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Title: ELLIPTIC FLOW, INITIAL ECCENTRICITY AND ELLIPTIC FLOW FLUCTUATIONS IN HEAVY ION COLLISIONS AT RHIC.

Abstract

We present measurements of elliptic flow and event-by-event fluctuations established by the PHOBOS experiment. Elliptic flow scaled by participant eccentricity is found to be similar for both systems when collisions with the same number of participants or the same particle area density are compared. The agreement of elliptic flow between Au+Au and Cu+Cu collisions provides evidence that the matter is created in the initial stage of relativistic heavy ion collisions with transverse granularity similar to that of the participant nucleons. The event-by-event fluctuation results reveal that the initial collision geometry is translated into the final state azimuthal particle distribution, leading to an event-by-event proportionality between the observed elliptic flow and initial eccentricity.

Authors:
; ; ; ; ; ;
Publication Date:
Research Org.:
Brookhaven National Lab. (BNL), Upton, NY (United States)
Sponsoring Org.:
Doe - Office Of Science
OSTI Identifier:
921929
Report Number(s):
BNL-79569-2007-CP
R&D Project: 08861; KB-02-01-021; TRN: US0800830
DOE Contract Number:
DE-AC02-98CH10886
Resource Type:
Conference
Resource Relation:
Conference: LAKE LOUISE WINTER INSTITUTE 2007; ALBERTA, CANADA; 20070219 through 20070224
Country of Publication:
United States
Language:
English
Subject:
43 PARTICLE ACCELERATORS; DISTRIBUTION; FLUCTUATIONS; GEOMETRY; HEAVY IONS; NUCLEONS; BROOKHAVEN RHIC

Citation Formats

NOUICER,R., ALVER, B., BACK, B.B., BAKER, M.D., BALLINTIJN, M., BARTON, D.S., and ET AL.. ELLIPTIC FLOW, INITIAL ECCENTRICITY AND ELLIPTIC FLOW FLUCTUATIONS IN HEAVY ION COLLISIONS AT RHIC.. United States: N. p., 2007. Web.
NOUICER,R., ALVER, B., BACK, B.B., BAKER, M.D., BALLINTIJN, M., BARTON, D.S., & ET AL.. ELLIPTIC FLOW, INITIAL ECCENTRICITY AND ELLIPTIC FLOW FLUCTUATIONS IN HEAVY ION COLLISIONS AT RHIC.. United States.
NOUICER,R., ALVER, B., BACK, B.B., BAKER, M.D., BALLINTIJN, M., BARTON, D.S., and ET AL.. Mon . "ELLIPTIC FLOW, INITIAL ECCENTRICITY AND ELLIPTIC FLOW FLUCTUATIONS IN HEAVY ION COLLISIONS AT RHIC.". United States. doi:. https://www.osti.gov/servlets/purl/921929.
@article{osti_921929,
title = {ELLIPTIC FLOW, INITIAL ECCENTRICITY AND ELLIPTIC FLOW FLUCTUATIONS IN HEAVY ION COLLISIONS AT RHIC.},
author = {NOUICER,R. and ALVER, B. and BACK, B.B. and BAKER, M.D. and BALLINTIJN, M. and BARTON, D.S. and ET AL.},
abstractNote = {We present measurements of elliptic flow and event-by-event fluctuations established by the PHOBOS experiment. Elliptic flow scaled by participant eccentricity is found to be similar for both systems when collisions with the same number of participants or the same particle area density are compared. The agreement of elliptic flow between Au+Au and Cu+Cu collisions provides evidence that the matter is created in the initial stage of relativistic heavy ion collisions with transverse granularity similar to that of the participant nucleons. The event-by-event fluctuation results reveal that the initial collision geometry is translated into the final state azimuthal particle distribution, leading to an event-by-event proportionality between the observed elliptic flow and initial eccentricity.},
doi = {},
journal = {},
number = ,
volume = ,
place = {United States},
year = {Mon Feb 19 00:00:00 EST 2007},
month = {Mon Feb 19 00:00:00 EST 2007}
}

Conference:
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  • We study effects of eccentricity fluctuations on the elliptic flow coefficient v{sub 2} at midrapidity in both Au+Au and Cu+Cu collisions at {radical}(s{sub NN})=200 GeV by using a hybrid model that combines ideal hydrodynamics for space-time evolution of the quark gluon plasma phase and a hadronic transport model for the hadronic matter. For initial conditions in hydrodynamic simulations, both the Glauber model and the color glass condensate model are employed to demonstrate the effect of initial eccentricity fluctuations originating from the nucleon position inside a colliding nucleus. The effect of eccentricity fluctuations is modest in semicentral Au+Au collisions, but significantlymore » enhances v{sub 2} in Cu+Cu collisions.« less
  • 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 themore » scaling of the eccentricity with the Glauber eccentricity at the level of about 30%.« less
  • A new method is presented for determining event-by-event fluctuations of elliptic flow, v{sub 2}, using first-order event planes. By studying the event-by-event distributions of v{sub 2} observables and first-order event-plane observables, average flow <v{sub 2}> and event-by-event flow fluctuations can be separately determined, making appropriate allowance for the effects of finite multiplicity and nonflow. The method has been tested with Monte Carlo simulations. The connection between flow fluctuations and fluctuations of the initial-state participant eccentricity is discussed.
  • We analyze the recently measured v{sub 2} fluctuation in the context of establishing the degree of fluidity of the matter produced in heavy ion collisions. We argue that flow observables within systems with a non-negligible mean free path should acquire a 'dynamical' fluctuation, due to the random nature of each collision between the system's degrees of freedom. Because of this, v{sub 2} fluctuations can be used to estimate the Knudsen number of the system produced at the Relativistic Heavy Ion Collider (RHIC). To illustrate this quantitatively, we apply the UrQMD model, with scaled cross sections, to show that collisions atmore » RHIC have a Knudsen number at least one order of magnitude below the expected value for an interacting hadron gas. Furthermore, we argue that the Knudsen number is also bound from below by the v{sub 2} fluctuation data, because too small a Knudsen number would break the observed scaling of v{sub 2} fluctuations due to the onset of turbulent flow. We propose, therefore that v{sub 2} fluctuation measurements, together with an understanding of the turbulent regime for relativistic hydrodynamics, will provide an upper as well as a lower limit for the Knudsen number. We also argue that an energy scan of v{sub 2} fluctuations could shed light on the onset of the fluid regime.« less
  • We present a number of independent flow observables that can be measured using multiparticle azimuthal correlations in heavy-ion collisions. Some of these observables are already well known, such as v{sub 2}(2) and v{sub 2}(4), but most are new--in particular, joint correlations among v{sub 1}, v{sub 2}, and v{sub 3}. Taken together, these measurements will allow for a more precise determination of the medium properties than is currently possible. In particular, by taking ratios of these observables, we construct quantities that are less sensitive to the hydrodynamic response of the medium and thus more directly characterize the initial-state fluctuations of themore » event shape, which may constrain models for early-time, nonequilibrium QCD dynamics. We present predictions for these ratios using two Monte Carlo models and compare them to available data.« less