# Role of system size in freeze-out conditions extracted from transverse momentum spectra of hadrons

Dash, Ajay Kumar (School of Physical Sciences, National Institute of Science Education and Research, HBNI, Jatni 752050, India) ; Singh, Ranbir (School of Physical Sciences, National Institute of Science Education and Research, HBNI, Jatni 752050, India) ; Chatterjee, Sandeep (AGH University of Science and Technology, Faculty of Physics and Applied Computer Science, al. Mickiewicza 30, 30-059 Krakow, Poland and Department of Physical Sciences, Indian Institute of Science Education and Research, Berhampur, Transit Campus, Government ITI, Berhampur 760010, Odisha, India) ; Jena, Chitrasen (Indian Institute of Science Education and Research, Tirupati 517507, India) ; Mohanty, Bedangadas (School of Physical Sciences, National Institute of Science Education and Research, HBNI, Jatni 752050, India)

05 December 2018

Abstract: The data on hadron transverse momentum spectra in different centrality classes of p + Pb collisions at $\sqrt{{s}_{\mathrm{NN}}}=5.02$ TeV have been analyzed to extract the freeze-out hypersurface within a simultaneous chemical and kinetic freeze-out scenario. The freeze-out hypersurface has been extracted for three freeze-out schemes that differ in the way strangeness is treated: (i) unified freeze-out for all hadrons at complete thermal equilibrium (1FO), (ii) unified freeze-out for all hadrons with an additional parameter ${\gamma }_{S}$ which accounts for possible out-of-equilibrium production of strangeness ($1\mathrm{FO}+{\gamma }_{S}$), and (iii) separate freeze-out for hadrons with and without strangeness content (2FO). Unlike in heavy-ion collisions where 2FO performs best in describing the mean hadron yields as well as the transverse momentum spectra, with p + Pb we find that $1\mathrm{FO}+{\gamma }_{S}$ with one fewer parameter than 2FO performs better. This confirms expectations based on previous analysis of system size dependence in the freeze-out scheme with mean hadron yields: while heavy-ion collisions that are dominated by constituent interactions prefer 2FO, smaller collision systems like proton + nucleus and proton + proton collisions with lesser constituent interaction prefer a unified freeze-out scheme with varying degrees of strangeness equilibration.

Published in: Physical Review C 98 (2018)