Kinetic freeze-out temperatures in central and peripheral collisions: Which one is larger?

TL;DR

This study compares various methods to extract kinetic freeze-out temperatures in nucleus-nucleus collisions at RHIC and LHC, revealing that central collisions generally have higher freeze-out temperatures than peripheral ones.

Contribution

It systematically evaluates four different extraction methods and clarifies the impact of transverse flow velocity assumptions on the temperature results.

Findings

Central collisions have higher freeze-out temperatures than peripheral collisions.

The choice of transverse flow velocity significantly affects temperature estimates.

Re-examining flow velocity assumptions resolves contradictions among methods.

Abstract

The kinetic freeze-out temperatures, $T_0$, in nucleus-nucleus collisions at the Relativistic Heavy Ion Collider (RHIC) and Large Hadron Collider (LHC) energies are extracted by four methods: i) the Blast-Wave model with Boltzmann-Gibbs statistics (the BGBW model), ii) the Blast-Wave model with Tsallis statistics (the TBW model), iii) the Tsallis distribution with flow effect (the improved Tsallis distribution), and iv) the intercept in $T=T_0+am_0$ (the alternative method), where $m_0$ denotes the rest mass and $T$ denotes the effective temperature which can be obtained by different distribution functions. It is found that the relative sizes of $T_0$ in central and peripheral collisions obtained by the conventional BGBW model which uses a zero or nearly zero transverse flow velocity, $\beta_T$, are contradictory in tendency with other methods. With a re-examination for $\beta_T$ in the first method in which $\beta_T$ is taken to be $\sim(0.40\pm0.07)c$, a recalculation presents a consistent result with others. Finally, our results show that the kinetic freeze-out temperature in central collisions is larger than that in peripheral collisions.