Abstract
Four models for the initial conditions of a fluid dynamic description of high energy heavy ion collisions are analysed and compared. We study expectation values and event-by-event fluctuations in the initial transverse energy density profiles from Pb-Pb collisions. Specifically, introducing a Fourier-Bessel mode expansion for fluctuations, we determine expectation values and two-mode correlation functions of the expansion coefficients. The analytically solveable independent point-sources model is compared to an initial state model based on Glauber theory and two models based on the Color Glass Condensate framework. We find that the large wavelength modes of all investigated models show universal properties for central collisions and also discuss to which extent general properties of initial conditions can be understood analytically.
Highlights
Relativistic heavy-ion collisions arguably constitute one of the most spectacular physical experiments mankind is capable of conducting in a laboratory
At collider facilities like the Relativistic Heavy Ion Collider and the Large Hadron Collider (LHC), physicists focus beams of nuclei and make them collide at relativistic energies, producing thousands of new particles per nucleus-nucleus collision [1,2,3,4]
The two-mode correlation functions of Fourier-Bessel coefficients are compared to predictions of three additional initial condition models: the independent point-sources model (IPSM) of initial conditions [14,16,17,18,19]
Summary
Relativistic heavy-ion collisions arguably constitute one of the most spectacular physical experiments mankind is capable of conducting in a laboratory. The two-mode correlation functions of Fourier-Bessel coefficients are compared to predictions of three additional initial condition models: the independent point-sources model (IPSM) of initial conditions [14,16,17,18,19] This particular model assumes fluctuations to originate from independent pointshaped contributions and allows closed-form expressions for the statistical quantities of interest. It is generally expected that a fluid description which propagates (correlations of) the energy momentum tensor to the final state becomes valid only after some period of early time nonequilibrium quantum field dynamics. During such a far-from-equilibrium phase the energy-momentum tensor and its correlation function can get modified.
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