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

2. 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

3. 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

4. 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

5. 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 %
Secondary/Decay Background 7%
Other contributions
(merging, splitting, etc) less than 2%
~12%
Quark Matter January 2001

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

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

8. 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 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

9. 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 17.2 GeV
30% compared to 200 GeV
Preliminary
Quark Matter January 2001

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

11. h- , Centrality dependence
Quark Matter January 2001

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

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

14. 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

15. -, m Distribution
Quark Matter January 2001

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

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

18. m Inverse Slopes
Quark Matter January 2001

19. Conclusions (Preliminary Results)
Collisions dominated by geometry
Negative hadron distributions (Central collisions)
Increased particle production relative to SPS and UA1
<p> = 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

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

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

22. Corrections For h- Distributions
Magnitudes for Medium  =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

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

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