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Recent Results from STAR

Recent Results from STAR. Nu Xu Lawrence Berkeley National Laboratory For the STAR Collaboration. P hase diagram of strongly interacting matter. CERN-SPS, RHIC, LHC: high temperature, low baryon density AGS, GSI (SIS200): moderate temperature, high baryon density.

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Recent Results from STAR

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  1. Recent Results from STAR Nu Xu Lawrence Berkeley National Laboratory For the STAR Collaboration

  2. Phase diagram of strongly interacting matter CERN-SPS, RHIC, LHC: high temperature, low baryon density AGS, GSI (SIS200): moderate temperature, high baryon density

  3. Physics goals at RHIC • Identify and study the properties of the • matter with partonic degree of freedom: • - nuclear effects in the intermediate pT 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)

  4. Outline • Introduction • 2) Results from intermediate pT (< 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. Introduction J/y, D W f X L, K* p, K D, p d, HBT partonic scatterings? early thermalization? Initial Condition - initial scatterings - baryon transfer - ET production - parton dof System Evolves - parton interaction - parton/hadron expansion Bulk Freeze-out - hadron dof - interactions stop Q2 v2 time bT

  6. Key parameters at STAR (i) Spokesperson: John Harris 1991 - 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. Key parameters at STAR (ii) 1) Magnetic field: 0.5 T 2) Acceptance:   2 charge particle ||<1.5 dE/dx id. |y|<0.5 V0 id. |y|< 1.0 charged multiplicity: ~2000 3) dE/dx resolution ~ 8% 4) Momentum resolutions: 1.5% at pT ~ 2 GeV/c 2% at pT ~ 4 GeV/c 5% at pT ~ 10 GeV/c 5) Tracking efficiency > 80% M. Anderson et al., STAR NIM A499, 659(03) Events collected: Au+Au 200 GeV ~ 3 M M.B. 2001 ~ 3 M 10% 2001 p+p 200 GeV ~13 M 2001 d + Au 200 GeV ~ 28 M M.B. 2003

  8. The STAR detector Silicon Vertex Tracker (SVT) FTPC Endcap Cal FPD Barrel EM Cal (EMCal) TOFp TOFr Year 2001 Year 2003 Magnet Coils Time Projection Chamber (TPC) ZCal Central Trigger Barrel (CTB) RICH Year 2000 See talk by Richard Majka, 3:40 pm Friday

  9. Particle Identification in STAR Reconstruct particles in full azimuthal acceptance of STAR!

  10. leading particle suppressed hadrons q q ? Physics at intermediate pT Probes for studying the properties of bulk matter: direct-, DY, and high pT particles – - Spectra and ratios RAA- Statistical  &  Correlations Gyulassy, Vitev, Wang, and Zhang, nucl-th/0302077

  11. ‘Jets’ from Au + Au at 200 GeV Jets from STAR at RHIC(STAR, PRL 90, 082302(2002)) Jets from p + p at 200 GeV

  12. Nuclear modification factor RAA 1) R < 1, at low pT ‘soft’ physics, bulk production, different scaling 2) R = 1 at intermediate pT  no effects 3) R  1 at intermediate pT nuclear effects Note: No scaling has been observed up to pT ~ 12 GeV/c in hadron production, from fix target p+A experiment.

  13. Suppression at intermediate pT STAR: 200 GeV Au + Au 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 Preliminary STAR measured p+p spectrum used for RAA!

  14. Suppression and correlationSTAR: 200 GeV Au+Au / p+p ●Au+Au p + p STAR Preliminary Hadron suppression and disappearance of back-to-back ‘jet’ are correlated! STAR PRL 90, 082302

  15. d + Au results (i) STAR Preliminary, May 2003 d+Au RdA is similar to the peripheral results of Au+Au collisions

  16. d+Au results (ii)Back-to-back correlations • STAR Preliminary • d+Au similar to p+p • p+p: measured data • Au+Au: measured data - B*(1+2v22cos(2) • d+Au: measured data - dAu pedestal + pp pedestal

  17. Lesson learned – intermediate pT (1) Spectra at intermediate pT show evidence of suppression and the ratios start to decrease at pT~ 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. Transverse flow observables • As a function of particle mass: • Directed flow (v1) – early • Elliptic flow (v2) – early • Radial flow – integrated over whole evolution • Note: • 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. coordinate-space-anisotropy  momentum-space-anisotropy y py px x Initial/final conditions, dof, EOS Anisotropy parameter v2

  20. STAR: v2 vs. pT and centrality STAR Preliminary, Au+Au at 200 GeV STAR Preliminary Charged particle v2 Transverse momentum pT (GeV/c) 1) Saturate at pT > 2.5 GeV/c for all centrality bins 2) There are non-reaction plane related correlations ! It is up to 20% and could be pT dependent! 3) Model comparisons should be careful !

  21. STAR: PID v2 vs. pT K Filled:Au + Au at 200 GeV Open: Au +Au at 130 GeV Lines: hydro-inspired blast wave fits p   As in 130 GeV collision, the mass dependence of v2 at low pT (<1 GeV/c) is well described by hydro type calculations – early thermalization at RHIC (?)

  22. Strange hadron (K0 , ) v2 1) High quality M.B. data! 2) At pt < 2 GeV/c, hydro behavior, v2(L) < v2(K) 3) At pt > 2.5 GeV/c, v2(L) > v2(K) ! - CGC ? - Coalescence ? - Energy loss ? Partonic dof relevant ? Model” P.Huovinen, et al., Phys. Lett. B503, 58 (2001)

  23. Coalescence and multi-strange v2 STAR Preliminary 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

  24. Lesson learned – azimuthal anisotropy 1) Charged particle: i) M.B. events, saturated at ~ 15-17%, for pT > 2.5 GeV/c; ii) Non-flow correlations are important, at higher pT region 2) Identified particle: i) pT < 2 GeV/c, M.B. events, hydro calculations fit v2(p) > v2(K) > v2(p) > v2(L)[ v2(heavy) < v2(light) ] ii) pT > 2 GeV/c, for all centrality bins, v2(p, K) < v2(p, L)[ v2(heavy) > v2(light) ] 3) Coalescence: i) Seems work in the measured pT region ii) Multi-strange particle v2 Partonic collectivity ?

  25. , K, p spectra from 200 GeV STAR preliminary, |y|<0.1 Au+Au at 200 GeV - K- • Mid-rapidity transverse momentum distributions, lines are thermal fits. • The shape depends on collision centrality and the particle mass.

  26. Bulk rapidity distributions , K, p boost invariant within |y| < 0.5: for both dN/dy and <pT> !

  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.  systematics vs. centrality and beam energy • (a), K, p mean transverse • momentum <pT> increase • in more central collisions - collective flow; • (b) <pT> 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 •  production sensitive to initial collision (?) STAR Preliminary

  29. STAR: K0, , ,  spectra  STAR preliminary 200 GeV Au + Au

  30. Nuclear modification factor • STAR preliminary • 1) The pT dependence of R(K0) is • different from that of R() • 2) At pT ~ 5 GeV/c, R(K0), R(), • and R(charge) are approaching • each other • Flow 0< pT<2 GeV/c ? • Coalescence 2<pT<4 GeV/c ? • Independent fragmentation pT>5 GeV/c ?

  31. Tfo vs. < bT> plane STAR Preliminary! 130 GeV Au + Au central collisions  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 ! (?)

  32. pp Minimum Bias Au+Au 40% to 80% STAR Preliminary STAR Preliminary 1.2 pT 1.4 GeV/c |y|  0.5 0.8 pT 0.9 GeV/c |y|  0.5 *(1520) STAR preliminary p+p at 200 GeV  K*0 STAR: resonance program , f0, *(892),  , *(1385) *(1520) D0, D*

  33. Resonances mass & width In  and K* results: 1) Width - pT independent 2) Mass - strong pT dependent 3) Evidence of hadronic rescattering and finite duration between Tch and Tfo ??? Phase-space Interference Collision broadening Medium effect  STAR preliminary, 200 GeV Au + Au K*

  34. Results from d + Au (iii)Open Charm STAR Preliminary ! |y|<1, pT < 4 GeV/c |y|<0.25, 7< pT <10 GeV/c Number of events: ~ 20 M STAR preliminary 200 GeV d + Au collisions

  35. Bose-Einstein correlations STAR preliminary: 200 GeV Au+Au (- -) & (+ +) correlation results 1) Within 0.25 < kT <0.6 GeV/c, no clear kT dependence, why? 2) In coordinate space, -source at freeze-out ~ initial, why? STAR Preliminary

  36. py momentum-space y px y x x coordinate-space Bose-Einstein correlations • 1) v2(pT)> 0 strong expansion • 2) s2 < 0  not much change in source • Self-quenching limit not reach yet .

  37. STAR: Mean pT fluctuations Top 15% Au+Au collisions at 130 GeV Non-statistical 14+0.5% ! STAR Preliminary Gamma with increased rms Gamma ref. from inclusive pT • Strong non-statistical fluctuations • Centrality dependence • PHENIX null result is not inconsistent

  38. Lesson learned – bulk production and collective motion 1) , K, p (|y| < 0.5): i) <pT> 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 pT 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 pT fluctuation increase compared with reference

  39. Data (w/ fit) No Interference Interference dN/dt (GeV2)-1 t = pT2 (GeV2) STAR UPC Program: Interference in Au + Au  Au*Au*r0 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. s ~ |A1 - A2eip·b|2 - At y=0 s=s0[1-cos(pb)] - pT <<1/<b> - For r0 w/ XnXn <b> ~ 20 fm • Clear signal of interference! •   wave function non-local ! • Wave functions contains all amplitudes long after the  decay STAR Preliminary STAR Preliminary, 200 GeV Au+Au

  40. Summary STAR: Study matter under extreme conditions • Bulk properties – partonic collectivity and EOS - azimuthal anisotropy v2 : elliptic flow - spectra: radial expansion, multi-strange particles - resonances: medium effect and other effects - two-particle correlations: space-time structure • Penetrating probes – intermediate pT - hadron suppression at intermediate pT region < 12 GeV/c RAA depends on particle type at pT < 5 GeV/c - disappearing back-to-back ‘jets’ • Strong field QED – UPC program

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