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First Results from the STAR Detector at RHIC (Au-Au at  s NN =130 GeV)

First Results from the STAR Detector at RHIC (Au-Au at  s NN =130 GeV). If we knew what we were doing it would not be called research, would it? - A. Einstein. What is the initial environment like for particle production? Energy density Net baryon density Early equilibration

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First Results from the STAR Detector at RHIC (Au-Au at  s NN =130 GeV)

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  1. First Results from the STAR Detector at RHIC(Au-Au at sNN=130 GeV) If we knew what we were doing it would not be called research, would it? - A. Einstein

  2. What is the initial environment like for particle production? Energy density Net baryon density Early equilibration What happens during the initial particle production? Jet production/quenching Chemistry Volume, expansion, emission duration Are re-interactions significant? Rescattering of hadrons Equilibration of strangeness Radial flow What are we looking for? Charged particle mult., <pT> Baryon / antibaryon ratios Anisotropic flow High pt measurements Ratios and yields 2 particle correlations Hadron ratios vs. pT Strange baryon ratios mT slopes

  3. Year 2000, The STAR Detector (Year-by-Year) Time Projection Chamber Silicon Vertex Tracker * FTPCs Endcap Calorimeter Vertex Position Detectors Barrel EM Calorimeter + TOF patch year 2001, year-by-year until 2003, installation in 2003 Magnet Coils TPC Endcap & MWPC ZCal ZCal Central Trigger Barrel RICH * yr.1 SVT ladder

  4. Event (Centrality) Selection 5% Central Data 2000  2.0 M total trigger events taken  844 K central (top 15%)  331 K good (top 5%) central for physics analysis  458 K good min bias events for physics analysis ZDC ZDC Au Au Central Multiplicity Detectors PRL 86, (2001) 402 central collisions  nch = primary tracks in || < 0.75

  5. Particle identification a) dE/dx c) Topology  K p d e b) RICH Approx. 10% of a central event

  6. Anti-Baryon/Baryon Ratios Measured in STAR acceptance Extrapolated yields BRAHMS preliminary STAR data : submitted to PRL BRAHMS data : Quark Matter 2001 central events mid-y averaged over experimental pT Pair product is larger than baryon transport: • Mid-rapidity region not yet baryon-free! • Baryon-pair production increases with s • Weak Centrality dependence of net p 2/3 of protons from pair production 1/3 from initial baryon number transported over 5 units of rapidity

  7. Particle Multiplicity STAR Preliminary STAR Preliminary Jacobian: h- : 5% most central PRL 87, 112303 (2001) dNch /dh= 567±1±38 • h- spectra for –1 < h < 1 in accordance with boost-invariant system • better: dN/dy from   also flat • dN/dy looks boost-invariant BUT • change in pT (mT) slopes for rapidity 0  1 Increase in particle production 58% compared to Pb+Pb at √snn = 17.2 GeV 38% compared to (scaled) pbar+p

  8. Models to Evaluate Tch and B • Statistical Thermal Model • F. Becattini • P. Braun-Munzinger et al. PLB(1999) • Assume: • thermally and chemically equilibrated fireball at hadro-chemical freeze-out • law of mass action is applicable !!! • Recipe: • grand canonical ensemble to describe partition function  density of particles of species i • fixed by constraints: Volume V, , strangeness chemical potentialS,isospin • input: measured particle ratios • output: temperature T and baryo-chemical potential B Chemical Freeze-Out Model J.Rafelski PLB(1991)333 J.Sollfrank et al. PRC59(1999)1637 Assume: Hadron resonance ideal gas Particle density of each particle: Qi : 1 for u and d, -1 for u and d si : 1 for s, -1 for s gi:spin-isospin freedom mi : particle mass Tch : Chemical freeze-out temperature mq : light-quark chemical potential ms : strangeness chemical potential gs : strangeness saturation factor Comparable particle ratios to experimental data

  9. Models to Evaluate Tch and B M. Kaneta, N. Xu P. Braun-Munzinger et al. SQM 2001 Central Chemical freeze-out parameters: Tch = 179±4 MeV, ms= -0.8±2.0 MeV mB = 51±4 MeV, gs= 0.99 ±0.03 Simple pictures seem to work and give similar answers All results preliminary, central and at mid-y

  10. The flies in the thermal ointment. X+/p X-/K- Braun-Munzinger et al.hep-ph/0105229 Thermal fit resultsin T ~ 175 MeV Ratios Preliminary STAR 10% central data Model gets simple ratios correct,but miss multi-strange ratios significantly!!! X/h- = 0.0122+/-0.0006 X/K- =0.084+/-0.006 T (MeV) Statistical errors only

  11. New Point in Phase-Diagram Compare to QCD on Lattice: Tc = 154±8 MeV (Nf=3) Tc = 173±8 MeV (Nf=2) (ref. Karsch QM01) All models so far (despite small differences in the details) give similar results: RHIC  Tch ~ 175 MeV , B = 50 MeV ?! early universe • Beam energy dependence • Temperature increases • Baryon chemical potential decreases • At RHIC • Fully strangeness equilibration (gs~1) • Being close to phase boundary 250 RHIC quark-gluon plasma 200 Lattice QCD Chemical Temperature Tch [MeV] SPS 150 AGS deconfinement chiral restauration thermal freeze-out 100 SIS hadron gas 50 neutron stars atomic nuclei 0 0 200 400 600 800 1000 1200 Baryonic Potential B [MeV]

  12. Increase in slope with collision centrality  consistent with radial flow. mT slopes vs. Centrality

  13. Mass dependence of mT slopes STAR Preliminary Indication of strong radial flow at RHIC Situation appears to be more complicated at RHIC than at the SPS Note: inverse slope depends on the measured pT range (dE/dx p < 1 GeV/c) 1/mT dN/dmT (a.u.) mT-m

  14. Hydrodynamics motivated mT fit p b s  R Shape of the mT spectrum depends on particle mass Inverse-slope depends on mT-range STAR Preliminary solid : used in fit - K- 1/mT dN/dmT (a.u.) where and E.Schnedermann et al, PRC48 (1993) 2462 Flow profile used r =s (r/R)0.5 mT - m0(GeV)

  15. Fits to the hydro. model  p K- Tth[GeV] Tth[GeV] <r> [c] - <r > [c] 0 0.4 <r > [c] Tth [GeV] STAR 0 0.4 PHENIX STAR Preliminary br (RHIC) = 0.52c Tfo (RHIC) = 0.13 GeV explosive radial expansion at RHIC  high pressure

  16. Comparison of h- and L,L pT dist. Suggestive that the ratio baryons/mesons > 1 at high pT Consequence of radial flow ? or novel baryon dynamics ? Vitev and Gyulassy nucl-th/0104066 STAR Preliminary

  17. Event anisotropy z y x • The pressure gradient generates collective motion (aka flow) • Central collisions • radial flow • Peripheral collisions • radial flow and • anisotropic flow Coordinate anisotropy  Momentum anisotropy py Almond shape overlap region in px

  18. Low pT v2 STAR PRL87 (2001)182301 • Mass dependence • Also typical hydrodynamic behavior midrapidity : |h| < 1.0 STAR First time data is well represented by a hydrodynamical model Model Peripheral  Central

  19. v2 at High pT  K p  STAR Preliminary M. Gyulassy, I. Vitev, X.N. Wang nucl-th/0012092 Flattening at high pT not described by models Appears for identified particles too STAR Preliminary

  20. Inclusive pT dist. of negative hadrons Preliminary QM01 Preliminary QM01 Hadron suppression by ~ factor 2 at high pT

  21. pbar/p ratio versus pT pbar/p Preliminary X.N.Wang, Phys. Rev. C 58 (1998) 2321 pbar/p ratio Ratio constant out to 2.5 GeV/c

  22. Summary – First year of STAR Not yet baryon free • What is the initial environment like for particle production? • Net baryon density • Early equilibration • Energy density • What happens during the initial particle production? • Jet quenching • Strangeness production • Volume,expansion, emission duration • Are re-interactions significant? • Rescattering of hadrons • Equilibration of strangeness • Radial flow High flow agrees with hydro-dynamics Significant increase in multiplicity and mean pT relative to SPS Suppression of particles at high pT Models don’t reproduce multi-s High flow creates new picture Ratios flat as function pT Unlike ratios similar to SPS Significant radial flow Baryon>meson at high pT

  23. Outlook – 2001 and Beyond • Additional physics beyond Year 1 July 2001 Already have ~10X statistics of year 2000 Will take some p-p reference data (and of course polarization data) multiply-strange baryons (W)yields & slopes SVT Year 2001 • poidentification, yields, slopes • high pT triggering, transverse energy EMC • measurements of charged hadrons, • strange particles at forward rapidities FTPCs Increased coverage for event-by-event physics Year 2002 Installation of PMD Installation of SSD

  24. The STAR Collaboration Russia: MEPHI - Moscow LPP/LHE JINR - Dubna IHEP - Protvino U.S. Labs: Argonne Berkeley Brookhaven U.S. Universities: Arkansas University UC Berkeley UC Davis UC Los Angeles Carnegie Mellon University Creighton University Indiana University Kent State University Michigan State University City College of New York Ohio State University Penn. State University Purdue University Rice University Texas A&M UT Austin Washington University Wayne State University Yale University Brazil: Universidade de Sao Paolo China: IHEP - Beijing IPP - Wuhan England: University of Birmingham France: IReS Strasbourg SUBATECH - Nantes Germany: MPI – Munich University of Frankfurt India: IOP - Bhubaneswar VECC - Calcutta Panjab University University of Rajasthan Jammu University IIT - Bombay Poland: Warsaw University of Technology

  25. Different views of the same physics ? K p  STAR Preliminary  Evidence of hadron suppression at high pT Sensitive to partonic interaction with matter?

  26. h- : pTDistributions and pT STAR Preliminary h- NA49 pp Power Law: A (1+pt /p0) - n STAR h- <pt> increases with centrality For central collisions higher than in min. bias pp collisions @ s = 1.8 TeV (CDF)

  27. The Rout/Rside Ratio kT = pair pT Rside Rout STAR data Hydrodynamical QGP + (URQMD or RQMD) can not reproduce Ro< Rs PHENIX Preliminary model: R=13.5 fm, t=1.5 fm/c Tth=0.11 GeV, br = 0.5 c • Surprising: source sizes roughly same as at AGS/SPS ( < 10fm) • radii increase with centrality (expected for ROut,RSide) • Radii decrease with increasing kT (flow) • Unexpected: ROut/RSide ~ 1 Consistent Tthandbrwith those from spectra and v2

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