Freeze-out scenarios in small systems at RHIC and LHC energies

We study the hadronic yields produced in two small collision systems d - Au at root s(NN) = 0.2 TeV and p - Pb at root s(NN) = 5.02 TeV, and extracted the chemical freeze-out (CFO) parameters. The CFO parameters are obtained using a hadron resonance gas (HRG) model and in this study present the system size dependence of the parameters. We observe that with the strangeness suppression factor gamma s included in the model, a single freeze-out scenario can describe hadronic yields for all the centralities of d - Au collision at root s(NN) = 0.2TeV, indicating that the strange hadrons have not reached full equilibrium. On the other hand, for small average charged particle multiplicity (< dN(ch)/d eta >) bins of p - Pb collision at root s(NN) = 5.02 TeV strangeness is not fully equilibrated whereas strangeness equilibration seems to be reached in large < dN(ch)/d eta >. For both the collision systems, no significant system volume dependence of the temperature has been observed. However, in comparable < dN(ch)/d eta > values, temperatures are 10-20 MeV larger for d - Au collision compared to p - Pb collision. We observe that the volume of the system at the CFO increases with increase of charge multiplicity for both the collisions. The increase is much steeper in p - Pb collision at root s(NN) = 5.02 TeV than d - Au collision at root s(NN) = 0.2TeV. Further, we analyze the transverse momentum (pT) spectra of different hadrons produced in d - Au collision at root s(NN) = 0.2TeV in a combined freeze-out scenario. We show the < dN(ch)/d eta > dependence of freeze-out parameters. It is observed that with gamma s included in the model, a single freeze-out scheme can describe the pT spectra. For similar < dN(ch)/d eta > values, gamma s in both the collision systems are close to each other and overall values of gamma s increase with increase of < dN(ch)/d eta >. Unlike CFO scenario using the produced hadron yields only, freeze-out temperature in combined scenario of chemical and kinetic freeze-out, obtained from pT spectra, increases with increase of < dN(ch)/d eta >. For smaller < dN(ch)/d eta > values, the temperature in d - Au collision at root s(NN) = 0.2TeV is similar to that of p - Pb collision at root s(NN) = 5.02 TeV. However, temperatures are larger in d - Au collision than p - Pb collision at larger < dN(ch)/d eta > values.