Excitation Functions of Tsallis-Like Parameters in High-Energy Nucleus–Nucleus Collisions

Abstract

The transverse momentum spectra of charged pions, kaons, and protons produced at mid-rapidity in central nucleus–nucleus (AA) collisions at high energies are analyzed by considering particles to be created from two participant partons, which are assumed to be contributors from the collision system. Each participant (contributor) parton is assumed to contribute to the transverse momentum by a Tsallis-like function. The contributions of the two participant partons are regarded as the two components of transverse momentum of the identified particle. The experimental data measured in high-energy AA collisions by international collaborations are studied. The excitation functions of kinetic freeze-out temperature and transverse flow velocity are extracted. The two parameters increase quickly from ≈3 to ≈10 GeV (exactly from 2.7 to 7.7 GeV) and then slowly at above 10 GeV with the increase of collision energy. In particular, there is a plateau from near 10 GeV to 200 GeV in the excitation function of kinetic freeze-out temperature.

Thermal freeze-out parameters and pseudo-entropy from charged hadron spectra in high energy collisions

“…In the above discussion, we have used a particular parameterization for the p T distribution and obtained the tendencies of parameters, but many other parameterizations are available and used in the field. Our conclusions on the behaviors of main parameters n [or q = (n+1)/n], T 0 , and β t with increasing the collision energy, event centrality, and particle mass are similar to others if one uses different parameterizations [49,50,[52][53][54][55][56][57][58], though the absolute sizes may be different. The parameter a 0 is a new one introduced by us recently [45], which is hard to compare with others at present due to the lack of related work, though the relative sizes of a 0 on particle mass are understandable.…”

“…In order to obtain the thermal or kinetic (or kinematic) freeze-out temperature T 0 and the average transverse flow velocity β t [48][49][50][51], one may fit firstly the p T spectra of particles to obtain the effective temperature T , and the average p T ( p T ) and average energy (m) of particles in the source rest frame using the Monte Carlo algorithm [52][53][54][55][56][57][58]. Then, one may extract the intercept as T 0 in the linear relation of T versus m 0 , and further obtain the slope as β t in the linear relation of p T versus m.…”

An Energy Independent Scaling of Transverse Momentum Spectra of Direct (Prompt) Photons from Two‐Body Processes in High‐Energy Proton–Proton Collisions

“…The Revised Tsallis-Like Function and the Root-Sum-of-Squares of Two Functions According to refs. [6,42,43,[60][61][62], we know that, at mid-rapidity, the Tsallis-like distribution obeyed by p T can be written as…”

“…Similar to Equation (2), in fitting the p T spectrum, Equation ( 6) is not ideal in very-low-p T region, too. Empirically, we may revise Equation (6) to the following form…”

“…[2][3][4][5] The main reason for studying high-energy heavy ion collisions is to understand the formation and properties of QGP. [6][7][8][9] High-energy proton-proton (p+p), proton-nucleus, and nucleusnucleus collisions can provide a hightemperature and/or high-density environment, which is similar to the early days of the Big Bang in the universe. [10][11][12][13] In the evolution process of high-energy collisions, [14][15][16] the chemical and kinetic freeze-outs are two very important stages.…”