Azimuthal Correlation Studies Via Correlation Functions and Cumulants

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Azimuthal Correlation Studies Via Correlation
Functions and Cumulants
N. N. Ajitanand Nuclear Chemistry, SUNY, Stony
Brook
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Outline

• Motivation
• Why Correlation studies ?
• Correlation Techniques
• Cumulant Method
• Correlation Function Method
• Correlation Results
• Compatibility with Flow, Jets, etc. ?
• What the Measurements tell us
• Summary

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Why Study Correlations at RHIC
BRAHMS rapidity distribution
Substantial Energy Density is Produced at RHIC
Large Energy Density Substantial
Flow (Hydro limit) Possible Access to EOS
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Reminder - Single Particle Distributions
Au Au Experiment
d Au Control Experiment
Preliminary Data
Final Data

• Striking difference between dAu and AuAu
  results.
• Cronin effect dominates in dAu
• High-pT Jet Suppression dominate in AuAu.

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Jets at RHIC
Correlation Studies Provide a Complimentary Probe
for Possible QGP formation. (Very Important
Signal)
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Important Tools for Correlation Studies

• Anisotropy Relative to the Reaction
• Cumulants
• Correlation Functions

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Measuring Azimuthal Correlations
Reaction Plane Method
Anisotropy Flow if non-flow is demonstrably
small
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Measuring Azimuthal Correlations
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Application of Cumulant Method in PHENIX

• Cumulant analysis non-trivial PHENIX analysis
• Simulations performed using a toy model MC
  generator with PHENIX acceptance as input
• Results show that the
• v2 extracted is robust and
• acceptance corrections are
• well implemented

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pT and ? dependence of v2
PHENIX Preliminary
PHENIX Preliminary
PHENIX Preliminary

• No apparent dependence of v2 on ? over the
  PHENIX ? coverage
• Finite v2 at high pT
• jets are correlated with low pT particles
• 
  Reaction Plane !

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Cumulant Analysis Centrality Dependence

• Anisotropy driven by eccentricity v2 scales
  with Npart

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Cumulant Analysis Dependence on integral pT range
PHENIX Preliminary
pT

• No significant dependence on integral pT of
  reference

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Scaling of the anisotropy

• The differential anisotropy scales with the
  integral anisotropy

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Assorted Two-particle Azimuthal
Correlation Functions
Virtues

• Asymmetry related to jet properties
• Comparison of dAu and AuAu can reveal
  in-medium effects
• Flavor dependence can probe details of jet
  fragmentation
• etc

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Leading Hadron Assorted Correlations
Leading Hadron

• Associated particle
• Meson
• Baryon

Correlation Function
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PHENIX Setup
Azimuthal Correlations Using DCPC1PC3EMC
Tracks
mesons
baryons
Baryon Meson identification done using EMC TOF
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Assorted Correlation Functions
Associated Mesons
PHENIX Preliminary
Associated Baryons
Noticeable differences in the asymmetries For
associated baryons and mesons
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Assorted Correlation Functions

• Similar asymmetry trends for associated mesons
  baryons in dAu

• Dissimilar trends
• for associated mesons and baryons in AuAu

De-convolution of Correlation Function Necessary
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De-convolution Ansatz

Harmonic Contribution
Fractional yield
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Test of de-convolution via Simulations
Two source 3d simulation Simulation Model

• jets and flow.
• Poisson sampling
• jets per event
• particles per jet
• flowing particles per event
• Jets produced with effective jT and kT
• Avg. number of near and far-side jet particles
  equal
• Exponential pT distribution for particles

Correlation functions generated in PHENIX
acceptance
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Typical fit to 3d sim correlation
Good overall representation of the correlation
function is obtained
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Measuring Azimuthal Correlations
Relative to the Reaction Plane
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Results From Simulations
Correlations Parallel-to-RP
Correlations Perpendicular-to-RP
Simultaneous Fit Recovers Jet and harmonic
properties 10
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Reliable yield extraction is achieved
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Data Hadron-Hadron correlation (pT(trig)gt3GeV/c)
See Shinichis Talk
Flavor composition study in progress -- revealing
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Emerging Picture
The high energy-density matter responsible for
Jet Quenching drives elliptic flow
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Summary / Conclusion

• Differential azimuthal anisotropy has been
  measured in PHENIX
• using cumulants.
• 2nd order v2 measured as a function of pT and
  centrality
• Scaling behavior demonstrated
• Low and high pT reference study suggest that
  jets are correlated with RP
• Assorted Correlation Functions
• Azimuthal Correlation functions obtained fro
  high pT leading hadrons in association with
  flavor identified partners.
• dAu significant asymmetry observed for both
  flavors
• Au Au Asymmetry significantly reduced for
  associated baryons
• De-convolution method for extraction of jet and
  flow parameters demonstrated