Skewness of mean transverse momentum fluctuations in heavy-ion collisions
Giuliano Giacalone, Fernando G. Gardim, Jacquelyn Noronha-Hostler, Jean-Yves Ollitrault
Abstract
We propose the skewness of mean transverse momentum $\ensuremath{\langle}{p}_{t}\ensuremath{\rangle}$ fluctuations as a fine probe of hydrodynamic behavior in relativistic nuclear collisions. We describe how the skewness of the $\ensuremath{\langle}{p}_{t}\ensuremath{\rangle}$ distribution can be analyzed experimentally, and we use hydrodynamic simulations to predict its value. We predict, in particular, that $\ensuremath{\langle}{p}_{t}\ensuremath{\rangle}$ fluctuations have positive skew, which is significantly larger than if particles were emitted independently. We elucidate the origin of this result by deriving generic formulas relating the fluctuations of $\ensuremath{\langle}{p}_{t}\ensuremath{\rangle}$ to the fluctuations of the early-time thermodynamic quantities. We postulate that the large positive skewness of $\ensuremath{\langle}{p}_{t}\ensuremath{\rangle}$ fluctuations is a generic prediction of hydrodynamic models.