Impact of multiplicity fluctuations on entropy scaling across system size

Abstract

The initial state is one of the greatest uncertainties in heavy-ion collisions. A model-agnostic approach is taken in the phenomenological Trento framework which constrains parameters using Bayesian analysis. However, the color-glass condensate (CGC) effective theory predicts initial energy densities that lie outside the recent Bayesian analyses due, in part, to the assumption in Trento of event-by-event multiplicity fluctuations following a $\Gamma$ distribution. We compare the Trento-preferred $\sqrt{T_{A}T_{B}}$ scaling to CGC-like $T_{A}T_{B}$ scaling coupled with log-normal fluctuations in $AuAu$ and $dAu$ collisions and find there is a significant impact on the multiplicity distributions and on the eccentricities, which may affect the extraction of viscosity in small systems.