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Studying the Medium Response by Two Particle Correlations

Studying the Medium Response by Two Particle Correlations. John Chin-Hao Chen (for PHENIX Collaboration) Department of Physics and Astronomy Stony Brook University RHIC & AGS Annual Users' Meeting 05/27/2008. Outline. Why do we use two particle correlations?

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Studying the Medium Response by Two Particle Correlations

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  1. Studying the Medium Response by Two Particle Correlations John Chin-Hao Chen (for PHENIX Collaboration) Department of Physics and Astronomy Stony Brook University RHIC & AGS Annual Users' Meeting 05/27/2008 RHIC & AGS User Meeting

  2. Outline • Why do we use two particle correlations? • What do we learn from two particle Df correlations? • What do we learn from two particle Dh-Df correlations? RHIC & AGS User Meeting

  3. Is there a jet? • In heavy ion collisions, due to huge background of soft particles, it is difficult to find the jet. • So we turn to two particle correlations RHIC & AGS User Meeting

  4. What is two particle correlation? • We select a high pT particle as the trigger particle. • Select another lower pT particle, calculate the angular Df distribution. • Use ZYAM (Zero Yield At Minimum) method to remove the flow background. RHIC & AGS User Meeting

  5. The jet has disappeared! • In p+p and d+Au collisions, we see a clear awayside peak • In central Au+Au collision, the awayside peak is disappeared. Phys. Rev. Lett. 91, 072304 RHIC & AGS User Meeting

  6. The jet is modified! The awayside peak moved to ~ p +/- 1.1 in central collisions! Phys. Rev. Lett. 98, 232302 (2007) RHIC & AGS User Meeting

  7. The nearside is also modified! • The nearside width is wider than pp • The yield at low partner pT is also larger than pp   arXiv:0801.4545 RHIC & AGS User Meeting

  8. 2-D Dh-Df correlations Peripheral Au+Au Central Au+Au Dh Dh shoulderridge Df Df rad Both near and away side are modified! RHIC & AGS User Meeting

  9. Yield in Dh slices: peripheral 0<|Dh|<0.1 0.1<|Dh|<0.3 Au+Au ~ p+p 0.5<|Dh|<0.7 0.3<|Dh|<0.5 RHIC & AGS User Meeting

  10. ridge Yield in Dh slices: 0-20% central 0<|Dh|<0.1 0.1<|Dh|<0.3 0.3<|Dh|<0.5 0.5<|Dh|<0.7 RHIC & AGS User Meeting

  11. Jet induced medium response • Nearside: ridge • Awayside: shoulder • Do they correlate with each other? RHIC & AGS User Meeting

  12. Decomposition method • Fit away side jet with sum of three Gaussians to decompose components: • Head: punch through jet • Shoulder: new peak either side of p (medium response ?!?!) • Treat all components as Gaussian in shape • Use ZYAM method to fix background level RHIC & AGS User Meeting

  13. nearside enhancement vs centrality Enhancement! pp RHIC & AGS User Meeting

  14. shoulder & ridge increase with centrality Yields are very similar! RHIC & AGS User Meeting

  15. Shoulder & ridge pT spectra vs. p+p • Both are softer than hard scattering. • Ridge harder than shoulder? • Shoulder not quite as soft as inclusive hadrons RIDGE SHOULDER RHIC & AGS User Meeting

  16. Where does the momentum go? Phys. Rev. C 77, 011901(R) (2008) • Compare to pp, the awayside per trigger yield at high pT is suppressed. • At lower pT, the awayside yield is enhanced. • During the collision, the total transverse momentum is conserved • How does the jet momentum redistribute into the medium? RHIC & AGS User Meeting

  17. Momentum flow • Weight the per trigger yield of each partner pT bins with <pTassociated> •  Ensemble averaged vector sum of associated particles. Vector sum is along the trigger direction • e.g. partner pT trigger pT projected on trigger pT direction RHIC & AGS User Meeting

  18. Near & away increase with centrality Number of particles pT Weighted yield RHIC & AGS User Meeting

  19. Near = ridge 0.5< Dh <0.7 Near = jet 0 < Dh < 0.1 away/near to ~ cancel acceptance pT is transferred from head  shoulder shoulder to ridge ratio is roughly constant RHIC & AGS User Meeting

  20. Summary • In heavy ion collisions, both the nearside and awayside of the jet are modified • Nearside->ridge • Awayside->shoulder • Both ridge and shoulder are softer than hard scattering and slightly harder than inclusive hadron • The momentum sum of head and shoulder scales with nearside in central Dh region RHIC & AGS User Meeting

  21. Backup slides RHIC & AGS User Meeting

  22. SpassoT,away/ SpassoT,near When we extend the associated particle pT range, the result still holds! RHIC & AGS User Meeting

  23. Weight the integrated yield with pTasso(along trigger particle direction) • both nearside and awayside pTasso is increased • Awayside pTasso increases less than AS yields • Crossover of “head” and “shoulder” at Npart at 150-220 • Charged associated particles only • Not include the trigger particle contribution RHIC & AGS User Meeting

  24. Ratio constant with centrality Consistent with p+p value, also with PYTHIA Even though the total vector sum of nearside/awayside both increase, the ratio of the two still hold constant The ratio of the total contribution from “head” and “shoulder” part is hold, but the contribution from the two is changing. Ratio of Away pTasso / near pTasso PYTHIA head shoulder Head+shoulder RHIC & AGS User Meeting

  25. Extend to Lower pTasso • pTasso =[1.0-5.0] GeV/c • pTasso =[0.5-5.0] GeV/c • The ratio still holds when we include softer particles! RHIC & AGS User Meeting

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