Eric Vazquez 2012 APS-Division of Nuclear Physics Conference

1. Control study of surface bias emission in 2-particle correlations in Au+Au at √sNN = 200 GeV in PHENIX Eric Vazquez 2012 APS-Division of Nuclear Physics Conference

2. Probing the quark gluon plasma • RHIC: Heavy-ion collisions at √sNN = 200 GeV: • Evidence of strongly interacting colored medium • Strongly interacting medium induces parton energy loss 2012 APS-DNP Fall Meeting

3. Probing the quark gluon plasma • Nuclear modification factor (RAA) was first crude indicator of energy loss. • Compare final state particle production with a “control” system ( scaled proton-proton collisions ) • However, little sensitivity to precise energy loss mechanism 2012 APS-DNP Fall Meeting Significant energy loss

4. Probing the quark gluon plasma • Nuclear modification factor (RAA) was first crude indicator of energy loss. • Compare final state particle production with a “control” system ( scaled proton-proton collisions ) • However, little sensitivity to precise energy loss mechanism • 2-particle correlations provide a probe associated with jets that is sensitive to path length traversed in strongly interacting medium. 2012 APS-DNP Fall Meeting

5. 2-particle correlations at RHIC • Triggering on events with high-pT tracks is an efficient way to probe jet production. “trigger” high-pT track Df 2012 APS-DNP Fall Meeting “associated” lower-pT track

6. 2-particle correlations at RHIC • Triggering on events with high-pT tracks is an efficient way to probe jet production. “trigger” high-pT track Df 2012 APS-DNP Fall Meeting “associated” lower-pT track

7. Jet measurements at RHIC • Both PHENIX and STAR have provided a wealth of measurements providing insight into jet-quenching at RHIC. 2012 APS-DNP Fall Meeting

8. Jet measurements at RHIC • Both PHENIX and STAR have provided a wealth of measurements providing insight into jet-quenching at RHIC. 2012 APS-DNP Fall Meeting Both experiments observe jet-quenching for away-side pairs!!

9. Surface bias emission • However…. • Why is the away-side jet quenched while the near-side jet is not? 2012 APS-DNP Fall Meeting

10. Surface bias emission • However…. • Why is the away-side jet quenched while the near-side jet is not? 2012 APS-DNP Fall Meeting Unmodified pair production Strongly interacting medium

11. Surface bias emission • However…. • Why is the away-side jet quenched while the near-side jet is not? 2012 APS-DNP Fall Meeting Unmodified pair production Modified pair production Strongly interacting medium

12. Surface bias emission • Can we reduce the “surface bias”? • Some proposals to reduce “surface bias” • 2+1 correlations: require two high-pT “triggers" high-pT track Unmodified pair production 2012 APS-DNP Fall Meeting Modified pair production Strongly interacting medium

13. Surface bias emission • Can we reduce the “surface bias”? • Some proposals to reduce “surface bias” • 2+1 correlations: require two high-pT “triggers“ high-pT track Reduction surface bias high-pT track 2012 APS-DNP Fall Meeting Strongly interacting medium

14. Surface bias emission • Can we reduce the “surface bias”? • Some proposals to reduce “surface bias” • 2+1 correlations: require two high-pT “triggers“ • g-h correlations: Colorless probe high-pT track Reduction surface bias high-pT track 2012 APS-DNP Fall Meeting Strongly interacting medium

15. 2+1 di-hadron correlations 2012 APS-DNP Fall Meeting

16. Conditionally triggered events • 2 high-pT track requirement “trigger” high-pT track Df = p 2012 APS-DNP Fall Meeting high-pT track “conditional”

17. Conditionally triggered events • 2 high-pT track requirement • Both high-pT tracks separated in azimuth by: “trigger” high-pT track Df = p Dftc 2012 APS-DNP Fall Meeting high-pT track “conditional”

18. 2+1 correlations pair distribution • Pair distribution is constructed from a high-pT trigger relative to other lower pT fragments “trigger” high-pT track Dfta “associated” tracks 2012 APS-DNP Fall Meeting high-pT track “conditional”

19. 2+1 di-hadron correlations • 2006 p+p at √sNN = 200 GeV 2012 APS-DNP Fall Meeting

20. 2+1 di-hadron correlations • 2007 Au+Au at √sNN = 200 GeV 2012 APS-DNP Fall Meeting

21. Background subtraction • Subtraction is done under the two-source model assumption: • Flow modulated background is modeled by convoluting three single particle flow distributions “background” “correlation” “jet” 2012 APS-DNP Fall Meeting

22. ZYAM procedure • To determine background level, the Zero Yield at Minimum (ZYAM) procedure is employed. 2012 APS-DNP Fall Meeting

23. ZYAM procedure • To determine background level, the Zero Yield at Minimum (ZYAM) procedure is employed. 2012 APS-DNP Fall Meeting

24. Jets: 2+1 di-hadron pair distributions • 2006 p+p at √sNN = 200 GeV 2012 APS-DNP Fall Meeting

25. Jets: 2+1 di-hadron pair distributions • 2007 Au+Au at √sNN = 200 GeV 2012 APS-DNP Fall Meeting

26. Jet yields • Can extract the yield due to jets from 2+1 correlations 2012 APS-DNP Fall Meeting

27. Jet yields • Can extract the yield due to jets from 2+1 correlations Integrate near-side from –p/3 to p/3 2012 APS-DNP Fall Meeting

28. Jet yields • Can extract the yield due to jets from 2+1 correlations Integrate away-side from 2p/3 to p 2012 APS-DNP Fall Meeting

29. Ratio: near-side to away-side • Define ratio: 2012 APS-DNP Fall Meeting

30. Ratio of Integrated Yields(Near-side to Away-side) • Ratio of near-side to away-side integrated yields 2012 APS-DNP Fall Meeting Harder fragments in the direction of higher pT track

31. Ratio of Integrated Yields(Near-side to Away-side) • Ratio of near-side to away-side integrated yields 2012 APS-DNP Fall Meeting

32. Ratio of Integrated Yields(Near-side to Away-side) • Ratio of near-side to away-side integrated yields 2012 APS-DNP Fall Meeting

33. g-h correlations 2012 APS-DNP Fall Meeting

34. The “golden channel” • Photons are “colorless” probes: (i.e. DO NOT interact with strongly interacting colored medium) • Use as photon as calibration for modified away-side jet 2012 APS-DNP Fall Meeting

35. g-h correlations • Comparison of Au+Au to p+p correlations • Extract yields by integrating away-side correlation. 2012 APS-DNP Fall Meeting

36. g-h correlations • Comparison of Au+Au to p+p correlations • Extract yields by integrating away-side correlation. 2012 APS-DNP Fall Meeting

37. Fragmentation yields vs. zT 2012 APS-DNP Fall Meeting Suppression at highzT(low x)

38. Modification significant? • Define different integration regions and compare results. 2012 APS-DNP Fall Meeting

39. Modification significant? • Define different integration regions and compare results. 2012 APS-DNP Fall Meeting

40. Modification significant? • Define different integration regions and compare results. • Suppression significant regardless of integration region!! 2012 APS-DNP Fall Meeting

41. Conclusion • A modification is seen in Au+Au to the topology of the 2+1 correlations. • Harder fragments tend to be biased in the direction of the highest pT track. • Ratio of near-side to away-side yields show significant modification relative to 2006 p+p collision system • Are we reducing surface bias with 2+1 correlation measurement? • Further studies are needed to determine source of modification • Modification is seen in g-h correlations at high zT. 2012 APS-DNP Fall Meeting

42. BACK UP 2012 APS-DNP Fall Meeting

43. 2007 PHENIX detector • Measuring hadrons: • Tracking done via drift chambers and pad chambers • Ring imaging Cerenkov detector allows us to segregate hadrons from electrons below 5 GeV 2012 APS-DNP Fall Meeting

44. Measuring 3 tracks in PHENIX • Remind ourselves that the 2+1 correlation is really a 3-particle measurement. • PHENIX previously published methodology for measuring 2-particle correlations in a limited acceptace detector through event-mixing. • Key point: Can recover physics correlations as long as pair efficiencies can be approximated by single particle efficiencies. 2012 APS-DNP Fall Meeting

45. Measuring 3 tracks in PHENIX • Extend logic to three tracks: • The single particle efficiencies are given by event-mixing which leads to a three event-mixing technique (similar to two event-mixing technique used in 2-particle correlations) 2012 APS-DNP Fall Meeting