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

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/cfor central collisions. The pT- differential ratios of K* (892)^0/K, φ(1020)/K, K*(892)^0/π, φ(1020)/ π, p/K*(892)^0and 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.

Pb-Pb, K* meson, ϕ(1020) mesons, rescattering effect

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