Helen Caines Yale University ICPAQGP-Jaipur Nov 2001 STAR 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

Helen Caines ICPAQGP STAR 2 What are we looking for? 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 Baryon / antibaryon ratios Ratios and yields 2 particle correlations Strange baryon ratios Hadron ratios vs. p T m T slopes Anisotropic flow High pt measurements Charged particle mult.,

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

Helen Caines ICPAQGP STAR 4 Event (Centrality) Selection PRL 86, (2001) 402 n ch = primary tracks in |  | < 0.75 ZDC Au Central Multiplicity Detectors 5% Central central collisions  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

Helen Caines ICPAQGP STAR 5 Particle identification Approx. 10% of a central event a) dE/dx b) RICH c) Topology  Kpd e

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

Helen Caines ICPAQGP STAR 7 Particle Multiplicity PRL 87, (2001) Jacobian: h - : 5% most central h - spectra for –1 <  < 1 in accordance with boost-invariant system better: dN/dy from   also flat dN/dy looks boost-invariant BUT change in p T (m T ) slopes for rapidity 0  1 STAR Preliminary Increase in particle production 58% compared to Pb+Pb at √s nn = 17.2 GeV 38% compared to (scaled) pbar+p dN ch /d  = 567±1±38

Helen Caines ICPAQGP STAR 8 Models to Evaluate T ch and  B Assume: Hadron resonance ideal gas Comparable particle ratios to experimental data Q i : 1 for u and d, -1 for  u and  d s i : 1 for s, -1 for  s g i : spin-isospin freedom m i : particle mass T ch : Chemical freeze-out temperature  q : light-quark chemical potential  s : strangeness chemical potential  s : strangeness saturation factor Particle density of each particle: J.Rafelski PLB(1991)333 J.Sollfrank et al. PRC59(1999)1637 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

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

Helen Caines ICPAQGP STAR 10 The flies in the thermal ointment.  /h - = /  /K - =0.084+/ T (MeV) Ratios Braun-Munzinger et al. hep-ph/ Thermal fit results in T ~ 175 MeV Model gets simple ratios correct, but miss multi-strange ratios significantly!!! Statistical errors only +/+/ Preliminary STAR 10% central data  - /K -

Helen Caines ICPAQGP STAR 11 New Point in Phase-Diagram All models so far (despite small differences in the details) give similar results: RHIC  T ch ~ 175 MeV,  B = 50 MeV Compare to QCD on Lattice: T c = 154±8 MeV (N f =3) T c = 173±8 MeV (N f =2) (ref. Karsch QM01) neutron stars Baryonic Potential  B [MeV] early universe Chemical Temperature T ch [MeV] AGS SIS SPS RHIC quark-gluon plasma hadron gas thermal freeze-out deconfinement chiral restauration Lattice QCD atomic nuclei ?! Beam energy dependence  Temperature increases  Baryon chemical potential decreases At RHIC  Fully strangeness equilibration (  s ~1)  Being close to phase boundary

Helen Caines ICPAQGP STAR 12 m T slopes vs. Centrality Increase in slope with collision centrality  consistent with radial flow.

Helen Caines ICPAQGP STAR 13 Mass dependence of m T slopes 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 p T range (dE/dx p < 1 GeV/c) 1/m T dN/dm T (a.u.) m T -m STAR Preliminary

Helen Caines ICPAQGP STAR 14 Hydrodynamics motivated m T fit m T - m 0 (GeV) 1/m T dN/dm T (a.u.) STAR Preliminary R  s E.Schnedermann et al, PRC48 (1993) 2462 Flow profile used  r = s (r/R) 0.5 -- K-K- p  solid : used in fit Shape of the m T spectrum depends on particle mass Inverse-slope depends on m T -range whereand

Helen Caines ICPAQGP STAR 15 K-K- p  -- [c] T th [GeV] [c] T th [GeV] Fits to the hydro. model STAR Preliminary STAR PHENIX T th [GeV] [c] explosive radial expansion at RHIC  high pressure  r (RHIC) = 0.52c T fo (RHIC) = 0.13 GeV

Helen Caines ICPAQGP STAR 16 Comparison of h - and ,  p T dist. STAR Preliminary Suggestive that the ratio baryons/mesons > 1 at high p T Consequence of radial flow ? or novel baryon dynamics ? Vitev and Gyulassy nucl-th/

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

Helen Caines ICPAQGP STAR 18 Low p T v 2 midrapidity : |h| < 1.0 Peripheral  Central First time data is well represented by a hydrodynamical model Mass dependence –Also typical hydrodynamic behavior STAR PRL87 (2001) STAR Model

Helen Caines ICPAQGP STAR 19 M. Gyulassy, I. Vitev, X.N. Wang nucl-th/ v 2 at High p T  STAR Preliminary K p  Flattening at high p T not described by models Appears for identified particles too STAR Preliminary

Helen Caines ICPAQGP STAR 20 Inclusive p T dist. of negative hadrons Preliminary QM01 Hadron suppression by ~ factor 2 at high p T

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

Helen Caines ICPAQGP STAR 22 Summary – First year of STAR 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 Not yet baryon free Unlike ratios similar to SPS High flow creates new picture Models don’t reproduce multi-s Significant radial flow Baryon>meson at high p T Significant increase in multiplicity and mean p T relative to SPS High flow agrees with hydro-dynamics Suppression of particles at high p T Ratios flat as function p T

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

Helen Caines ICPAQGP STAR 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

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

Helen Caines ICPAQGP STAR 26 h - : p T Distributions and  p T  NA49  pp h-h- STAR Preliminary Power Law: A (1+p t /p 0 ) - n h-h- increases with centrality For central collisions higher than in min. bias pp  s = 1.8 TeV (CDF) STAR

Helen Caines ICPAQGP STAR 27 Surprising: source sizes roughly same as at AGS/SPS ( < 10fm) radii increase with centrality (expected for R Out,R Side ) Radii decrease with increasing k T (flow) Unexpected: R Out /R Side ~ 1 The R out /R side Ratio k T = pair p T Rside Rout Hydrodynamical QGP + (URQMD or RQMD) can not reproduce R o < R s STAR data model: R=13.5 fm,  =1.5 fm/c T th =0.11 GeV,  r  = 0.5 c PHENIX Preliminary Consistent T th and  r  with those from spectra and v 2