Results on strange hadron and resonance production in Pb–Pb collisions at the LHC with ALICE

Maria Nicassio

doi:10.1051/epjconf/20136013006

Abstract

Strange hadrons and resonances are among the most sensitive probes to investigate the characteristics of the system formed in high-energy heavy-ion collisions. The ALICE Collaboration has measured strange hadrons and meson resonances decaying into final states with charged particles. Results on the production of K (892) 0 and (1020) resonances, K 0 , , and and their anti-particles at mid-rapidity in p sNN = 2.76 TeV Pb-Pb collisions are presented and compared with those at lower energy and in proton-proton interactions. Our current understanding will be discussed focussing on particle ratios, thermal model fits to particle yields, strangeness enhancement and baryon anomaly.

Highlights

In ultra-relativistic heavy-ion collisions, when a QuarkGluon Plasma (QGP) is formed, the production of hadrons is strongly influenced by the occurrence of the deconfined state and differs from that in elementary collisions [1]
Particle yields measured by the ALICE Collaboration in different centrality intervals have been fitted with a chemical non-equilibrium implementation of the model [14]. In this implementation the phase space occupancy factors γs,q, which are additional non-equilibrium parameters introduced in some models to account for nonthermal production, are used. This approach relies on a sudden hadronization which occurs from a cool QGP (T ≈ 140 MeV) in thermal equilibrium, so that there is no significant modification of the quark abundances and they remain close to the chemical equilibrium values
Some of the main results on strangeness production in Pb–Pb collisions obtained by the ALICE Collaboration have been presented and compared to the observations at lower energies and in pp collisions

Summary

Data sample and analysis

In ultra-relativistic heavy-ion collisions, when a QuarkGluon Plasma (QGP) is formed, the production of hadrons is strongly influenced by the occurrence of the deconfined state and differs from that in elementary collisions [1]. Strange hadrons and resonances that decay into final states with charged particles only are reconstructed in ALICE. In this contribution the following main decays are covered: φ(1020) → K− + K+ and KS0 Ξ−. Integrated yields are obtained integrating the measured spectra and using fit functions to extrapolate down to zero transverse momentum.

Thermal model fit of particle yields

Strangeness enhancement

Baryon anomaly

Resonance to non-resonance ratios

Summary and conclusions