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Megan Connors Stony Brook University For the Phenix Collaboration APS Meeting April 13, 2008

Photon-hadron Correlations Measured in Au-Au Collisions at √s NN =200 GeV with the PHENIX Detector. Megan Connors Stony Brook University For the Phenix Collaboration APS Meeting April 13, 2008. Photon tagged jets as probes.

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Megan Connors Stony Brook University For the Phenix Collaboration APS Meeting April 13, 2008

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  1. Photon-hadron Correlations Measured in Au-Au Collisions at √sNN=200 GeV with the PHENIX Detector Megan Connors Stony Brook University For the Phenix Collaboration APS Meeting April 13, 2008

  2. Photon tagged jets as probes • Photons are excellent probes because they do not interact with the strongly coupled medium • RAA≈1 implies no medium effect • γ-h correlations should be sensitive to modified fragmentation function and energy loss γenergy ≈ jet energy M. Connors APS Meeting 4/13/08

  3. Photon Sources π0γγ • Hadron decays • Prompt photons • Compton scattering • Quark anti-quark annihilation • Fragmentation Photons • Final state partons • Jet conversions • Thermal radiation γ γ q q g q g q Compton Annihilation At high pT direct photons dominate! π0suppression Medium Induced M. Connors APS Meeting 4/13/08

  4. ? γ-jets γ q g q M. Connors APS Meeting 4/13/08

  5. PbSc Electromagnetic Calorimeters γ h PbGl γ h γ h What are γ–h correlations? • Trigger on a high pT (>5GeV/c) inclusive photon • Measure Df between photon and all hadrons in the event within a certain pT range • Event mixing corrects for acceptance and combinatorial pairs Event Mixing Δφ M. Connors APS Meeting 4/13/08

  6. Determining the Direct Photon Yield For Singles: Nincl = Ndirect + Ndecay • p0-h decayed via MC to get decay g-h For Pairs: Rg π0 pT [GeV] pT [GeV] M. Connors APS Meeting 4/13/08

  7. γ-h Df Correlation for p+p Run 5 p+p 200 GeV • Inclusive • Decay • Direct γ-h M. Connors APS Meeting 4/13/08

  8. Direct γ-h Df Correlations in Run 6 p+p Subtraction technique works over wide range of pT! Little or no near-side production associated with direct photon triggers pT, photon 1/Ntrig dN/dDf (A.U.) Observe opposing jet contribution in away-side yields Df [rad] pT,hadron M. Connors APS Meeting 4/13/08

  9. Direct γ-h Df Correlations in Run 7 Au+Au • Additional challenges and sources of uncertainty in Au+Au analysis: underlying event subtraction (ZYAM) and elliptic flow subtraction • Working to reduce uncertainties and finish analyzing remaining statistics 7-9 X 2-3 GeV 7-9 X 3-5 GeV Little or no near-side production associated with direct photon triggers 7-9 X 1-2 GeV Away-side yields indicate large jet suppression in g+jet channel 0 M. Connors APS Meeting 4/13/08

  10. Higher pT Inclusive-h • Although the production rate is lower at higher pT, the direct photon signal to background ratio (Rγ) improves. • The accuracy of pQCD calculations also improves at higher pT. Correlation Function(A.U.) Correlation Function(A.U.) Run7 Au+Au 200 GeV Run7 Au+Au 200 GeV 12-15 X 3-5 GeV 7-9 X 3-5 GeV Near/Away-Side > 1 Near/Away-Side ≈ 1 pT, γ M. Connors APS Meeting 4/13/08

  11. Summary • Photon tagged jets are important probes of the medium • Expect photon-hadron correlations to be more sensitive to modified fragmentation function • Run 6 provides baseline measurements for comparisons • Observed suppression of away side jet in early Run 7 AuAu γ-h analysis • Measurements extend over large range of pT M. Connors APS Meeting 4/13/08

  12. Plans • Integrate away-side yields • Run 6 provides baseline measurements for determining fragmentation function • Observe modifications to the fragmentation function from Run 7 AuAu γ-h • Polished results coming soon! X.N. Wang, Z. Huang PRC55 (1997) 3047-3061 γenergy ≈ jet energy M. Connors APS Meeting 4/13/08

  13. Back up Slides

  14. Theoretical Predictions Wang et. al. Phys. Rev. Lett. 77 (1996) 231-234 • Pt spectrum of charged particles from fragmentation in the opposite direction of a photon tagged jet • Ratio of fragmentation functions, IAA, with and without energy loss M. Connors APS Meeting 4/13/08

  15. Constructing the Decay Background To start: Construct g(p0) - h from p0-h Problem is that tagging the p0’s introduces a bias <pT> tagged = <pT> true Developed a pair-by-pair correction procedure Correction Procedure: Per-Trigger Yield from g(p0): Sample MC weight function: • Decay kinematics reproduced by Monte Carlo include energy resolution effects and acceptance (P) • This is just for p0’s, What about contributions from other mesons?  This approach implicitly assumes they have the same associated yield – Analytic Form – w/ Detector Response 15 Quark Matter 2008 Quark Matter 2008 2/8/2008

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