1. RHIC & AGS Annual User’s Meeting, May 2003 Nu Xu 1 Recent Results from STAR Nu Xu Lawrence Berkeley National Laboratory For the STAR Collaboration

2. RHIC & AGS Annual User’s Meeting, May 2003 Nu Xu 2 P hase diagram of strongly interacting matter CERN-SPS, RHIC, LHC: high temperature, low baryon density AGS, GSI (SIS200): moderate temperature, high baryon density

3. RHIC & AGS Annual User’s Meeting, May 2003 Nu Xu 3 Identify and study the properties of the matter with partonic degree of freedom: - nuclear effects in the intermediate p T region initial conditions parton energy loss due to interaction of dense matter - bulk properties collision dynamics collective motion with the partonic degree of freedom early thermalization (c-quark) Physics goals at RHIC

4. RHIC & AGS Annual User’s Meeting, May 2003 Nu Xu 4Outline 1)Introduction 2) Results from intermediate p T (< 10 GeV/c) -- suppression of particle yields -- ‘jet’ correlations 3) Results of bulk properties -- azimuthal anisotropy -- particle distributions and yields 4) Summary http://www.star.bnl.gov/STAR/

5. RHIC & AGS Annual User’s Meeting, May 2003 Nu Xu 5 Introduction Initial Condition - initial scatterings - baryon transfer - E T production - parton dof System Evolves - parton interaction - parton/hadron expansion Bulk Freeze-out - hadron dof - interactions stop J/  D     K*  K  p  d, HBT v2v2v2v2 TTTT Q2Q2 time partonic scatterings? early thermalization?

6. RHIC & AGS Annual User’s Meeting, May 2003 Nu Xu 6 Key parameters at STAR (i) Spokesperson: John Harris1991 - 2002 Tim Hallman 2002 - now 468 collaborators from 10 countries 49 Institutions 3 U.S. National Laboratories ~ 65 graduate students ~ 60 postdocs Ph.D thesis: ~ 20 (May 2003) Publications:14 PRL / 3 PRC

7. RHIC & AGS Annual User’s Meeting, May 2003 Nu Xu 7 Key parameters at STAR (ii) 1) Magnetic field: 0.5 T 2) Acceptance:   2  charge particle |  |<1.5 dE/dx id. |y|<0.5 V 0 id. |y|< 1.0 charged multiplicity: ~2000 3) dE/dx resolution ~ 8% 4) Momentum resolutions: 1.5% at p T ~ 2 GeV/c 2% at p T ~ 4 GeV/c 5% at p T ~ 10 GeV/c 5) Tracking efficiency > 80% M. Anderson et al., STAR NIM A499, 659(03) Events collected: Au+Au 200 GeV ~ 3 MM.B. 2001 ~ 3 M10%2001 p+p 200 GeV ~13 M2001 d + Au 200 GeV ~ 28 MM.B.2003

8. RHIC & AGS Annual User’s Meeting, May 2003 Nu Xu 8 The STAR detector MagnetCoilsTimeProjectionChamber(TPC)ZCalCentralTriggerBarrel(CTB)RICH Year 2000 Silicon Vertex Tracker (SVT) FTPCEndcapCalFPDBarrel EM Cal (EMCal)TOFpTOFr Year 2001 Year 2003 See talk by Richard Majka, 3:40 pm Friday

9. RHIC & AGS Annual User’s Meeting, May 2003 Nu Xu 9 Particle Identification in STAR Reconstruct particles in full azimuthal acceptance of STAR!

10. RHIC & AGS Annual User’s Meeting, May 2003 Nu Xu 10 Physics at intermediate p T Probes for studying the properties of bulk matter : direct- , DY, and high p T particles – - Spectra and ratios R AA - Statistical  &  Correlations hadrons leading particle suppressed q q ? Gyulassy, Vitev, Wang, and Zhang, nucl-th/0302077

11. RHIC & AGS Annual User’s Meeting, May 2003 Nu Xu 11 Jets from STAR at RHIC Jets from STAR at RHIC (STAR, PRL 90, 082302(2002)) Jets from p + p at 200 GeV ‘Jets’ from Au + Au at 200 GeV

12. RHIC & AGS Annual User’s Meeting, May 2003 Nu Xu 12 Nuclear modification factor R AA 1) R < 1, at low p T  ‘soft’ physics, bulk production, different scaling 2) R = 1 at intermediate p T  no effects 3) R  1 at intermediate p T  nuclear effects Note: N o scaling has been observed up to p T ~ 12 GeV/c in hadron production, from fix target p+A experiment.

13. RHIC & AGS Annual User’s Meeting, May 2003 Nu Xu 13 Suppression at intermediate p T STAR Preliminary Evidence of suppression  early interactions partonic dof ? Cold matter or ‘QGP’ ? Parton-parton interaction or structure function Number of binary collisions: Number of participants: Gyulassy, Wang, et al. nucl-th/0302077 Kharzeev, Levin, McLerran, hep-ph/0210332 STAR measured p+p spectrum used for R AA ! STAR: 200 GeV Au + Au STAR Preliminary

14. RHIC & AGS Annual User’s Meeting, May 2003 Nu Xu 14 Suppression and correlation STAR: 200 GeV Au+Au / p+p Hadron suppression and disappearance of back-to-back ‘jet’ are correlated! STAR PRL 90, 082302 ● Au+Au p + p STAR Preliminary

15. RHIC & AGS Annual User’s Meeting, May 2003 Nu Xu 15 d + Au results (i) STAR Preliminary, May 2003 d+Au R dA is similar to the peripheral results of Au+Au collisions

16. RHIC & AGS Annual User’s Meeting, May 2003 Nu Xu 16 d+Au results (ii) Back-to-back correlations p+p: measured data Au+Au: measured data - B*(1+2v 2 2 cos(2  ) d+Au: measured data - dAu pedestal + pp pedestal STAR Preliminary - d+Au similar to p+p

17. RHIC & AGS Annual User’s Meeting, May 2003 Nu Xu 17 Lesson learned – intermediate p T (1) Spectra at intermediate p T show evidence of suppression and the ratios start to decrease at p T ~ 2 GeV/c (2) Jet-like behavior observed in correlations: - hard scatterings in AA collisions - disappearance of back-to-back correlations Consistent with the final state partonic interactions – “jet quenching”

18. RHIC & AGS Annual User’s Meeting, May 2003 Nu Xu 18 Transverse flow observables As a function of particle mass: Directed flow (v 1 ) – early Elliptic flow (v 2 ) – early Radial flow – integrated over whole evolution Note: 1)Effect of collectivity is accumulative – sum of all processes as long as interactions are there. 2) No thermalization is needed – pressure gradient depends on density gradient and interactions.

19. RHIC & AGS Annual User’s Meeting, May 2003 Nu Xu 19 Anisotropy parameter v 2 y x pypy pxpx coordinate-space-anisotropy  momentum-space-anisotropy Initial/final conditions, dof, EOS

20. RHIC & AGS Annual User’s Meeting, May 2003 Nu Xu 20 STAR: v 2 vs. p T and centrality 1) Saturate at p T > 2.5 GeV/c for all centrality bins 2) There are non-reaction plane related correlations ! It is up to 20% and could be p T dependent! 3) Model comparisons should be careful ! Charged particle v 2 Transverse momentum p T (GeV/c) STAR Preliminary, Au+Au at 200 GeV STAR Preliminary

21. RHIC & AGS Annual User’s Meeting, May 2003 Nu Xu 21 STAR: PID v 2 vs. p T As in 130 GeV collision, the mass dependence of v 2 at low p T (<1 GeV/c) is well described by hydro type calculations – early thermalization at RHIC (?) Filled: Au + Au at 200 GeV Open: Au +Au at 130 GeV Lines: hydro-inspired blast wave fits p K  

22. RHIC & AGS Annual User’s Meeting, May 2003 Nu Xu 22 Strange hadron (K 0,  ) v 2 1) High quality M.B. data! 2) At p t < 2 GeV/c, hydro behavior, v 2 (  ) < v 2 (K) 3) At p t > 2.5 GeV/c, v 2 (  ) > v 2 (K) ! - CGC ? - Coalescence ? - Energy loss ? Partonic dof relevant ? Partonic dof relevant ? Model” P.Huovinen, et al., Phys. Lett. B503, 58 (2001)

23. RHIC & AGS Annual User’s Meeting, May 2003 Nu Xu 23 Coalescence and multi-strange v 2 Coalescence and multi-strange v 2 Coalescence approach seems to work Partonic collectivity at RHIC ? Z. Lin et al., PRL, 89, 202302(02) S. Voloshin, nucl-ex/0210014 R. Fries et al., nucl-th/0301087 D. Molnar et al. nucl-th/0302014 Multi-strange baryon (  ) seems to flow ? STAR preliminary STAR Preliminary

24. RHIC & AGS Annual User’s Meeting, May 2003 Nu Xu 24 Lesson learned – azimuthal anisotropy 1) Charged particle: i) M.B. events, saturated at ~ 15-17%, for p T > 2.5 GeV/c; ii) Non-flow correlations are important, at higher p T region 2) Identified particle: i) p T < 2 GeV/c, M.B. events, hydro calculations fit v 2 (  ) > v 2 (K) > v 2 (p) > v 2 (  ) [ v 2 (heavy) < v 2 (light) ] ii) p T > 2 GeV/c, for all centrality bins, v 2 (  K) v 2 (light) ] 3) Coalescence: i) Seems work in the measured p T region ii) Multi-strange particle v 2 Partonic collectivity ?

25. RHIC & AGS Annual User’s Meeting, May 2003 Nu Xu 25 , K, p spectra from 200 GeV 1)Mid-rapidity transverse momentum distributions, lines are thermal fits. 2)The shape depends on collision centrality and the particle mass. STAR preliminary, |y|<0.1 Au+Au at 200 GeV -- K-K-

26. RHIC & AGS Annual User’s Meeting, May 2003 Nu Xu 26 Bulk rapidity distributions , K, p boost invariant within |y| !

27. RHIC & AGS Annual User’s Meeting, May 2003 Nu Xu 27  transverse momentum spectra 200 GeV: Au + Au collisions: exponential function fits no clear centrality dependence p + p collisions: power-law function fits. STAR Preliminary

28. RHIC & AGS Annual User’s Meeting, May 2003 Nu Xu 28 (a) , K, p mean transverse momentum increase in more central collisions - collective flow; (b)  increases vs. beam energy; (c) and (d) N(  )/N(K) and N(  )/N(h - ) ratios ~ constant vs. collision centrality and beam energy !  K + + K - coalescence inconsistent inconsistent   production sensitive to initial collision (?) to initial collision (?)  systematics vs. centrality and beam energy STAR Preliminary

29. RHIC & AGS Annual User’s Meeting, May 2003 Nu Xu 29  STAR preliminary 200 GeV Au + Au STAR: K 0, , ,  spectra

30. RHIC & AGS Annual User’s Meeting, May 2003 Nu Xu 30 Nuclear modification factor STAR preliminary 1) The p T dependence of R(K 0 ) is different from that of R(  ) 2) At p T ~ 5 GeV/c, R(K 0 ), R(  ), and R(charge) are approaching each other  Flow 0< p T <2 GeV/c ?  Coalescence 2<p T <4 GeV/c ?  Independent fragmentation p T >5 GeV/c ?

31. RHIC & AGS Annual User’s Meeting, May 2003 Nu Xu 31 T fo vs. plane  At given centrality, within this fits, the minimum for  is different from reeze-out earlier than bulk produced ?  At given centrality, within this fits, the minimum for  is different from , K, p. Freeze-out earlier than bulk produced ?  Sensitive to early partonic stage ! (?)  Sensitive to early partonic stage ! (?) STAR Preliminary! 130 GeV Au + Au central collisions

32. RHIC & AGS Annual User’s Meeting, May 2003 Nu Xu 32 STAR: resonance program Au+Au 40% to 80% 1.2  p T  1.4 GeV/c |y|  0.5 STAR Preliminary K *0   *(1520) STAR preliminary p+p at 200 GeV , f 0,  *(892),  ,  *(1385)  *(1520) D 0, D* STAR Preliminary 0.8  p T  0.9 GeV/c |y|  0.5 pp Minimum Bias

33. RHIC & AGS Annual User’s Meeting, May 2003 Nu Xu 33 Resonances mass & width In  and K * results: 1) Width - p T independent 2) Mass - strong p T dependent 3) Evidence of hadronic rescattering and finite duration between T ch and T fo ???Phase-spaceInterference Collision broadening Medium effect STAR preliminary, 200 GeV Au + Au K*K* 

34. RHIC & AGS Annual User’s Meeting, May 2003 Nu Xu 34 Number of events: ~ 20 M STAR preliminary 200 GeV d + Au collisions |y|<1, p T < 4 GeV/c |y|<0.25, 7< p T <10 GeV/c Results from d + Au (iii) Open Charm STAR Preliminary !

35. RHIC & AGS Annual User’s Meeting, May 2003 Nu Xu 35 Bose-Einstein correlations STAR preliminary: 200 GeV Au+Au (  -  - ) & (  +  + ) correlation results 1) Within 0.25 < k T <0.6 GeV/c, no clear k T dependence, why? 2) In coordinate space,  -source at freeze-out ~ initial, why? STAR Preliminary

36. RHIC & AGS Annual User’s Meeting, May 2003 Nu Xu 36 Bose-Einstein correlations y x y x pypy pxpx coordinate-space momentum-space 1) v 2 (p T ) > 0  strong expansion 2) s 2 < 0  not much change in source Self-quenching limit not reach yet.

37. RHIC & AGS Annual User’s Meeting, May 2003 Nu Xu 37 Top 15% Au+Au collisions at 130 GeV Non-statistical 14+0.5% ! Gamma with increased rms Gamma ref. from inclusive p T STAR: Mean p T fluctuations  Strong non-statistical fluctuations  Centrality dependence  PHENIX null result is not inconsistent STAR Preliminary

38. RHIC & AGS Annual User’s Meeting, May 2003 Nu Xu 38 Lesson learned – bulk production and collective motion 1) , K, p (|y| < 0.5): i) and yields indicate large degree of thermalization; ii) Within |y|<0.5, ‘boost invariant’ 2) Multi-strange  (|y| < 0.75): i) Transverse behavior differently from bulk ii) Less sensitive to hadronic interactions Collectivity with partonic dof ? 3) Resonances, correlations, fluctuations: i) Strong p T dependence of the resonances mass ( ,K *0 ): Rescatterings at hadronic stage - Medium effect ? ii) Space-time structure of the freeze-out ‘viewed’ via HBT: Evidence of collective flow iii) Mean p T fluctuation increase compared with reference

39. RHIC & AGS Annual User’s Meeting, May 2003 Nu Xu 39 STAR UPC Program: Interference in Au + Au  Au*Au*  0 Au+Au at 200 GeV 1) Two indistinguishable possibilities: A photon from nucleus 1 scatters from 2 A photon from nucleus 2 scatters from 1 2) Negative parity – destructive inter.   ~ |A 1 - A 2 e ip·b | 2 - At y=0  =  0 [1-cos(p  b)] - p T - For  0 w/ XnXn ~ 20 fm - Clear signal of interference! -   wave function non-local ! - Wave functions contains all amplitudes long after the  decay STAR Preliminary, 200 GeV Au+Au dN/dt (GeV 2 ) -1 Data (w/ fit) No Interference Interference t = p T 2 (GeV 2 ) STAR Preliminary

40. RHIC & AGS Annual User’s Meeting, May 2003 Nu Xu 40 Summary STAR: Study matter under extreme conditions  Bulk properties – partonic collectivity and EOS - azimuthal anisotropy v 2 : elliptic flow - spectra: radial expansion, multi-strange particles - resonances: medium effect and other effects - two-particle correlations: space-time structure  Penetrating probes – intermediate p T - hadron suppression at intermediate p T region < 12 GeV/c R AA depends on particle type at p T < 5 GeV/c - disappearing back-to-back ‘jets’  Strong field QED – UPC program