Fluctuating flow angles and anisotropic flow measurements

TL;DR

This paper investigates how initial density fluctuations in heavy-ion collisions cause event-by-event variations in flow angles and their transverse momentum dependence, impacting flow measurements and providing insights into the initial state and medium properties.

Contribution

It demonstrates that flow angle fluctuations lead to distinct transverse momentum dependencies in flow coefficients, enabling experimental constraints on initial state fluctuations and medium viscosity.

Findings

Flow angle fluctuations cause measurable differences in flow coefficients.

Transverse momentum dependencies reveal initial density inhomogeneities.

Flow measurements can constrain shear viscosity of the medium.

Abstract

Event-by-event fluctuations in the initial density distributions of the fireballs created in relativistic heavy-ion collisions lead to event-by-event fluctuations of the final anisotropic flow angles, and density inhomogeneities in the initial state cause these flow angles to vary with the transverse momentum of the emitted particles. It is shown that these effects lead to characteristically different transverse momentum dependencies for anisotropic flow coefficients extracted from different experimental methods. These differences can be used to experimentally constrain flow angle fluctuations in the final state of heavy-ion collisions which, in turn, are sensitive to the initial state density fluctuations and the shear viscosity of the expanding fireball medium.