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Title: Effects of fluctuations on the initial eccentricity from the color glass condensate in heavy ion collisions

Abstract

We introduce a modified form of the Kharzeev-Levin-Nardi (KLN) approach for nuclear collisions. The new ansatz for the unintegrated gluon distribution function preserves factorization, and the saturation scale is bound from below by that for a single nucleon. It also reproduces the correct scaling with the number of collisions at high transverse momentum. The corresponding Monte Carlo implementation allows us to account for fluctuations of the hard sources (nucleons) in the transverse plane. We compute various definitions of the eccentricity within the new approach, which are relevant for the interpretation of the elliptic flow. Our approach predicts breaking of the scaling of the eccentricity with the Glauber eccentricity at the level of about 30%.

Authors:
 [1];  [2]
  1. Frankfurt Institute for Advanced Studies (FIAS), Johann Wolfgang Goethe-Universitaet, Max-von-Laue-Str. 1, D-60438 Frankfurt (Germany)
  2. Institut fuer Theoretische Physik, Johann Wolfgang Goethe-Universitaet, Max-von-Laue-Str. 1, D-60438 Frankfurt (Germany)
Publication Date:
OSTI Identifier:
20995154
Resource Type:
Journal Article
Resource Relation:
Journal Name: Physical Review. C, Nuclear Physics; Journal Volume: 75; Journal Issue: 3; Other Information: DOI: 10.1103/PhysRevC.75.034905; (c) 2007 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
73 NUCLEAR PHYSICS AND RADIATION PHYSICS; COLLISIONS; CONDENSATES; DISTRIBUTION FUNCTIONS; FLUCTUATIONS; GLASS; GLUONS; HEAVY ION REACTIONS; MONTE CARLO METHOD; NUCLEONS; QUARK MATTER; SCALING; TRANSVERSE MOMENTUM

Citation Formats

Drescher, Hans-Joachim, and Nara, Yasushi. Effects of fluctuations on the initial eccentricity from the color glass condensate in heavy ion collisions. United States: N. p., 2007. Web. doi:10.1103/PHYSREVC.75.034905.
Drescher, Hans-Joachim, & Nara, Yasushi. Effects of fluctuations on the initial eccentricity from the color glass condensate in heavy ion collisions. United States. doi:10.1103/PHYSREVC.75.034905.
Drescher, Hans-Joachim, and Nara, Yasushi. Thu . "Effects of fluctuations on the initial eccentricity from the color glass condensate in heavy ion collisions". United States. doi:10.1103/PHYSREVC.75.034905.
@article{osti_20995154,
title = {Effects of fluctuations on the initial eccentricity from the color glass condensate in heavy ion collisions},
author = {Drescher, Hans-Joachim and Nara, Yasushi},
abstractNote = {We introduce a modified form of the Kharzeev-Levin-Nardi (KLN) approach for nuclear collisions. The new ansatz for the unintegrated gluon distribution function preserves factorization, and the saturation scale is bound from below by that for a single nucleon. It also reproduces the correct scaling with the number of collisions at high transverse momentum. The corresponding Monte Carlo implementation allows us to account for fluctuations of the hard sources (nucleons) in the transverse plane. We compute various definitions of the eccentricity within the new approach, which are relevant for the interpretation of the elliptic flow. Our approach predicts breaking of the scaling of the eccentricity with the Glauber eccentricity at the level of about 30%.},
doi = {10.1103/PHYSREVC.75.034905},
journal = {Physical Review. C, Nuclear Physics},
number = 3,
volume = 75,
place = {United States},
year = {Thu Mar 15 00:00:00 EDT 2007},
month = {Thu Mar 15 00:00:00 EDT 2007}
}
  • In this Rapid Communication, we determine the fluctuations of the initial eccentricity in heavy-ion collisions caused by fluctuations of the nucleon configurations. This is done via a Monte Carlo implementation of a color glass condensate k{sub t}-factorization approach. The eccentricity fluctuations are found to nearly saturate elliptic flow fluctuations measured recently at RHIC. Extrapolations to LHC energies are shown.
  • The eccentricity in coordinate space at midrapidity of the overlap zone in high-energy heavy-ion collisions predicted by the k{sub perpendicular}-factorization formalism is generically larger than expected from scaling with the number of participants. We provide a simple qualitative explanation of the effect which shows that it is not caused predominantly by edge effects. We also show that it is quite insensitive to 'details' of the unintegrated gluon distribution functions such as the presence of leading-twist shadowing and of an extended geometric scaling window. The larger eccentricity increases the azimuthal asymmetry of high transverse momentum particles. Finally, we point out thatmore » the longitudinal structure of the color glass condensate initial condition for hydrodynamics away from midrapidity is nontrivial but requires understanding of large-x effects.« less
  • Recent estimates that color glass condensate initial conditions may generate a larger initial eccentricity for noncentral relativistic heavy ion collisions (relative to the initial eccentricity assumed in earlier hydrodynamic calculations) have raised the possibility of a higher bound on the viscosity of the qark gluon plasma. We show that this large initial eccentricity results in part from a definition of the saturation scale as proportional to the number of nucleons participating in the collision. A saturation scale proportional to the nuclear thickness function (and therefore independent of the probe) leads to a smaller eccentricity, albeit still larger than the valuemore » used in hydrodynamic models. Our results suggest that the early elliptic flow in heavy ion collisions (unlike multiplicity distributions) is sensitive to the universality of the saturation scale in high-energy QCD.« less
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