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Energy Dependence of Identified Hadrons Elliptic Flow and QCD Phase Structure

This paper investigates the energy dependence of identified hadrons elliptic flow and its relation to the QCD phase diagram. Results show the scaling behavior of hadrons v2 and the thermodynamic parameters Tch and μb. The paper also discusses the QCD phase diagram and the search for the critical point.

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Energy Dependence of Identified Hadrons Elliptic Flow and QCD Phase Structure

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  1. Energy Dependence of the Identified Hadrons Elliptic Flow and QCD Phase Structure K.J. Wu1,2, F. Liu1,2, and N. Xu1,2,3 1. Institute of Particle Physics, Central China Normal University, Wuhan, 430079, China 2. The Key Laboratory of Quark and Lepton Physics (Huazhong Normal University) Ministry of Education, Wuhan, 430079, China 3. Nuclear Science Division, Lawrence Berkeley National Laboratory, Berkeley, CA94720, USA Outline • Introduction && motivation • Results && discussions - NQ scaling of hadrons v2 - Different v2 between particle and anti-partilce - Thermodynamics parameters Tch && μb • Summary

  2. The QCD Phase Diagram • LGT calculation and models hinted the existence of the critical point on the QCD phase diagram* at finite baryon chemical potential. • - Experimental evidence for either the critical point or 1st order transition *. • *Thermalization has been assumed • M. Stephanov, K. Rajagopal, and E. Shuryak, PRL 81,4816(98); K. Rajagopal, PR D61, 105017 (00) Early universe quark-gluon plasma Cross-over partonic phase hadronic phase RHIC beam energy scan program (BES) : • Locate the critical point. • Draw the QCD phase boundary.

  3. v2 NQ Scaling in High Energy Nucleus Collisions NQ=3 NQ=3 NQ=2 NQ=2 D. Molnar and S. Voloshin, PRL91, 092301 (2003) R. J. Fries et. al., PRC68, 044902 (2003) V. Greco et. al, PRC68, 034904 (2003) X. Dong et.al,Phys.Lett. B597 (2004) 328-332 ...... • The v2 reflects the early collision dynamics.* The v2 of Identified hadrons presents NQ scaling behavior. • The essential degrees of freedom at hadronization seem to be constituent quarks, which have developed a collective flow during the partonic evolution. *J. Adams et al. (STAR Collaboration), Nucl. Phys. A757, 102(2005)

  4. Energy Dependence of v2 NQ Scaling • AMPT model results: • Scaling in v2: partonic dof dominant; • No scaling in v2 : hadronic dof dominant • => • A good tool to search for the phase boundary! • The beam energy dependence of the partonic cross sections will not affect the hadrons v2 NQ scaling behavior. • => • Important for RHIC Beam Energy Scan program. Hadronic Partonic J.Phys.G,37-094029 (2010)

  5. Energy Dependence on v2(pbar)/v2(p) |Y|<0.5 R=1, >27GeV Good v2 scaling Partonic dof dominant R≠1, <9.2GeV Broken v2 scaling Hadronic dof dominant

  6. Particle and Anti-Particle v2 Protons *(-1) • Comparing with experiment, AMPT and UrQMD can reproduce the different v2 in low energies regions, but have opposite signs for protons.

  7. Energy Dependence of Tch &μb Fit function fit to exp. data (0~5%) 0~5% Andronic et al., NPA 834(2010), 237-240c 80~90% • Statistical thermal model (THERMUS) fits π-/π+ K-/K+ pbar/p K-/π- pbar/π- (|Y|<0.1) • Centrality: 0~5% 5~10% 10~20% 20~30% 30~40% 40~50% • 50~60% 60~70% 70~80% 80~90% (Nch in |η|<0.5 as trigger)

  8. Thermodynamic Parameters from AMPT Model Top: 0~5% 80~90% • Higher collision energies, higher Tchand lower μb. • Tch: AMPT partonic > exp. >hadronic. • Strong centrality dependence for Tch& μb. • Tch in partonic AMPT has increase quickly than hadronic AMPT from perpheral to central collisions.

  9. Centrality Dependence • At high energies, Tch & μb decrease gradually from central to perpheral collisions. • At lower energies, due to dominant hadronic interactions, Tch & μbfrom partonic AMPT and hadronic AMPT have small discrepancy.

  10. Partons Cross Section Effect • More partonic interactions can lead to higher Tch & μb.

  11. Summary 1) Hadronic v2 NQ Scaling behavior is a good tool to search for the possible phase boundary. • AMPT models predict: partonic dof dominant: √sNN > 27GeV • hadronic dof dominant: √sNN < 9.2GeV 2) Thermodynamics parameters Tch & μb present strong centrality, partons cross section dependence. • AMPT models predict: • partonic dof dominant: μb< 150 (MeV) • hadronic dof dominant: μb> 270 (MeV) --- Broken hadrons v2 NQ scaling will hint that hadronic dof is dominant. --- Due to the baryon stopping, broken v2 scaling between baryon and anti-baryon will be presented at low collision energies.

  12. Partonic dof dominant Cross over Hadronic dof dominant Phase boundary Critical Point ① ② ③ 27GeV 9.2GeV 0.15 0.27

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