STAR Geometry and Detectors Event selection and triggers Analysis and Corrections to raw data Negative Hadron, - , K- andp Spectra Conclusions

Charged Hadrons Global observable: event characterization Represent system at kinetic freeze-out Constrains conditions on initial phase of the collision Supply information on evolution of system Study features of collisions at RHIC energy Comparison with pp at similar energy (UA1) Comparison with A+A at lower energies (SPS) Quark Matter January 2001

STAR Geometry This analysis: 86 K min. bias events This analysis: ZDC Barrel EM Calorimeter Endcap Calorimeter Magnet Coils TPC Endcap & MWPC FTPCs Vertex Position Detectors Central Trigger Barrel Time Projection Chamber Silicon Vertex Tracker RICH 2 m 4 m 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 This analysis: 86 K min. bias events Quark Matter January 2001

Event Selections and Triggers ZDC Main Minimum Bias Trigger 99% Efficient even at high multiplicity Trigger ZDC Coincidence (East and West) OR High CTB Signal 5% Central Quark Matter January 2001

Analysis and Corrections For h- Distributions TPC Tracks Corrections: embedding simulated tracks in real events Large acceptance ~95% at mid-rapidity over full azimuth Important correction factors From Tracking efficiency 8-15% Secondary/Decay Background 7% Other contributions (merging, splitting, etc) less than 2% ~12% Quark Matter January 2001

Primary h- Multiplicity Preliminary 6% sys. error shown on 3 points only Quark Matter January 2001

h- p Distribution Preliminary Power Law A (1+p  /p0) - n STAR p0 =2.74 ± 0.11 GeV/c n= 13.65 ± 0.42 STAR <p>=0.514 ± 0.012 GeV/c NA49 <p>=0.414 ± 0.004 GeV/c UA1 <p>=0.392 ±0.003 GeV/c Preliminary Quark Matter January 2001

Comparison topp Preliminary Compare to UA1 Problem UA1 s = 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 ) Preliminary Low pt  Wounded Nucleon applies Rising pt  Approaching hard scaling limit? Reach it? Quark Matter January 2001

h-  Distribution Preliminary Assuming 344 participants in 5% most central collisions: (dN/dh)/(Npart/2) = 1.53  0.13 dN/dh = 244  1  16 (p > 100 MeV/c) dN/dh = 264  1  18 (Extrapolation to all p) Increased particle production: 43% compared to Pb+Pb @ 17.2 GeV 30% compared to pp @ 200 GeV Preliminary Quark Matter January 2001

Centrality Classes Central collisions: cut on ZDC only Peripheral collisions: Cut in ZDC+CTB space STAR Preliminary Quark Matter January 2001

h- , Centrality dependence Quark Matter January 2001

h- p, Centrality Dependence STAR Preliminary Power Law A (1+p  /p0) - n Quark Matter January 2001

h- <p>, Centrality Dependence NA49 UA1 15% Increase in <p> from 80% sample to 5% central Systematic errors shown Quark Matter January 2001

dE/dx Particle Id p p dN/dZp - K d e-  K- e 0.4 < p <0.45 GeV/c |y| < 0.1 - K p d e-  K- p e Use calibrated curves: Z variable Zp = ln(Imeas/Ip) Quark Matter January 2001

-, m Distribution Quark Matter January 2001

K-, m Distribution For the most central bin: T ~ 300  15 MeV. Syst. error ~30 MeV Slope: moderate centrality dependence Quark Matter January 2001

p, m Distribution Slope: stronger centrality dependence Peripheral ~200 MeV Central ~550 MeV. Syst. error on T ~ 50 MeV. Quark Matter January 2001

m Inverse Slopes Quark Matter January 2001

Conclusions (Preliminary Results) Collisions dominated by geometry Negative hadron distributions (Central collisions) Increased particle production relative to SPS and UA1 <p> = 0.516 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 eta dependence ~flat, small dependence on centrality Identified pi, K, p slope parameter T increase with centrality Increase is most dramatic in anti-protons Radial flow? Quark Matter January 2001

TPC Performance All hits and tracks: - red = low pT - violet = high pT Hit Position residuals cosmic data ~ 500 mm Quark Matter January 2001

Reconstruction Efficiency Monte Carlo tracks embedded into real events. Shown: -Med. Multiplicity - |  | < 0.1 N Found / N Accepted Quark Matter January 2001

Corrections For h- Distributions Magnitudes for Medium Multiplicity @  =0 Efficiency ~88%, p> 0.2 GeV/c Acceptance ~95%, p> 0.4 GeV/c Decay/secondary Backgrounds ~7%, p> 0.6 GeV/c Electron background <2%, p> 0.4 GeV/c Resolution <2 %, p >0.1 Merging (<1%) Splitting (<½ %) Ghost Tracks less ~ 1 ‰ Quark Matter January 2001

Simulated tracks Embedded into Momentum Resolution Simulated tracks Embedded into Real events Resolution from Cosmic Data Quark Matter January 2001

PID & dE/dx Resolution Resolution approaching ~8% (Design) Quark Matter January 2001