Centrality dependence of strange particle production in Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV

Abstract

The centrality dependence of strange (K${}_S^0$, $\Lambda +\bar{\Lambda }$) and multi-strange (${\Xi }^{-}+\overline{{\Xi }^{+}}$, ${\Omega }^{-}+{\bar{\Omega }}^{+}$) hadron production is measured by ALICE in the LHC lead$-$lead (Pb$-$Pb) collisions at a center-of-mass energy per nucleon pair $\sqrt{s_{\mathrm{NN}}}=5.02$ TeV, using the full data set collected during the LHC Run 2 campaign in the years 2015 and 2018. This is the largest heavy$-$ion data set analyzed to date at the LHC, and it allows for the extraction of transverse momentum ($p_T$) spectra and $p_T$-integrated yields with unprecedented precision, over a broad range of charged particle multiplicity densities ($⟨d{N}_{ch}/d\eta {⟩}_{|\eta |<0.5}$), probing regions where smaller collision system (pp and p$-$Pb) results are also available. The $p_T$ spectra evolve with centrality, featuring higher $⟨p_T⟩$ in central events for all particles. The $\Lambda /$K${}_S^0$ ratio exhibits the distinctive baryon-to-meson enhancement in the intermediate $p_T$ region, with a maximum which is shifted to larger $p_T$ for more central collisions. The hadron-to-pion yield ratios are presented as a function of $⟨d{N}_{ch}/d\eta {⟩}_{|\eta |<0.5}$ and compared to results from different collision systems and energies. A smooth connection from pp to Pb$-$Pb is observed, thus demonstrating that collision system or energy do not play a role in the multiplicity evolution of this observable. The previously reported enhancement of strangeness production in the multiplicity range probed in pp and p$-$Pb collisions saturates in the multiplicity range of Pb$-$Pb data. These results constitute a key test bench for theoretical models and a first comparison to the EPOS 4 generator is presented.

arXiv comment26 pages, 5 captioned figures, 2 tables, authors from page 20, published version, figures at http://alice-publications.web.cern.ch/node/12794