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Azimuthal Correlation Studies Via Correlation Functions and Cumulants

Azimuthal Correlation Studies Via Correlation Functions and Cumulants

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## 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**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**From ET Distributions**time to thermalize the system (t0 ~ 1 fm/c) eBjorken~ 5 GeV/fm3 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**Reminder - Single Particle Distributions**Au + Au Experiment d + Au Control Experiment Striking difference between d+Au and Au+Au results. Cronin effect dominates in d+Au High-pT Jet Suppression dominate in Au+Au. Final Data Preliminary Data**Significant Jet Yield**Is Purported at RHIC schematic view of jet production leading particle hadrons q q Jets are Sensitive to the QCD medium (dE/dx) hadrons • Jets: • Primarily from gluons at RHIC leading particle Energy loss results in an anisotropy which can serve as an excellent probe of the medium Jets at RHIC Correlation Studies Provide a Complimentary Probe for Possible QGP formation…. (Very Important Signal)**Important Tools for**Correlation Studies • Anisotropy Relative to the Reaction • Cumulants • Correlation Functions**y**Reaction plane Reaction plane method i 2 x Build distribution Relative to Rxn. plane Σ wi*sin(2i) tan(22) = Fourier analyze distribution to obtain anisotropy Σ wi*cos(2i) Measuring Azimuthal Correlations Reaction Plane Method Anisotropy = Flow if non-flow is demonstrably small** Correlations**If Flow predominate Multiparticle correlations can be used to reduce non-flow contributions (N. Borghini et al, PRC. C63 (2001) 054906) Measuring Azimuthal Correlations**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**pT and η dependence of v2**• No apparent dependence of v2 on η over the PHENIX η coverage • Finite v2 at high pT • jets are correlated with low pT particles Reaction Plane ! PHENIX Preliminary PHENIX Preliminary PHENIX Preliminary**Glauber**PHENIX Preliminary y eccentricity x Cumulant Analysis: Centrality Dependence Anisotropy driven by eccentricity : v2 scales with Npart**pT ref**Cumulant Analysis: Dependence on integral pT range • No significant dependence on integral pT of reference PHENIX Preliminary pT**PHENIX Preliminary**Scaling of the anisotropy The differential anisotropy scales with the integral anisotropy**Assorted Two-particle Azimuthal Correlation**Functions Virtues • Asymmetry related to jet properties • Comparison of d+Au and Au+Au can reveal in-medium effects • Flavor dependence can probe details of jet fragmentation • etc**pT**Leading Hadron Assorted Correlations Leading Hadron • Associated particle • Meson • Baryon Correlation Function**pT**PHENIX Setup Azimuthal Correlations Using DC+PC1+PC3+EMC Tracks mesons baryons Baryon & Mesonidentification done using EMC TOF**Assorted Correlation Functions**Associated Mesons PHENIX Preliminary Associated Baryons Noticeable differences in the asymmetries For associated baryons and mesons**associated**associated PHENIX Preliminary associated associated Assorted Correlation Functions • Similar asymmetry trends for associated mesons & baryons in d+Au • Dissimilar trends • for associated mesons and baryons in Au+Au De-convolution of Correlation Function Necessary**De-convolution Ansatz**Fractional yield Harmonic Contribution**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**Typical fit to 3d sim correlation**Good overall representation of the correlation function is obtained**y**Reaction plane i 2 x Simulation Build Correlation Function Relative to Rxn. plane Correlation Perp to Plane Σ wi*sin(2i) tan(22) = Σ wi*cos(2i) Measuring Azimuthal Correlations Relative to the Reaction Plane**Results From Simulations**Correlations Parallel-to-RP Correlations Perpendicular-to-RP Simultaneous Fit Recovers Jet and harmonic properties ~ 10%**PHENIX preliminary**PHENIX preliminary PHENIX preliminary Data Hadron-Hadron correlation (pT(trig)>3GeV/c) See Shinichi’s Talk Flavor composition study in progress -- revealing**High Density partonic material formed Early**leading particle d + Au q q Pressure Gradients Develop in Partonic matter -> elliptic flow -> v2 leading particle Hard Scattered Partons Traverse partonic material Jet-quenching (early) v2 This Scenario has Measurable Consequences Which can be put into Evidence Quantitative estimates Emerging Picture The high energy-density matter responsible for Jet Quenching drives elliptic flow**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. • d+Au: 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