Abstract
We apply stochastic hydrodynamics to the study of charge density fluctuations in QCD matter undergoing Bjorken expansion. We find that the charge density correlations are given by a time integral over the history of the system, with the dominant contribution coming from the QCD crossover region where the change of susceptibility per entropy, chi T/s, is most significant. We study the rapidity and azimuthal angle dependence of the resulting charge balance function using a simple analytic model of heavy-ion collision evolution. Our results are in agreement with experimental measurements, indicating that hydrodynamic fluctuations contribute significantly to the measured charge correlations in high energy heavy-ion collisions. The sensitivity of the balance function to the value of the charge diffusion coefficient D allows us to estimate the typical value of this coefficient in the crossover region to be rather small, of the order of 1/(2pi T), characteristic of a strongly coupled plasma.
Highlights
Event-by-event fluctuations and two particle correlations [1] in high-energy heavy-ion collision experiments provide valuable information about the collective dynamics: thermal and transport properties of the hot and dense QCD matter
We find that the charge-density correlations are given by a time integral over the history of the system, with the dominant contribution coming from the QCD crossover region where the change of susceptibility per entropy, χ T /s, is most significant
Much recent effort has been devoted to the measurement and understanding of the correlations observed at the Relativistic Heavy Ion Collider (RHIC) and the Large Hadron Collider (LHC)
Summary
Event-by-event fluctuations and two particle correlations [1] in high-energy heavy-ion collision experiments provide valuable information about the collective dynamics: thermal and transport properties of the hot and dense QCD matter. We apply relativistic stochastic hydrodynamics [14] to study the balance functions in heavy-ion collisions. In order to describe fluctuations around a nonstatic solution of the hydrodynamic equations (such as, e.g., Bjorken expansion) one can introduce local noise into the hydrodynamic equations, as has been proposed by Landau and Lifshitz [15] but has only recently been applied in the context of relativistic heavy-ion collisions [14]. II E, we use the lattice QCD data [17,18] to obtain the dependence of susceptibility per entropy χ T /s on temperature which determines the magnitude of the charge correlations
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