Abstract
The event-shape and multiplicity dependence of the chemical freeze-out temperature (Tch), freeze-out radius (R), and strangeness saturation factor (γs) are obtained by studying the particle yields from the PYTHIA8 Monte Carlo event generator in proton-proton (pp) collisions at the centre-of-mass s = 13 TeV. Spherocity is one of the transverse event-shape techniques to distinguish jetty and isotropic events in high-energy collisions and helps in looking into various observables in a more differential manner. In this study, spherocity classes are divided into three categories, namely (i) spherocity integrated, (ii) isotropic, and (iii) jetty. The chemical freeze-out parameters are extracted using a statistical thermal model as a function of the spherocity class and charged particle multiplicity in the canonical, strangeness canonical, and grand canonical ensembles. A clear observation of the multiplicity and spherocity class dependence of Tch, R, and γs is observed. A final state multiplicity, Nch≥ 30 in the forward multiplicity acceptance of the ALICE detector appears to be a thermodynamic limit, where the freeze-out parameters become almost independent of the ensembles. This study plays an important role in understanding the particle production mechanism in high-multiplicity pp collisions at the Large Hadron Collider (LHC) energies in view of a finite hadronic phase lifetime in small systems.
Highlights
Quark Gluon Plasma (QGP), a deconfined state of quarks and gluons, is believed to be produced in heavy-ion collisions at the Relativistic Heavy-Ion Collider (RHIC) and the Large Hadron Collider (LHC).the observations of QGP signatures like the strangeness enhancement [1] and double ridge structure [2] in high-multiplicity proton-proton collisions at the LHC indicate the possible formation of QGP droplets in pp collisions
QGP-like behaviours have been successfully explained by phenomena such as multi-partonic interactions, string fragmentation, color reconnection, rope hadronization, etc., which are incorporated in the PYTHIA8
In this study, (π + + π − )/2, (K+ + K− )/2, (p + p)/2, φ, and (Λ + Λ)/2 yields at mid-rapidity obtained from PYTHIA8 are used to extract the chemical freeze-out (CFO) parameters in THERMUS [21] based on the canonical, strangeness canonical, and grand canonical ensembles
Summary
Quark Gluon Plasma (QGP), a deconfined state of quarks and gluons, is believed to be produced in heavy-ion collisions at the Relativistic Heavy-Ion Collider (RHIC) and the Large Hadron Collider (LHC). Unlike the lower collision energies, where pp has been used as a reference measurement to study heavy-ion collisions, the pp collisions at the LHC energies have brought up new challenges and opportunities in terms of their high-multiplicity environment to study many emergent phenomena In this direction, one uses the recently introduced transverse spherocity to separate jetty and isotropic events in pp collisions, as the production dynamics for both are different. The present study should serve as a baseline work in this direction exploring the CFO properties in pp collisions and their event topology and multiplicity dependence This need arises because of the different dynamics of particle production in jetty and isotropic events.
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