engleski

First measurement of the |t|-dependence of coherent J/ψ photonuclear production

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 sNN=5.02TeV 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 .

J/psi(3100): photoproduction ; impact parameter: dependence ; nucleus: form factor ; nucleus: target ; nucleon: pair ; heavy ion: scattering ; coherence ; Balitsky-Kovchegov equation ; shadowing ; rapidity ; ALICE ; experimental results ; 5020 GeV-cms/nucleon

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