Photoproduction of low-$p_{\rm T}$ J/$\psi$ from peripheral to central Pb$-$Pb collisions at 5.02 TeV

The ALICE collaboration
Phys.Lett.B 846 (2023) 137467, 2023.

Abstract
An excess of J/$\psi$ yield at very low transverse momentum ($p_{\rm T} < 0.3$ GeV/$c$), originating from coherent photoproduction, is observed in peripheral and semicentral hadronic Pb$-$Pb collisions at a center-of-mass energy per nucleon pair of $\sqrt{s_{\rm NN}} = 5.02$ TeV. The measurement is performed with the ALICE detector via the dimuon decay channel at forward rapidity ($2.5<y<4$). The nuclear modification factor at very low $p_{\rm T}$ and the coherent photoproduction cross section are measured as a function of centrality down to the 10% most central collisions. These results extend the previous study at $\sqrt{s_{\rm NN}} = 2.76$ TeV, confirming the clear excess over hadronic production in the $p_{\rm T}$ range 0$-$0.3 GeV/$c$ and the centrality range 70$-$90%, and establishing an excess with a significance greater than 5$\sigma$ also in the 50$-$70% and 30$-$50% centrality ranges. The results are compared with earlier measurements at $\sqrt{s_{\rm NN}} = 2.76$ TeV and with different theoretical predictions aiming at describing how coherent photoproduction occurs in hadronic interactions with nuclear overlap.

  • Figure 1a

    10.17182/hepdata.134024.v1/t1

    J/$\psi$ nuclear modification factor as a function of $\langle N_{\rm part}\rangle$ measured in the rapidity range 2.5 < y <...

  • Figure 1b

    10.17182/hepdata.134024.v1/t2

    J/$\psi$ nuclear modification factor as a function of $\langle N_{\rm part} \rangle$ measured in the rapidity range 2.5 < y...

  • Figure 1c

    10.17182/hepdata.134024.v1/t3

    J/$\psi$ nuclear modification factor as a function of $\langle N_{\rm part} \rangle$ measured in the rapidity range 2.5 < y...

  • Figure 2

    10.17182/hepdata.134024.v1/t4

    J/$\psi$ coherent photoproduction cross section as a function of $\langle N_{\rm part}\rangle$ at forward rapidity in Pb–Pb collisions at $\sqrt{s_{\rm...

  • Figure 3

    10.17182/hepdata.134024.v1/t5

    J/$\psi$ coherent photoproduction cross section ratio for two different energies ($\sqrt{s_{\rm NN}}$ = 5.02 TeV over $\sqrt{s_{\rm NN}}$ = 2.76...

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