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Jet Quenching A Signature For What?
ET
high energy density (non-equilibrated)
number of potential scattering centers
photons, v2(?)
high energy density (equilibrated)
parton energy loss
J/y
QGP
deconfinement
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Jet Quenching A Signature For What?
ET
high energy density (non-equilibrated)
number of potential scattering centers
photons, v2(?)
high energy density (equilibrated)
parton energy loss
J/y
spectral response of medium to gluons cutoff
for soft gluons in confined matter(?)
QGP
deconfinement
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Hard Probes Light Quark Jets, Charm, Photons

• inclusive transverse momentum spectra
• suppression relative to reference
• chemical composition?
• azimuthal correlations (flow)
• asymmetry in partial quenching
• azimuthal correlations (non-flow)
• jet signatures
• quenching of jets

• charm production
• difference light/heavy?
• direct photons
• first attempts

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Suppression of HadronProduction
J.C. Dunlop et al. , Nucl. Phys. A 698, 515c
(2002)
K. Adcox et al. , Phys. Rev. Lett. 88, 22301
(2002)

• ratio of pT-spectra
• AA central / pp

• RAA 1 for scaling with number of binary
  collisions

• RAA lt 1 for central AuAureactions at RHIC (130
  AGeV)
• observed in neutral pions and charged hadrons
  (PHENIX and STAR)

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Suppression of HadronProduction
M.M. Aggarwal et al., Eur.Phys.J.C 23, 225-236,
2002
K. Adcox et al. , Phys. Rev. Lett. 88, 22301
(2002)

• ratio of pT-spectra
• AA central / pp

• RAA 1 for scaling with number of binary
  collisions

• RAA lt 1 for central AuAureactions at RHIC (130
  AGeV)

• RAA gt 1 for reactions at SPS and ISR

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Energy Dependence of pT-spectra in pp and AA
K. Reygers et al., Hirschegg 2002

• spectra in pp
• strong variationwith beam energy
• flattening of spectra
• power law
• influence of hard scattering

• spectra in AA
• little variation with beam energy
• almost exponential
• influence of thermal production?

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Interlude Thermalization and Hadron Spectra
T.P., nucl-th/ 0207012

• spectra of pions and (anti)protons

• description by hydrodynamical source
• perfect description possible
• Tch 172 2 MeV
• mB 37 4 MeV
• Tkin 123 6 MeV
• lt bT gt 0.45 0.02
• doesnt explain suppression
• need stronger suppression to account for
  additional hydrodynamic production

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Transverse Momentum Spectra
X.N. Wang, Phys. Rev. C 61, 64910 (2000)
K. Adcox, Phys. Rev. Lett. 88, 22301 (2002)

• spectra of neutral pions
• two independent measurements!

• peripheral reactions
• good agreement with expectations from pp

• central reactions
• significant deviations from expectations from pp!

• calculations by X.-N. Wang
• good agreement with jet quenching!
• energy loss 15x higher than incold nuclear
  matter (HERMES)

PHENIX
E. Wang X.N. Wang, hep-ph/0202105
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New Results at 200 GeV

• identified particles are best!
• PHENIX neutral pions at high pT
• identified charged particles to come?
• BRAHMS at higher rapidity

C. Jorgensen, BRAHMS Parallel Saturday
S. Mioduszewski, PHENIX Plenary Monday
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The Reference Spectra in pp

• old reference (UA1) reasonable for pT lt 6 GeV/c
• new measurement of pp in PHENIX
• neutral pions
• same detector, same systematics as AA
• reference for charged hadrons still needed

H. Torii, PHENIX Parallel Saturday
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Neutral Pion Spectra in AuAu at 200GeV
D. dEnterria, PHENIX Parallel Saturday
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Charged Hadron Spectra
C. Jorgensen, BRAHMS Parallel Saturday
200 GeV results from all experiments
J. Jia, PHENIX Parallel Saturday
J. Klay, STAR Parallel Saturday
C. Roland, PHOBOS Parallel Saturday
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Suppression in Hadron Spectra The Nuclear
Modification Factor

• strong suppression in p0
• decreasing with pT
• factor 6 at pT 6-8 GeV/c

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Suppression in Hadron Spectra The Nuclear
Modification Factor

• strong suppression in p0
• decreasing with pT
• factor 6 at pT 6-8 GeV/c
• similar suppression in charged hadrons
• RAA slightly higher at intermediate pT?

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Suppression in Hadron Spectra The Nuclear
Modification Factor

• strong suppression in p0
• decreasing with pT
• factor 6 at pT 6-8 GeV/c
• similar suppression in charged hadrons
• RAA slightly higher at intermediate pT?
• discrepancies in charged RAA between experiments
• Glauber calculations?
• NN-reference?
• better consistency between STAR and PHENIX for
  central/peripheral!

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Charged Spectra Central/Peripheral
J. Jia, PHENIX Parallel Saturday
J. Klay, STAR Parallel Saturday
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High pT Neutral Pion Suppression Comparison To
Theory

• pQCD calculations
• P. Levai, Nucl.Phys.A698 (2002) 631
• X.N. Wang,Phys.Rev.C61 (200) 064910
• I. Vitev, parallel talk, Monday
• time to get quantitative!

S. Mioduszewski, PHENIX Plenary Monday
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Centrality Dependence of Suppression

• RAA for neutral pions as a function of centrality
• gradual decrease
• stronger decrease for higher pT
• no threshold effect
• surface-to-volume?

D. dEnterria, PHENIX Parallel Saturday
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Participant Scaling
P.Steinberg, PHOBOS Parallel Thursday
C. Roland, PHOBOS Parallel Saturday

• Npart scaling observed for total charged
  multiplicity
• not exactly true for limited phase space
• Ncoll term for dN/dh??accidental?
• reasonable approximation for limited centrality
  and pT range
• what about high pT?
• only subtle changes from semi-peripheral to
  central
• most changes in shape happen from pp to
  peripheral AA

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Participant vs. Collision Scaling?
C. Roland, PHOBOS Parallel Saturday
J. Jia, PHENIX Parallel Saturday
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Neutral Pion Suppression as Participant Scaling?

• participant scaling valid in high pT limit?
• participant scaling works better than
  collision scaling
• accidental?
• surface emission?
• does not describe scaling from pp to AA!
• not claimed by PHOBOS

Comparison of central to (semi-)peripheral is
instructive, but Central AA may be seen as
superposition of NN collisions (in independent
collision picture), not as superposition of
peripheral AA
Whos afraid of participant scaling? Relax !
Interesting observation (not trivial at high
pT), but not necessarily physics!
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Centrality Dependence of Spectral Shape

• significant change in spectral shape
• observed in PHENIX and STAR
• mean pT increases at low pT
• mean pT decreases at intermediate pT

J. Jia, PHENIX Parallel Saturday
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Chemical Composition at High pT

• p/p and p/p ratios 1 for pT 3 GeV/c
• p/p ratio decreasing at high pT?

G.J. Kunde, STAR Plenary Monday
T. Sakaguchi, PHENIX Parallel Saturday
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Chemical Composition at High pT

• ratio p/h 0.5 in min.bias
• similar in central reactions
• important baryon and/or kaon contributionout to
  pT 8 GeV/c?

S. Mioduszewski, PHENIX Plenary Monday
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Azimuthal Asymmetries - Elliptic Flow
Adler et al., nucl-ex/0206006

• saturation of v2 observed
• hydrodynamic flow
• increase with pT

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Azimuthal Asymmetries - Elliptic Flow
Adler et al., nucl-ex/0206006

• saturation of v2 observed
• hydrodynamic flow
• increase with pT

• non-equilibrium contribution
• jets (unquenched)
• decrease with pT

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Azimuthal Asymmetries - Elliptic Flow
Adler et al., nucl-ex/0206006

• saturation of v2 observed
• hydrodynamic flow
• increase with pT

• non-equilibrium contribution
• jets (unquenched)
• decrease with pT

• asymmetric energy loss
• increase of v2

• saturation from interplay
• models necessary to disentangle effects

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Elliptic Flow in Minimum Bias AuAu at 200 AGeV

• flow saturates for pT gt 3 GeV/c
• consistent results for STAR and PHENIX
• description with minijet model (D. Molnar)
• v2 at high pT independent of beam energy

STAR preliminary
K. Filimonov, STAR Parallel Saturday
PHENIX preliminary
N.N. Ajitanand, PHENIX Parallel Saturday
STAR preliminary
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Elliptic Flow at Really High Momentum

• STAR charged hadron elliptic flow out to pT 12
  GeV/c !
• finite v2 beyond pT 6 GeV/c for semi-central
• decrease of v2 in central?

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Azimuthal Asymmetries - Non-Flow

• elliptic flow analysis
• flow w.r.t. reaction plane weaker than from
  two-particle-correlations
• non-flow azimuthal correlations
• resonances
• local momentum conservation
• HBT
• jets?
• ...

J. Slivova, CERES Parallel Thursday
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Back-To-Back-Correlations at SPS

• two-photon correlations (from p0)
• strong back-to-backcorrelation in pA
• no jets, but signal of primary collisions
• considerable fraction of available energy
• pC well described by VENUS
• pPb not described
• rescattering?
• need to take into accountin elliptic flow
  analysis in AA!

WA98 pC 158 GeV
S. Bathe, WA98 Parallel Saturday
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2-Jet-Events in pp in the STAR TPC
pp ?dijet from 200 GeV run
D. Hardtke, STAR Plenary Tuesday
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Jet Evidence in Azimuthal Correlations at RHIC

• near-side correlation of charged tracks (STAR)
• trigger particle pT 4-6 GeV/c
• Df distribution for pT gt 2 GeV/c
• signature of jets

• also seen in g (p0) triggered events (PHENIX)
• trigger particle pT gt 2.5 GeV/c
• Df distribution for pT 2-4 GeV/c

M. Chiu, PHENIX Parallel Saturday
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Systematic Study of Jet Correlations at RHIC

• establish near-side (trigger-jet) and far-side
  (counter-jet) correlation in pp
• ansatz correlation in AA as superposition of pp
  signal and elliptic flow
• pp signal from pp data
• elliptic flow from reaction plane analysis
• quantify deviations from pp by integrals around
  Df 0 and Df p
• back-to-back correlation disappears in central
  AuAu

D. Hardtke, STAR Plenary Tuesday
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Counter-Jet Suppression

• jet suppression measure as a function of
  centrality
• trigger-jet
• little modification(?)
• most trigger particles from jets!
• counter-jet
• strong suppression with increasing Npart
• jet quenching?
• inconsistencies for smallertrigger momentum
• to be investigated

D. Hardtke, STAR Plenary Tuesday
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Counter-Jet Suppression

• jet suppression measure as a function of
  centrality
• trigger-jet
• little modification(?)
• most trigger particles from jets!
• counter-jet
• strong suppression with increasing Npart
• jet quenching?
• inconsistencies for smallertrigger momentum
• to be investigated
• centrality dependence similar to quenching of
  neutral pion spectrum!

D. Hardtke, STAR Plenary Tuesday
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Single Electron Spectra

• example electron measurements in PHENIX
• tracking in Drift- and Pad-Chambers
• identification in RICH and EM-calorimeter
• subtraction of background
• photon conversions from mesons and p0-Dalitz
  dominant
• pions measured in the same experiment!
• identification of photonic sources by converter
  method

• yield and spectral shape consistent with PYTHIA
  calculation
• scaling with Ncoll
• little energy loss?

• physics signal?
• main source open charm?

R. Averbeck, PHENIX Parallel Monday
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Photon Measurements at RHIC

• direct photon analysis in PHENIX
• search for thermal photons
• prompt photons as calibration for high pT
  hadron production
• no significant excess over hadron decays observed
• promising results
• important redundancy of PHENIX
• interesting attempt at photons in STAR
• conversion measurement

PHENIX preliminary
PHENIX preliminary
I. Johnson, STAR Parallel Monday
K. Reygers, PHENIX Parallel Monday
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Summary 1

• quenching of high pT hadrons in central reactions
  established
• neutral pions suppressed by 1/6 up to pT 8
  GeV/c
• suppression continuous in centrality (no
  threshold)
• decreasing ltpTgt at high pT for charged hadrons

• chemical compositionnot (yet) jet-like
• only 50 of hadrons are pions
• role of baryons at high pT (p/p, p/p, p/p)?

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Summary 2

• saturation of v2 for pT gt 3 GeV/c
• hydrodynamics important for pT lt 3 GeV/c?
• amount of v2 from partial quenching?
• finite v2 at pT 10 GeV/c?

• jets re-discovered in AA at RHIC
• near-side correlation unmodified
• most trigger particles for pT gt 4GeV/c from
  jets?!

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Summary 3

• jet quenching observed
• counter-jet vanishes in central AA
• centrality dependence similar to pion suppression