Multi-strange baryon production in pp, p–Pb and Pb–Pb collisions measured with ALICE

Domenico Colella

doi:10.1051/epjconf/20148000033

Abstract

The production of {\Xi}$^{-}$ and {\Omega}$^{-}$ baryons and their anti-particles in pp, p-Pb and Pb-Pb collisions has been measured by the ALICE Collaboration. These hyperons are reconstructed via the detection of their charged weak-decay products, which are identified through their measured ionisation losses and momenta in the ALICE Time Projection Chamber. Comparing the production yields in Pb-Pb and pp collisions, a strangeness enhancement has been measured and found to increase with the centrality of the collision and with the strangeness content of the baryon; moreover, in the comparison with similar measurements at lower energies, it decreases as the centre-of-mass energy increases, following the trend already observed moving from SPS to RHIC. Recent measurement of cascade and {\Omega} in p-Pb interactions are compared with results in Pb-Pb and pp collisions and with predictions from thermal models, based on a grand canonical approach. The nuclear modification factors for the charged {\Xi} and {\Omega}, compared to the ones for the lighter particles, are also presented.

Highlights

Measuring strange and multi-strange particle production in relativistic heavy-ion interactions is a unique tool to investigate the properties of the hot and dense matter created in the collision, as there is no net strangeness content in the initially colliding nuclei
Comparing the production yields in Pb–Pb and pp collisions, a strangeness enhancement has been measured and found to increase with the centrality of the collision and with the strangeness content of the baryon; in the comparison with similar measurements at lower energies, it decreases as the centre-of-mass energy increases, following the trend already observed moving from SPS to RHIC
The production of the multi-strange baryons Ξ− and Ω− and their antiparticles have been measured by the ALICE Collaboration in pp, p–Pb and Pb–Pb collisions

Summary

Introduction

Measuring strange and multi-strange particle production in relativistic heavy-ion interactions is a unique tool to investigate the properties of the hot and dense matter created in the collision, as there is no net strangeness content in the initially colliding nuclei. Strangeness enhancement in heavy-ion collisions with respect to pp (p–Be) has been observed in Pb–Pb collisions at the NA57 experiment [2], at STAR [3] in Au–Au collisions, and confirmed by ALICE in central 2.76 TeV Pb–Pb collisions [4] EPJ Web of Conferences factor (RAA) as a function of pT measured in Pb–Pb collisions at the LHC [6], is interpreted as the result of the energy loss suffered by partons when traversing the hot and dense matter created in an ultra-relativistic heavy-ion collision. The larger suppression observed at LHC compared to that at RHIC can be explained by the higher density of the medium created in collisions at higher centre-ofmass energy

Multi-strange decay reconstruction with the ALICE detector

Strangeness enhancements

Multi-strange nuclear modification factors

Conclusions