# Size fluctuations of the initial source and the event-by-event transverse momentum fluctuations in relativistic heavy-ion collisions

## TL;DR

This paper demonstrates that initial size fluctuations in relativistic heavy-ion collisions, modeled via Glauber and hydrodynamic simulations, can explain the observed event-by-event transverse momentum fluctuations at RHIC.

## Contribution

It introduces a comprehensive model linking initial size fluctuations to transverse momentum fluctuations, matching experimental data.

## Key findings

- Initial size fluctuations cause measurable p_T fluctuations.
- Hydrodynamic evolution translates size fluctuations into momentum fluctuations.
- Model reproduces centrality and energy dependence observed in experiments.

## Abstract

We show that the event-by-event fluctuations of the transverse size of the initial source, which follow directly from the Glauber treatment of the earliest stage of relativistic heavy-ion collisions, cause, after hydrodynamic evolution, fluctuations of the transverse flow velocity at hadronic freeze-out. This in turn leads to event-by-event fluctuations of the average transverse momentum, p_T. Simulations with GLISSANDO for the Glauber phase, followed by a realistic hydrodynamic evolution and statistical hadronization carried out with THERMINATOR, lead to agreement with the RHIC data. In particular, the magnitude of the effect, its centrality dependence, and the weak dependence on the incident energy are properly reproduced. Our results show that bulk of the observed event-by-event p_T fluctuations may be explained by the fluctuations of the size of the initial source.