Abstract
The first measurement of the production of pions, kaons, (anti-)protons and phi mesons at midrapidity in Xe–Xe collisions at sqrt{s_{mathrm{NN}}} = 5.44~text {TeV} is presented. Transverse momentum (p_{mathrm{T}}) spectra and p_{mathrm{T}}-integrated yields are extracted in several centrality intervals bridging from p–Pb to mid-central Pb–Pb collisions in terms of final-state multiplicity. The study of Xe–Xe and Pb–Pb collisions allows systems at similar charged-particle multiplicities but with different initial geometrical eccentricities to be investigated. A detailed comparison of the spectral shapes in the two systems reveals an opposite behaviour for radial and elliptic flow. In particular, this study shows that the radial flow does not depend on the colliding system when compared at similar charged-particle multiplicity. In terms of hadron chemistry, the previously observed smooth evolution of particle ratios with multiplicity from small to large collision systems is also found to hold in Xe–Xe. In addition, our results confirm that two remarkable features of particle production at LHC energies are also valid in the collision of medium-sized nuclei: the lower proton-to-pion ratio with respect to the thermal model expectations and the increase of the phi -to-pion ratio with increasing final-state multiplicity.
Highlights
The production of hadrons consisting of light flavour quarks (u, d, and s) has been extensively studied in pp, p–Pb and Pb–Pb collisions at LHC energies [1,2,3,4,5,6,7,8,9,10,11] with the aim to explore the strongly interacting Quark-Gluon Plasma (QGP) produced in heavy-ion collisions
The pT distributions of π ±, K±, p and p are obtained by correcting the raw spectra for particle identification (PID) efficiency, misidentification probability, acceptance and tracking efficiencies as performed in [26] for the Inner Tracking System (ITS), Time Projection Chamber (TPC), Time Of Flight (TOF) and kink analyses
The uncertainties for track selection refer to the quality requirements based on the number of crossed rows in the TPC, the number of clusters in the ITS, the DCAxy and DCAz, and the χ 2/NDF of the reconstructed tracks
Summary
The production of hadrons consisting of light flavour quarks (u, d, and s) has been extensively studied in pp, p–Pb and Pb–Pb collisions at LHC energies [1,2,3,4,5,6,7,8,9,10,11] with the aim to explore the strongly interacting Quark-Gluon Plasma (QGP) produced in heavy-ion collisions. The good separation power obtained at low momentum is one of the key features for the measurements reported in this article reduce the contamination from secondary particles from weak decays and interactions in the detector material, as well as tracks with wrongly associated hits, similar selection criteria as described in [26,34] are used and are summarised below Tracks reconstructed with both the TPC and the ITS are required to cross at least 70 TPC readout rows out of a maximum of 159 with a χ 2 normalised to the number of TPC space points (“clusters”), χ 2/cluster, lower than 4.
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