcelli, S;
  • Arnaldi, R;
  • Arratia, M;
  • Arsene, IC;
  • Arslandok, M;
  • Augustinus, A;
  • Averbeck, R;
  • Aziz, S;
  • Azmi, MD;
  • Badalà, A;
  • Baek, YW;
  • Bai, X;
  • Bailhache, R;
  • Bala, R;
  • Balbino, A;
  • Baldisseri, A;
  • Ball, M;
  • Banerjee, D;
  • Barbera, R;
  • Barioglio, L;
  • Barlou, M;
  • Barnaföldi, GG;
  • Barnby, LS;
  • Barret, V;
  • Bartels, C;
  • Barth, K;
  • Bartsch, E;
  • Baruffaldi, F;
  • Bastid, N;
  • Basu, S;
  • Batigne, G;
  • Batyunya, B;
  • Bauri, D;
  • Alba, JLB;
  • Bearden, IG;
  • Beattie, C;
  • Belikov, I;
  • Hechavarria, ADCB;
  • Bellini, F;
  • Bellwied, R;
  • Belokurova, S;
  • Belyaev, V;
  • Bencedi, G;
  • Beole, S;
  • Bercuci, A;
  • Berdnikov, Y;
  • Berdnikova, A;
  • Berenyi, D;
  • Bergmann, L;
  • Besoiu, MG;
  • Betev, L;
  • Bhaduri, PP;
  • Bhasin, A;
  • Bhat, IR;
  • Bhat, MA;
  • Bhattacharjee, B;
  • Bhattacharya, P;
  • Bianchi, A;
  • Bianchi, L;
  • Bianchi, N;
  • Bielčík, J
  • et al.
Abstract

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 rapidity 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 corresponding to an integrated luminosity of about 233 μb - 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 moderate 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 dependence 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.

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