First measurement of the |t|-dependence of coherent J/ψ photonuclear production
S. Acharya, D. Adamová, A. Adler, Jonatan Adolfsson, G. Aglieri Rinella, M. Agnello, N. Agrawal, Z. Ahammed, S. Ahmad, S. U. Ahn, Zaenal Akbar, A. Akindinov, M. Al-Turany, D. S. D. Albuquerque, D. Aleksandrov, B. Alessandro, H. M. Alfanda, R. Alfaro Molina, Bushra Ali, Y. Ali, A. Alici, N. Alizadehvandchali, A. Alkin, J. Alme, T. Alt, L. Altenkamper, I. Altsybeev, M. N. Anaam, C. Andrei, D. Andreou, A. Andronic, V. Anguelov, T. Antičić, F. Antinori, P. Antonioli, C. Anuj, N. Apadula, L. Aphecetche, H. Appelshäuser, S. Arcelli, R. Arnaldi, M. Arratia, I.C. Arsene, M. Arslandok, A. Augustinus, R. Averbeck, S. Aziz, M. D. Azmi, A. Badalà, Y. W. Baek, Xiaoshuan Bai, R. Bailhache, R. Bala, A. Balbino, A. Baldisseri, M. Ball, D. Banerjee, R. Barbera, L. Barioglio, M. Barlou, G. G. Barnaföldi, L. S. Barnby, V. Barret, C. Bartels, K. Barth, E. Bartsch, F. Baruffaldi, N. Bastid, S. Basu, G. Batigne, B. Batyunya, D. Bauri, J. L. Bazo Alba, I. G. Bearden, C. Beattie, I. Belikov, A. D. C. Bell Hechavarria, F. Bellini, R. Bellwied, S. Belokurova, V. M. Belyaev, G. Bencédi, S. Beolè, A. Bercuci, Y. Berdnikov, Anastasia Berdnikova, D. Berényi, L. Bergmann, M.G. Besoiu, L. Betev, Partha Pratim Bhaduri, A. Bhasin, I. R. Bhat, M.A. Bhat, B. Bhattacharjee, P. Bhattacharya, A. Bianchi, L. Bianchi, N. Bianchi, J. Bielčík
Abstract
The first measurement of the cross section for coherent J / ψ photoproduction as a function of | t | , the square of the momentum transferred between the incoming and outgoing target nucleus, is presented. The data were measured with the ALICE detector in ultra-peripheral Pb–Pb collisions at a centre-of-mass energy per nucleon pair s NN = 5.02 TeV with the J / ψ produced in the central rapidity region | y | < 0.8 , which corresponds to the small Bjorken- x range ( 0.3 − 1.4 ) × 10 − 3 . The measured | t | -dependence is not described by computations based only on the Pb nuclear form factor, while the photonuclear cross section is better reproduced by models including shadowing according to the leading-twist approximation, or gluon-saturation effects from the impact-parameter dependent Balitsky–Kovchegov equation. These new results are therefore a valid tool to constrain the relevant model parameters and to investigate the transverse gluonic structure at very low Bjorken- x .