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Recent results from the STAR experiment at RHIC

Recent results from the STAR experiment at RHIC. for the STAR collaboration Lawrence Berkeley National Laboratory. Outline. STAR experiment at RHIC Physics results from s NN = 130 GeV Au+Au collisions Very preliminary results from s NN = 200 GeV Au+Au.

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Recent results from the STAR experiment at RHIC

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  1. Recent results from the STAR experimentat RHIC for the STAR collaboration Lawrence Berkeley National Laboratory LBNL

  2. Outline • STAR experiment at RHIC • Physics results from sNN=130 GeV Au+Au collisions • Very preliminary results from sNN=200 GeV Au+Au LBNL

  3. Physics Motivation Kinetic freeze-out Chemical freeze-out hadron parton A A • Goal • Study bulk properties of matter under extremely high energy and particle density • Information of observable come from Parton / hadron level time elastic interaction inelastic interaction space Ultra relativistic heavy ion collision is only the tool to study this issue on the earth LBNL

  4. RHIC BRAHMS PHOBOS PHENIX • Relativistic Heavy Ion Collider at Brookhaven National Laboratory LBNL

  5. STAR Experiment • Solenoidal Tracker At RHIC • ~40 Institutes/Universities • ~300 Collaborators • One of large experiments at RHIC • 2p acceptance in f • Excellent particle Identification LBNL

  6. LBNL

  7. STAR Detector Year 2 Next year or later Time Projection Chamber Magnet Coils Silicon Vertex Tracker TPC Endcap & MWPC yr.1 SVT ladder Silicon Strip Detector FTPCs ZDC ZDC Endcap EMC (half in 2003) Vertex Position Detectors Barrel EMC (install over 4 years) Central Trigger Barrel + TOF patch RICH Year 1 4m LBNL

  8. STAR Event Tracks are reconstructed by online tracking LBNL

  9. Particle Identification p K dE/dx p e |p/Z| [GeV/c] • TOF (year 2) • EMC (year 2) • dE/dx by TPC : p,K,p,d,He,…… • Kink method :K • RICH : 1-3 GeV/c for p/K, 1.5-5 GeV/c for p • Topology : L, X, W, K0s , g • Combinatrics : L, L(1520), K*, f, p0, …… LBNL

  10. Statistics • Year 1 • Minimum bias • w/o vertex cut 0.9M events • Central • w/o vertex cut 0.7M events • Year 2 • Minimum bias • w/ vertex cut 2.6M events • w/o vertex cut 3.4M events • Central • w/ vertex cut 4.7M events • DST production is started as official version LBNL

  11. Publications • Elliptic Flow in Au+Au Collisions at sqrt(snn) = 130 GeV K.H. Ackermann et al. Phys. Rev. Lett. 86 pp. 402-407 (2001). • Midrapidity Antiproton-to-Proton Ratio from Au+Au sqrt(snn) = 130 GeV C. Adler et al. Phys. Rev. Lett. 86 pp. 4778-4782 (2001). • Pion Interferometry of sqrt(snn) = 130 GeV Au+Au collisions at RHIC C. Adler et al. Phys. Rev. Lett. 87 , 082301 (2001). • Multiplicity distribution and spectra of negatively charged hadrons in Au+Au collisions at sqrt(snn) = 130 GeV C. Adler et al. Phys. Rev. Lett. 87, 112303 (2001). • Identified Particle Elliptic Flow in Au+Au Collisions at sqrt(snn) = 130 GeV C. Adler et al. Phys. Rev. Lett. 87, 182301 (2001). • Antideuteron and Antihelium production in Au+Au collisions at sqrt(snn) = 130 GeV C. Adler et al. Phys. Rev. Lett. 87, 262301-1 (2001). • Measurement of inclusive antiprotons from Au+Au collisions at sqrt(snn) = 130 GeV C. Adler et al. Phys. Rev. Lett. 87, 262302-1 (2001). LBNL

  12. Ultra Relativistic Heavy Ion Collision Event anisotropy 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 1) Initial Condition - Baryon number transfer - ET production - partons dof 3) Bulk Freeze-out - hadrons dof - interactions stop 2) System Evolve - parton/hadron expansion time hadronization Particle ratio/yield Momentum distribution Particle correlation (HBT) Coalescence LBNL

  13. Particle Ratio / Chemical Freeze-out • Chemical freeze-out • End of inelastic interactions • Information of number of particle is frozen • The particle ratios are described statistical model • Hadron resonance ideal gas + decay effect • The data are described in SIS over SPS energy (AA), and LEP (e+e-) and SppS (pp) LBNL

  14. Model of Chemical Freeze-out • Hadron resonance ideal gas • density of hadron i is Refs. J.Rafelski PLB(1991)333 J.Sollfrank et al. PRC59(1999)1637 Tch : Chemical freeze-out temperature mq : light-quark chemical potential ms : strangeness chemical potential gs : strangeness saturation factor • Relation to quantum number • Baryon number B = 3q • Strangeness S = q-s All resonances and unstable particles are decayed Comparable particle ratios to experimental data LBNL

  15. Data vs. Model • Chemical freeze-out parameters • Tch = 170±4 MeV • mB =3mq= 40±4 MeV ms = 1.1±2.0 MeV gs = 1.09 ±0.06 c2/dof = 16.7/9 BRAHMS PHENIX PHOBOSSTAR (c2/dof = 12.2/8 w/o X-/h-) LBNL

  16. Phase Diagram Lattice QCD predictions central collisions • Beam energy dependence • Temperature increases • Baryon chemical potential decreases • At RHIC • Being close to phase boundary • Fully strangeness equilibration (gs~1) at central collisions RHIC 130GeV SPS Baryon Chemical Potential mB [GeV] Neutron star parton-hadron phase boundary <E>/<N>~1GeV, J.Cleymans and K.Redlich, PRC60 (1999) 054908 LBNL

  17. pT Distribution / Kinetic Freeze-out s • Kinetic freeze-out • End of elastic interactions • Information of momentum is frozen • Boltzmann distribution + flow effect Blast wave model; E. Schnedermann et al., PRC48(1993)2462 Boosted No Boost LBNL

  18. pT Distribution from STAR L L STAR Preliminary K+ (dE/dx) K- (dE/dx) K- (kink) p K+ (kink) p STAR Preliminary STAR Preliminary 0.4 < pT < 3.6 p- 2 d n - 2 [( ] GeV/c) p X+, X- 2 p dy dp STAR Preliminary pT [GeV/c] T T K0s Central events (top 14%) f p0 0.2 < pT < 2.4 K*0 Statistical error only MT-M0 (GeV/c2) • Inverse slope parameter • Increasing • with centrality • with particle mass LBNL

  19. pT Distribution vs. Centrality ] 2 - GeV/c) [( T dp n dy 2 d T p p 2 <Npart> for p 3457 2899 2214 1529 1024 634 353 202 94 ------- <Npart> for K, p 3457 2809 2358 1809 1358 1004 704 253 STAR Preliminary p- K+ (kink) K+ (dE/dx) K- (kink) K- (dE/dx) p p pT [GeV/c] LBNL

  20. Centrality dependence of T th and <br> ] 2 - GeV/c) [( T dp n dy 2 d T p p 2 p- • Selected similar centrality region in p and K,p • As a function of centrality • Tth ~ 100 MeV • <br> goes up then saturated • Flow profile changed? K+ K- p p 38 115 224 347 <Npart> pT [GeV/c] LBNL

  21. How about Strange Baryons? • Comparison of fit result to L and X • Model has large discrepancy with X data in low pT • X does not have common Tth and br with p,K,p,L STAR preliminary Central data Note: Vertical axis is not same with previous plot LBNL

  22. Mass Dependence of <pT> • Heavy particle is important! ? • X shows a deviation from common thermal freeze-out Kinetic freeze-out model prediction <b>=0 D - KRSX plot - LBNL

  23. Bombarding Energy Dependence <r> [c] Tth [GeV] • From SPS to RHIC • Increasing flow • Decreasing temperature • Longer time for cooling at RHIC? STAR PHENIX LBNL

  24. Summary of Chemical and Kinetic Freeze-out 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 • Chemical Freeze-out • Tch ~ 170MeV, mB ~ 40MeV • Fully strangeness equilibration in central collisions • Kinetic Freeze-out • Tth ~ 100 MeV, br ~0.55c in central collisions • Strong transverse flow • Somehow long time for cooling X data address early freeze-out of multi strangeness baryon! time LBNL

  25. Ultra Relativistic Heavy Ion Collision 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 Particle ratio/yield Event anisotropy 1) Initial Condition - Baryon number transfer - ET production - partons dof 3) Bulk Freeze-out - hadrons dof - interactions stop 2) System Evolve - parton/hadron expansion time hadronization Momentum distribution Particle correlation (HBT) Coalescence LBNL

  26. Event Anisotropy z y x • The pressure gradient generates collective motion (aka flow) • radial flow and anisotropic flow • Hard process may dominant in high pT Almond shape overlap region in coordinate space Momentum space LBNL

  27. v2 vs. Centrality Charged hadron mid-rapidity: |h |<1.0 Hydrodynamic limit STAR: PRL86 (2001) 402 PHOBOS preliminary (PHOBOS : Normalized Paddle Signal) • Central region follows Hydrodynamical model LBNL

  28. Energy Dependence of v2 RQMD(v2.4) • Larger v2 at RHIC than at lower energy collisions min-bias charged hadron STAR Data LBNL

  29. Identified Particle v2  K STAR PRL87, 182301 (2001) p Hydrodynamical model results  STAR preliminary 0.2 Event anisotropy v2 J. Fu, LBNL P. Sorenson, UCLA Event anisotropy v2 0.1 STAR Preliminary 0 2 3 1 0 pT [GeV/c] pT [GeV/c] • Particle mass dependence • Typical Hydrodynamical type behavior • Deviation in high pT region Hydrodynamical prediction LBNL

  30. v2 vs. pT STAR preliminary K. Filimonov, LBNL STAR preliminary • Au+Au at 130 GeV • At pt >2 GeV/c, • v2 saturates; • 2) The saturation values increases with impact parameters; 3) Clearly different from hydrodynamical model (simply increasing with pT and no saturation) predictions. LBNL

  31. Particle Correlation Hanbury-Brown Twiss correlation • Probe of the space time extent of heavy ion collisions • Radius parameters • space-time geometry of the emitting source • dynamical information (e.g. collective flow) LBNL

  32. Radius Parameters pp correlation • Similar radius with SPS! • Strong space-momentum correlation? Kt = pair Pt Rside Rout STAR data : PRL87(2001) 082301 LBNL

  33. Radii vs. pT STAR PRL87(2001) 082301 Blast wave model : Mike Lisa, ACS Chicago, 2001 p+p+ p-p- model: R=13.5 fm, t=1.5 fm/c Tth=0.11 GeV, br = 0.5 c pT [GeV/c] PHENIX: nucl-ex 0201008 • Blast wave model describes pT dependence • Consistent Tthand br with them from spectra and v2 line: kT dependence of transverse flow • However…… • PHENIX data shows Ro/Rs is a constant LBNL

  34. Coalescence d p n • Production through final-state coalescence of antinucleons: • BA • Small systems: • Sensitive to size of produced (anti)nucleus • Large systems: • Sensitive to geometry of system • Antinucleus production • Direct pair production negligible • No background where p = momentum / A LBNL

  35. Beam Energy Dependence of B2 and B3 d (0.5<pT<0.8 GeV/c, |y|<0.3) ~50 times (SPS) ~6×104 times (AGS) No Dramatic Increase in Volume! 3He (1.0<pT<5.0 GeV/c, |y|<0.8) LBNL

  36. Coalescence Geometry Thermal Coalescence Model Thermal and chemical equilibrium of coalescence source Hydro motivated density matrix formulation of coalescence Calculate “homogeneity volume” aka HBT Model: A. Z. Mekjian, PRC 17, 1051 (1978) S. Das Gupta and A. Z. Mekjian, Phys. Rep. 72, 131 (1981). Model: R. Scheibl and U. Heinz, Phys. Rev. C 59, 1585 (1999). Model: H. Sato and K. Yazaki, PL 98B, 153 (1981). LBNL

  37. Summary 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 核子 • Chemical Freeze-out • Tch ~ 170MeV, mB ~ 40MeV • Fully strangeness equilibration • Kinetic Freeze-out • Tth ~ 100 MeV br ~0.55c • Strong transverse flow • long time for cooling? • Event anisotropy • Strong anisotropic flow effect at RHIC! • Saturation of v2 at high pT • Hydrodynamical picture works at low pT • Particle correlation (HBT) • Strong space-momentum correlation • No perfect model to describe the data • Antinucleus / Coalescence • Large enhancement in yield over lower energies • No large volume increase over SPS • 3He freeze out from smaller volume than d time LBNL

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