Universal scaling of meson and baryon spectra in p-Pb collisions at 5.02TeV

Abstract

We systematically investigate the scaling property of mesons (pions and kaons) and baryons (protons, [Formula: see text], [Formula: see text] and [Formula: see text]) transverse momentum ([Formula: see text]) spectra at different centrality classes (0–5[Formula: see text], 5–10[Formula: see text], 10–20[Formula: see text], 20–40[Formula: see text], 40–60[Formula: see text], 60–80[Formula: see text] and 80–100[Formula: see text]) in proton-lead collisions with center of mass energy per nucleon pair 5.02[Formula: see text]TeV. In the low [Formula: see text] region with [Formula: see text][Formula: see text]GeV/c, a universal scaling independent of the centrality is observed in the pion (kaon, proton, [Formula: see text], [Formula: see text] and [Formula: see text]) spectra when a dilatation, [Formula: see text], is applied. Here, [Formula: see text] is a scaling parameter depending on the centrality class. We find that the rates at which ln[Formula: see text] changes with the logarithmic value of the average value of the number of participating nucleons, ln[Formula: see text], are stronger for baryons than those for mesons. In the high [Formula: see text] region, there is a deviation from the scaling. The more peripheral the collisions are, the more obvious the violation of the scaling is. In the framework of the color string percolation (CSP) model, we show that mesons and baryons are generated from the decay of clusters formed by strings overlapping in the transverse plane with the same size dispersion but with different mean size. The mean size of clusters for baryons is smaller than that of mesons. For the same hadrons at different centrality classes, the mean size of clusters decreases with the increase of centrality. The fragmentation functions for cluster decay are different for different hadrons, while they are universal for the same hadrons at different centrality classes. The universal scaling of the meson and baryon spectra in the low [Formula: see text] region can be quantitatively understood with the CSP model at the same time.