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Outline

Outline. Background 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 Identified Particle Results Conclusions. QGP in the Laboratory. Global observables.

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Outline

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  1. Outline • Background • 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 • Identified Particle Results • Conclusions

  2. QGP in the Laboratory

  3. Global observables • Inclusive single particle spectra at low p^ • Represent system at Kinetic Freeze-out (Final stage) • Thermalization, Expansion • Boost invariance? • Which particle production mechanisms matter? • Can perhaps help to set constraints • Initial conditions • Evolution of the system • Essential reference for systematic studies of probes of deconfinement

  4. Momentum distributions Factorize? • Difference between SPS and RHIC • At high energy expect • 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?

  5. STAR Detector Subsystems Time Projection Chamber Magnet Silicon Strip Detector Silicon Vertex Tracker Forward Time Projection Chambers Photon Multiplicity Detector Vertex Position Detectors Endcap Calorimeter Barrel EM Calorimeter + TOF patch 1st year detectors (2000) 2nd year detectors3rd year detectors Coils TPC Endcap & MWPC Zero Degree Calorimeter Central Trigger Barrel RICH

  6. Physics Run 2000 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 • Inclusive single particle spectra • Track finding • Corrections: acceptance, efficiency, etc. as a function of • momentum space cell • y-pt • Vertex position • multiplicity • particle species

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

  8. - p & m Spectra (vs. rapidity) Each y bin scaled by factors of 2 Fits to Bose-Einstein Including low-pt No additional low-pt enhancement

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

  10. Teff vs y • Teff shows more pronounced y dependence • Boost invariance does not yet hold at RHIC • Flow? Additional baryons with increasing y?

  11. - m Spectra (centrality) Range 0.05 < p^ < 0.75 Measure >80% of total yield Teffchanges slowly with centrality 176 – 210 MeV

  12. K- andp, m Distribution K- Slope: moderate centrality dependence Stronger for p K- dN/dy = 43 ± 4 p dN/dy = 20 ± 4

  13. Inverse Slope Parameters Slope: stronger centrality dependence with increasing particle mass… Radial flow?

  14. K/h- ratio Good agreement between dE/dx, Kink and K0s analyses Kaon yields scale roughly with multiplicity

  15. K/p ratio vs. s K+/p+ shows a maximum K-/p- increases monotonically Change in rel. contributions of associated vs. pair production

  16. Conclusions • Identified Particle Spectra • visible y dependence: boost invariance not yet reached •  slope parameter Teff, weak centrality dependence • Anti-proton Teff increases dramatically (Radial flow?) • Both K and p yields scale ~linearly with h- • K/ ratio • K+ shows a maximum at s ~ 10, (associated + pair) • K- increases monotonically (pair) • Collision picture including other observables is beginning to emerge (see other STAR talks on HBT, Elliptic Flow v2)

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

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