Outline Background Global Observables in Heavy Ion Collisions Quark-Gluon Plasma and Heavy Ions Global Observables in Heavy Ion Collisions What are they? What do we learn from them? The STAR Experiment Analysis of Charged Particles in STAR Results Charged hadrons: h- Identified particles Conclusions January 7, 2002

Phase Diagram e ~ 1-3 GeV/fm3 F. Wilczek hep-ph/0003183 Heavy Ions: How does nuclear matter look at high temperature? January 7, 2002

QGP in the Laboratory Space-time evolution of HI collision January 7, 2002

Global observables First tool to probe the collision environment Multiplicity distribution Inclusive single particle spectra at low p^ Represent system at Kinetic Freeze-out Thermalization, Expansion Boost invariance? Initial conditions & Evolution of the system Essential reference for systematic studies of probes of deconfinement January 7, 2002

Glauber Model: TAA, Npart, Ncoll Collision Geometry Use Woods-Saxon density profile: from e-A Overlap Integral: s: Binary Collisions: Participants: January 7, 2002

Charged particle production How many particles? Multiplicity distribution Geometry of the collision Correlated with impact parameter January 7, 2002

Momentum distributions Difference between SPS and RHIC At high energy larger contribution from jets, mini-jets h- p^ distribution closer to power law than exponential y distribution  plateau at mid-rapidity spectra peaked at low energy (“stopping”), boost invariance at RHIC? Factorize? January 7, 2002

Predictions (s = 200 GeV) Different models  different predictions pQCD parton models : Hijing dNch/dh = 550 - 800 EKS dNch/dh = 1000 - 1200 Parton hard scattering : Nexus dNch/dy ~ 1100 Microscopic Transport : UrQMD dNch/dy ~ 900 Different models  different predictions Within any model, data needed as initial conditions January 7, 2002

The STAR Detector at RHIC January 7, 2002

Time evolution of STAR 1st year detectors (2000) 2nd year detectors 3rd year detectors Magnet Time Projection Chamber Coils Barrel EM Calorimeter Endcap Calorimeter Silicon Strip Detector Photon Multiplicity Detector Silicon Vertex Tracker Forward Time Projection Chambers Vertex Position Detectors + TOF patch TPC Endcap & MWPC Zero Degree Calorimeter Central Trigger Barrel RICH January 7, 2002

Au+Au in STAR TPC High Multiplicity Event  End view of detector Side View  January 7, 2002

Physics Run 2000 zvertex Multiplicity distribution Event selection, triggers, vertex finding efficiency Inclusive single particle spectra Track finding Corrections: acceptance, efficiency, etc. as a function of momentum space cell h-pt, h- y-pt, p- zvertex multiplicity particle species This analysis: Tracking: TPC Trigger ZDC + CTB PID: de/dx in TPC TPC: || < 1.8 0 < f < 2p P > 75 MeV/c Bfield: 0.25 T (1/2 nominal) Trigger: ZDC at  18 m CTB || < 1 January 7, 2002

Event Selection and Triggers Zero Deg. Cal. Main Minimum Bias Trigger 99% Efficient even at high multiplicity Trigger ZDC Coincidence (East and West) OR High CTB Signal Au Au ZDC East ZDC West Central Trigger Barrel (CTB) 5% Central January 7, 2002

Primary h- Multiplicity 6% sys. error shown on 3 points only January 7, 2002

h- & h+ dN/dh, Central Events Jacobian dN/dh, |h|<0.1 h- : 280 1 20 h+ : 287 1 20 Approaching boost invariance at RHIC January 7, 2002

h- p Distribution, Central Power Law Fit (p^ = 0.2 - 2 GeV/c) A (1+p  /p0) - n p0 =3.0 ± 0.3 GeV/c n= 14.8 ± 1.2 STAR <p>=0.508 ± 0.012 GeV/c NA49 <p>=0.414 ± 0.004 GeV/c UA1 <p>=0.392 ±0.003 GeV/c January 7, 2002

p Spectra in pp Collisions Data available for s = 20-1800, but not at 130 GeV Power law: E d3/d3p = A (1+p^/p0) –n interpolate A, p0, n to 130 GeV Extrapolation used in STAR January 7, 2002

Comparison topp Low pt  Wounded Nucleon applies Compare to UA1 Problem UA1 s = 200 R(130/200) From power law scaling R = 0.92 at 0.2 GeV/c R = 0.70 at 2 GeV/c “Hard” Scaling Nuclear Overlap Integral TAA = 26 mb-1 for 5% most central NAA/Npp= Nbin coll=1050 “Soft” Scaling NAA / Npp=( 344/ 2 ) Low pt  Wounded Nucleon applies Rising pt  Approaching hard scaling limit? January 7, 2002

High p Analysis Preliminary High-pt analysis shows turnover Quenching? January 7, 2002

h- Centrality Classes Central collisions: cut on ZDC only (CTB veto on low multiplicity) Peripheral collisions: Cut in ZDC+CTB space STAR January 7, 2002

h- , Centrality dependence Power Law behavior is observed in all centrality classes, although curvature varies. STAR Shape of dN/dh at mid-rapidity does not change with centrality. Power Law A (1+p  /p0) - n January 7, 2002

h- <p>, Centrality Dependence 15% Increase in <p> from 80% sample to 5% central Increase with respect to pp Collective effects Systematic uncertainty shown for STAR data January 7, 2002

- m Spectra (centrality, y) Fits to Bose-Einstein Including low-pt No additional low-pt enhancement January 7, 2002

K- and p, m Distribution K- Slope: moderate centrality dependence Stronger for p January 7, 2002

m Inverse Slopes Slope: stronger centrality dependence with increasing particle mass Radial flow? January 7, 2002

- rapidity distribution Yield fairly flat decreasing slightly with increasing y |y| < 0.1 dN/dy = 286 ± 10 y= ± 0.8 dN/dy = 271 ± 13 January 7, 2002

Teff vs y Teff shows more pronounced y dependence Boost invariance does not yet hold at RHIC Flow? Additional baryons with increasing y? January 7, 2002

Conclusions Collisions dominated by geometry Negative hadron distributions (Central collisions) Increased particle production relative to SPS and UA1 <p> = 0.508 GeV/c (NA49 = 0.414, UA1 = 0.392) low p: ‘Wounded nucleon’ scaling; rising p: ‘binary collisions’ scaling ? Negative hadrons, centrality dependence <p> shows weak dependence  dependence ~flat, small dependence on centrality Identified  slope parameter T, weak centrality dependence Increase is most dramatic in anti-protons (Radial flow) visible y dependence: boost invariance not yet reached Collision picture including other observables is beginning to emerge January 7, 2002

Identified Spectra: dE/dx Use calibrated curves: Z variable zp = ln(Imeas/Ip) p K- - e- January 7, 2002

- p^ distribution, centrality Fits to Bose-Einstein Including low-pt No additional low-pt enhancement 0.05 < p^ < 0.75 Measure >80% of total yield Teff almost constant with centrality January 7, 2002

- Teff, centrality dependence Slight increase in Teff with centrality Mainly in peripheral From 3d bin, consistent with no centrality dependence Even with radial flow, p are only slightly affected, small m January 7, 2002

- p^ distribution, rapidity 5% Most Central Mid-rapidity region range |y|<0.8  Fits to Bose-Einstein No low-p^ enhancement Each y bin scaled by factors of 2 January 7, 2002

PID & dE/dx Resolution p - e- K- dN/dZp Resolution ~9% 0.4 < p <0.45 GeV/c |y| < 0.1 Resolution ~9% Approaching design value of 8 % January 7, 2002