Evidence of rescattering effect in Pb–Pb collisions at the LHC through production of K⁎(892)0 and ϕ(1020) mesons

Abstract

Measurements of K⁎(892)0 and ϕ(1020) resonance production in Pb–Pb and pp collisions at √sNN = 5.02 TeV with the ALICE detector at the Large Hadron Collider are reported. The resonances are measured at midrapidity (|y| < 0.5) via their hadronic decay channels and the transverse momentum (pT) distributions are obtained for various collision centrality classes up to pT = 20 GeV/c. The pT-integrated yield ratio K⁎(892)0/K in Pb–Pb collisions shows significant suppression relative to pp collisions and decreases towards more central collisions. In contrast, the ϕ(1020)/K ratio does not show any suppression. Furthermore, the measured K⁎(892)0/K ratio in central Pb–Pb collisions is significantly suppressed with respect to the expectations based on a thermal model calculation, while the ϕ(1020)/K ratio agrees with the model prediction. These measurements are an experimental demonstration of rescattering of K⁎(892)0 decay products in the hadronic phase of the collisions. The K⁎(892)0/K yield ratios in Pb–Pb and pp collisions are used to estimate the time duration between chemical and kinetic freeze-out, which is found to be ∼ 4–7 fm/c for central collisions. The pT-differential ratios of K⁎(892)0/K, ϕ(1020)/K, K⁎(892)0/π, ϕ(1020)/π, p/K⁎(892)0 and p/ϕ(1020) are also presented for Pb–Pb and pp collisions at √sNN = 5.02 TeV. These ratios show that the rescattering effect is predominantly a low-pT phenomenon.