Outline

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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

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QGP in the Laboratory
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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

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Momentum distributions

• 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?

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STAR Detector Subsystems
1st year detectors (2000) 2nd year detectors
3rd year detectors
Coils
TPC Endcap MWPC
Zero Degree Calorimeter
Central Trigger Barrel
RICH
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Physics Run 2000

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

• This analysis
• Tracking TPC
• Trigger ZDC CTB
• PID de/dx in TPC
• TPC
• ? lt 1.8
• 0 lt f lt 2p
• P? gt 75 MeV/c
• Bfield
• 0.25 T (1/2 nominal)
• Trigger
• ZDC at ? 18 m
• CTB ? lt 1

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Identified Spectra dE/dx
Use calibrated curves Z variable
zp ln(Imeas/Ip)
?p
K-
?-
e-
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?- 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
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?- rapidity distribution
Yield fairly flat decreasing slightly with
increasing y y lt 0.1 dN/dy 286 10 y
0.8 dN/dy 271 13
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Teff vs y

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

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?- m? Spectra (centrality)
Range 0.05 lt p lt 0.75 Measure gt80 of total
yield Teff changes slowly with centrality 176
210 MeV
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K- and ?p, m? Distribution
K- Slope moderate centrality dependence Stronger
for ?p
?p dN/dy 20 4
K- dN/dy 43 4
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Inverse Slope Parameters
Slope stronger centrality dependence with
increasing particle mass Radial flow?
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K/h- ratio
Good agreement between dE/dx, Kink and K0s
analyses Kaon yields scale roughly with
multiplicity
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K/p ratio vs. ?s
K/p shows a maximum K-/p- increases
monotonically
Change in rel. contributions of associated vs.
pair production
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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)

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Phase Diagram
e 1-3 GeV/fm3
F. Wilczek hep-ph/0003183

• Heavy Ions How does nuclear matter look at high
  temperature?