# 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.

## Key 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.

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Source: https://tomesphere.com/paper/1703.04944