Pseudorapidity shape of elliptic flow as signature for fast equilibration in relativistic heavy-ion collisions at energies up tosNN=200GeV

Abstract

The implications of parton recombination processes on the dynamics of ultrarelativistic heavy-ion reactions are investigated. To do so, the quark-gluon string transport model has been extended for partonic recombination and fusion processes. Parton recombination leads to short equilibration times and improves significantly on the theoretical description of measured directed and elliptic flow, i.e., v1 and v2, distributions in Au+Au collisions at √ sNN = 200 GeV, in particular what concerns their pseudorapidity dependence. The shape of v2(η) is found to be closely related to fast thermalization.

Directed flow measurements from STAR

“…together with five model calculations, namely, RQMD [9], UrQMD [13], AMPT [14], QGSM with parton recombination [15], and hydrodynamic calculation with a tilted source [8]. Many model calculations either predict wrong sign of pions v 1 or wrong magnitude.…”

“…1, pions v 1 (y) at mid-rapidity is plotted measurement from the left panel is re-plotted for comparison. QGSM * model presents the basic Quark-Gluon String model with parton recombination [15]. Hydro * model presents the hydrodynamic expansion from a tiled source [8].…”

Directed Flow of Identified Particles inAu+AuCollisions atSNN=200 GeVat RHIC

“…Following convention, the sign of spectator v 1 in the forward region is chosen to be positive, to which the measured sign of v 1 for particles of interest is only relative. Fitting with a linear function, the slopes are −0.15 ± 0.05(stat) ± 0.08(sys)(%) for the protons, −0.46 ± 0.06(stat) ± 0.04(sys)(%) for the antiprotons, −0.27 ± 0.01(stat) ± 0.01(sys)(%) for the pi- [30]. Hydro* model presents the hydrodynamic expansion from a tilted source [11].…”

“…2, pion and proton v 1 (y) are plotted together with five model calculations, namely, RQMD [12], UrQMD [28], AMPT [29], QGSM with parton recombination [30], and slopes from an ideal hydrodynamic calculation with a tilted source [11]. The model calculations are performed in the same p T acceptance and centrality as the data.…”

Direct photon emission from hadronic sources: hydrodynamics vs. transport theory

“…Some attemps to include multi-particle interactions do exist [14,11,15,16,17], but this field of study is still rather new. The coupling of a partonic phase with a hadronic phase imposes one more problem on transport models.…”