Low energy scan and collective flow at 9 GeV

1. Low energy scan and collective flow at 9 GeV Jiayun Chen , Feng Liu, Shusu Shi, Kejun Wu Weihai , Aug. 9,2009

2. Outline Motivation Collectivity from STAR at 9.2GeV MC Simulation at 9 GeV Summary and Outlook

3. Motivation QM09 : SS Shi (STAR Collaboration) QCD Phase diagram Cross over At RHIC: • pT-NQ scaling • partonic collectivity • deconfinement  RHIC beam energy scan program : ----- Search for critical point. ----- Draw the QCD phase boundary. hot and dense matter with partonic collectivity has been formed at RHIC

4. Motivation Access to large range of mB and T Beam Energy Scan (BES) at RHIC + SPS + FAIR RHIC: advantage of collider mode ! At fixed target geometry: detector acceptance changes with energy track density at mid-y increases fast with energy -> technical difficulties in tracking

5. Collider Acceptance 9.2 GeV √sNN = 9.2 GeV Au+Au Collisions at RHIC √sNN 6 GeV 17 GeV Fix-target Mode NA49 Collider Mode STAR

6. RHIC run 10 (fall 2009) (1) Large energy range accessible (2) Collider geometry (acceptance won’t change with S, track density varies slowly) (3) STAR detectors well suited (large acceptance), tested & understood STAR PAC 2007 Strawman proposal: Note: NA61 @ CERN (starting in 2010): 10, 20, 30, 40, 80, 158 GeV/c

7. STAR experience with Low Energy RHIC running observed apparent rates of collisions surprisingly high (?!) to do: (1) understand background (2) optimize triggering 2001: 19.6 GeV Au+Au 2004: 22.4 GeV Cu+Cu 2007: 9 GeV Au+Au Collectivity from STAR at 9.2GeV STAR TPC image of 9 GeV Au+Au, taken on June 7, 2007 (run 8158119, ev.44), figure from Jeff Langraf

8. STAR Experiment and Collisions at Ecm= 9.2 GeV Collisions recorded in STAR TPC Excellent Particle Identification Analysis based on ~ 3000 good events collected at ~ 0.7 Hz in year 2008 PID will further strengthen with the completion of ToF

9. Azimuthal Anisotropy - Directed Flow QM09 Poster : Jiayun Chen (STAR Collaboration) v1vs.η show different trend between the high and low energy because that the spectator rapidity decreases with incident energy

11. Azimuthal Anisotropy - Elliptic Flow QM08 Lokesh Kumar for STAR With TOF, the pt region will be extended to a higher value. Important to perform the v2 scaling analysis.

12. v1 in AMPT • low energy: • the default AMPT with low-NTMAX consistent with the STAR results. • The melting AMPT seems difficult to describe the data. QM09 Poster : Jiayun Chen

13. MC Simulation at 9 GeV V2 of all Charged Hadrons • About 3231k, 862k, 4370k and 4507k events are used for minibias calculations at UrQMD v2.3 , RQMD v2.4, AMPT v2.1 with string melting and default. • v2 : AMPT with melting > AMPT default > UrQMD >RQMD. Partonic reactions enhance hadrons v2 ! • v2 value at AMPT with melting is about equal to the default at center rapidity, but much larger v2 at high rapidity area – connection to the observed RIDGE: • Early partonic interactions are important!

14. MC vs. Experimental data Only 3k good events for experimental data. Difficult to say which MC model is best suitable.

15. v2 NQ Scaling in AMPT  Crossing and subsequent splitting between meson and baryon at pT~1.2GeV/c Only for AMPT with string melting  like hydrodynamic behavior mass ordering at pT<1.2GeV/c  Obvious hadrons type dependence: NQ Scaling at pT>1.2GeV/c Why is the v2 NQ scaling presented in the AMPT with string melting?

16. Difference for two AMPT versions Zi-Wei Lin,Che Ming Ko,etc., Phys.Rev.C 72,064901(2005), “Multiphase transport model for relativistic heavy ion collisions” Quark coalescence mechanism leads to v2 NCQ scaling

17. Partons Cross Section vs. Hadrons v2 • Default AMPT The breaking of v2 NQ scaling.The partons cross section almost doesn’t affect v2 value. • AMPT with string melting The excellent v2 NQ scaling.Large partons cross section leads to strong v2. The strength of the final hadron v2 is directly related to the partons cross section! • The broken NQ scaling behavior maybe indicates the phase transition from dominant partonic to hadronic matter! wukj@iopp.ccnu.edu.cn

18. v2 in RQMD and UrQMD  The same v2 NQ scaling as AMPT with SM. • (no light quark component) is very important for studying the medium properties. dominant partonic matter dominant hadronic matter v2 from KKbar fusion will not obey the v2 NQ scaling. may be statistical fluctuation? Hadronic interactions -> rough v2NQ scaling The v2 NQ scaling may not be the unique feature of quark coalescence ! wukj@iopp.ccnu.edu.cn

19. Where does v2 NCQ Scaling Come from? elliptic flow: Y.Lu,F.Liu,N.Xu.etc., J. Phys. G: Nucl. Part. Phys. 32 (2006) 1121–1129, denotes the hyper-surface where hadrons are emitted. In the low pt region, frequent rescatterings among hadrons can lead to hydrodynamic-like mass ordering. In the higher pt region(pt>1.5GeV/c), particles early freeze out and lack the hydrodynamics development, and the details of the interaction cross-sections are most important. The hadronic cross sections in UrQMD can been parameterized by AQM. Additive Quark Model cross section only depends on the quark-content of the colliding hadrons K. Goulianos, Phys.Rep.101,169(1983), “Diffractive interactions of hadrons at high energies” Color Strings and ropes -excitation and -fragmentation S.A.Bass, M.Belkacem,etc., Nucl-th/9803035, “Microscopic Models for Ultrarelativistic Heavy Ion Collisions”

20. Summaryand Outlook The unique RHIC energy scan program will map the QCD diagram in sNN =5-50 GeV, (corresponding to μB ~ 600-150 MeV) STAR will measure : yields and particle ratios T vs mB, particle spactra (pt, rapidity, …), strangeness production (K/p, multistrange, …), fluctuations and correlations flow (v1,v2,v4, …) with charged and identified particles, HBT radii, … Search for : - disappearance of partonic activities - onset of critical phenomena: fluctuations, correlations 1) turn on and offsignature of de-confinement (QGP) 2) High statistics is required for v2 in the further experiments.

21. Thank you

23. Azimuthal Anisotropy - Directed Flow QM09 Poster : Jiayun Chen (STAR Collaboration) v1vs.η show different trend between the high and low energy because that the spectator rapidity decreases with incident energy

24. Difference for two AMPT versions Quark coalescence mechanism leads to v2 NCQ scaling

25. Energy scan of v1 at RHIC energy • Centrality dependence: • high energy: clearly dependence • lower energy: seems to be weaker • V1(y) of charged particle from AMPT seems consistent with the RHIC data in sharp • high energy: melting AMPT • low energy: default AMPT • The directed flow wiggle from peripheral to central: • high energy: more clearly transformation • low energy: weak effect by centrality but clearly wiggle • The direction of v1 seems consistent in different energy in mid-rapidity.

26. flow antiflow Motivation Anti-flow/3rd flow component, with QGP  v1 flat at middle rapidity. Directed flow (v1) and phase transition Brachmann, Soff, Dumitru, et. al. , PRC 61 (2000) 024909. L.P. Csernai, D. Roehrich PLB 458, 454 (1999) M.Bleicher and H.Stocker, PLB 526,309(2002)