First Measurement of the |t| Dependence of Incoherent J/ψ Photonuclear Production

The first measurement of the cross section for incoherent photonuclear production of J/ψ vector mesons as a function of the Mandelstam |t| variable is presented. The measurement was carried out with the ALICE detector at midrapidity, |y|<0. 8, using ultraperipheral collisions of Pb nuclei at a center-of-mass energy per nucleon pair of sqrts₍₍=5. 02 TeV. This rapidity interval corresponds to a Bjorken-x range (0. 3-1. 4) ×10^-3. Cross sections are given in five |t| intervals in the range 0. 04<|t|<1 GeV^2 and compared to the predictions by different models. Models that ignore quantum fluctuations of the gluon density in the colliding hadron predict a |t| dependence of the cross section much steeper than in data. The inclusion of such fluctuations in the same models provides a better description of the data.