Centrality dependence of J/ψ and ψ(2S) production and nuclear modification in p-Pb collisions at $$ \sqrt{s_{\mathrm{NN}}} $$ = 8.16 TeV

The inclusive production of the J/ψ and ψ(2S) charmonium states is studied as a function of centrality in p-Pb collisions at a centre-of-mass energy per nucleon pair $$ \sqrt{s_{\mathrm{NN}}} $$ s NN = 8.16 TeV at the LHC. The measurement is performed in the dimuon decay channel with the ALICE apparatus in the centre-of-mass rapidity intervals −4.46 < ycms< −2.96 (Pb-going direction) and 2.03 < ycms< 3.53 (p-going direction), down to zero transverse momentum (pT). The J/ψ and ψ(2S) production cross sections are evaluated as a function of the collision centrality, estimated through the energy deposited in the zero degree calorimeter located in the Pb-going direction. The pT-differential J/ψ production cross section is measured at backward and forward rapidity for several centrality classes, together with the corresponding average 〈pT〉 and $$ \left\langle {p}_{\mathrm{T}}^2\right\rangle $$ p T 2 values. The nuclear effects affecting the production of both charmonium states are studied using the nuclear modification factor. In the p-going direction, a suppression of the production of both charmonium states is observed, which seems to increase from peripheral to central collisions. In the Pb-going direction, however, the centrality dependence is different for the two states: the nuclear modification factor of the J/ψ increases from below unity in peripheral collisions to above unity in central collisions, while for the ψ(2S) it stays below or consistent with unity for all centralities with no significant centrality dependence. The results are compared with measurements in p-Pb collisions at $$ \sqrt{s_{\mathrm{NN}}} $$ s NN = 5.02 TeV and no significant dependence on the energy of the collision is observed. Finally, the results are compared with theoretical models implementing various nuclear matter effects.

Investigation of centrality dependence of dynamical fluctuations in narrow pseudo-rapidity interval on event-by-event basis

A detailed study of centrality dependence of event-by-event fluctuations of maximum particle density of the produced particles in narrow pseudo-rapidity interval in terms of the scaled variance [Formula: see text] has been carried out for [Formula: see text]O-emulsion interactions at 4.5[Formula: see text]AGeV/[Formula: see text]. Depending on the values of the total charges or sum of the charges of noninteracting projectile fragments, event samples were classified into four centrality classes. Presence of event-by-event fluctuations of maximum particle density is reflected in the multiparticle production process for different centrality classes. The event-by-event fluctuations are found to decrease with the increase of pseudo-rapidity interval. The event-by-event fluctuations are found to decrease with decreasing centrality of collisions. A comparison with the analyzed results of the total disintegration events has also been carried out. Experimental analysis results have been compared with those obtained from the analysis of Monte Carlo simulated (MC-RAND) events in order to extract the dynamical fluctuations.

Z plus jets production via double parton scattering in pA collisions at the LHC

We present results on Zjj production via double parton scattering in pA collisions at the LHC. We perform the analysis at leading and next-leading order accuracy with different sets of cuts on jet transverse momenta and accounting for the single parton scattering background. By exploiting the experimental capability to measure the centrality dependence of the cross section, we discuss the feasibility of DPS observation in already collected data at the LHC and in future runs.