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Understanding Jet Energy Loss with Angular Correlation Studies in PHENIX

Understanding Jet Energy Loss with Angular Correlation Studies in PHENIX. Ali Hanks for the PHENIX Collaboration 24 th Winter Workshop on Nuclear Dynamics South Padre Island, TX April 8th, 2008. Outline. Motivation and some background. Away-side "Mach-cone" effect.

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Understanding Jet Energy Loss with Angular Correlation Studies in PHENIX

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  1. Understanding Jet Energy Loss with Angular Correlation Studies in PHENIX Ali Hanks for the PHENIX Collaboration 24th Winter Workshop on Nuclear Dynamics South Padre Island, TX April 8th, 2008

  2. Outline • Motivation and some background • Away-side "Mach-cone" effect • Near-side "ridge" • Correlations with photons • Conclusions

  3. p+p Au+Au Jet fragmentation in Au+Au • Near-side • jet + ridge (medium response?) • Away-side • Head region (suppressed - jet modification) • Shoulder region (medium response)

  4. pT evolution of correlations Yield enhanced Shoulder structure remains Increase trigger pT Jet reemerges

  5. pT evolution of correlations Increase partner pT Yield enhanced Yield suppressed Jet reemerges

  6. IAA Away-side modification • Modified jet yield vs pT • enhancement at low pT • suppression at high pT • Agrees well with expected jet energy loss and induced gluon radiation • Shoulder is ehanced up to pT~ 4GeV/c

  7. Away-side head vs shoulder • Shoulder enhanced up to pT ≈ 4GeV/c

  8. Away-side peak positions • Fit Method 1: • 2 guassian away-side seperated by D • Fit Method 2: • 3 guassian away-side • one fixed by p+p centered at  • 2 seperated by D Weak pTdependence best explained by mach-cone models

  9. Away-side composition • Shape similar for mesons and baryons • provides constraint on models describing modification of away-side • Baryon to Meson ratio similar to the bulk • incosistent with vacuum fragmentation • consistent with jet induced medium excitation

  10. Near-side  • Broadening in  up to pT ≈ 4GeV/c • Subtracting p+p distribution leaves flat background • consistent with ~flat ridge + unmodified jet

  11. The ridge and shoulder connection • ridge and shoulder pT spectra are softer in Au+Au than in p+p • Shoulder is close to inclusive • ridge may be harder than shoulder • ridge and shoulder balance

  12. IAA Going to high pT • Suppression at high pT agrees with jet energy loss expectations • Widths unmodified within errors • But broadening is predicted

  13. tangential bias surface bias ridge Mach cone trigger partner additional away-side particle Geometric Bias? • -jet • photon non-interacting so no bias effect on trigger • possible associated hadron surface bias at high pT • 2+1 correlations: additional condition of high pT particle on away-side • reduce surface bias • still susceptible to tangential bias intermediate pT high pT Solutions (?):

  14. Leading order (LO) compton annihilation Run 6 p+p @ 200 GeV Per-Trigger Yield (A.U.) 1/Ntrig dN/d(A.U.) pT trigger Run 6 p+p @ 200 GeV -jet correlations in p+p • Photon momentum balances with away-side jet • sensitive to the FF • Statistical subtraction • Technique works over large pT range in p+p • Rγ = N(inclusive γ)/N(decay γ)

  15. Run7 Au+Au 200 GeV CF (A.U.) 7-9 X 3-5 GeV Run7 Au+Au 200 GeV CF (A.U.) 12-15 X 3-5 GeV -jet correlations in Au+Au • Suggests away-side suppresion in Au+Au • sensitive to energy loss of jet inclusive -h

  16. – LHC --RHIC Next to leading order (NLO) Medium induced modifications: Fragmentation photons • Medium induced modifications highly sensitive to energy loss of jets • Direct measurement will improve experimental sensitivity • p+p measurement important test of pQCD

  17. Fragmentation photons • First measurement of it's kind at RHIC • next step measure jet shape properties • ultimately apply procedure to Au+Au Nfrag/Ninc ≈ 0.1 at intermediate pT

  18. Conclusions Modification to two particle correlations seen in Au+Au collisions on both the near and away-side • away-side pT dependence consistent with mach cone scenario while challenging gluon radiation and deflected jet models • modification at intermediate pT suggests dominance of jet induced medium excitations • high pT dominated by jet fragmentation • away-side suppresion consistent with energy loss • unmodified near-side and no observation of broadening in away-side suggests geometric bias • -jet and h- correlations can provide new insight

  19. Backup Slides

  20. 2+1 correlations

  21. IAA Near-side modification • Enhancement at low pT • "Suppression" at high associated pT and low trigger pT • dillusion effect? • Broadening in Df at low trigger and associated pT • Agrees with p+p at high pT

  22. Near side composition

  23. IAA Going to higher pT - the near-side

  24. Ridge cont'd

  25. 0712.3033 nucl-ex Ridge vs Shoulder cont'd Near-side Away-side

  26. Predictions from theory

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