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20-30% 2<pt<2.5. Reaction plane. David L. Winter (Columbia University) for the PHENIX Collaboration. winter@nevis.columbia.edu. Reaction Plane. r=0. r = r( x ). L max. MPC(nucl-th/0503051) Corona effects, E-loss via interactions, p T boost. AMY (JHEP 0305:51 2003) E-loss at high p T.

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  1. 20-30% 2<pt<2.5 Reaction plane David L. Winter (Columbia University) for the PHENIX Collaboration winter@nevis.columbia.edu Reaction Plane r=0 r=r(x) Lmax • MPC(nucl-th/0503051) • Corona effects, E-loss via interactions, pT boost • AMY (JHEP 0305:51 2003) • E-loss at high pT PRL 91, 182301 Introduction …understanding source of significant non-zero v2 (esp in terms of energy loss of jets) is an area of active study • Non-central collisions lead to spatial anisotropy of produced particles. • This gives rise to anisotropy in momentum space… High-pTp0 production with respect to the reaction plane in sNN= 200 GeV Au+Au collisions at PHENIX At low pT, hydro models have successfully described the anisotropy parameter v2, but…. • Studies of in-medium energy loss: • Gyulassy, Vitev, Wang (Phys.Rev.Lett.86:2537,2001) • Shuryak (Phys.Rev.C66:027902,2002) • Drees, Feng, Jia (Phys.Rev.C71:034909,2005) • These are just a few examples… Method p0v2 6 bins (from 0 to p/2) in Df = f-Y Fit with 2nd term in Fourier expansion of anisotropy p0 Red: v2 fit to raw yield Blue: corrected yield Df • Find reaction plane with PHENIX Beam-Beam counter • Measure 0 yield vs angle relative to reaction plane,  • Correct for measured reaction plane resolution. Resolution estimated from two independent Beam-Beam Counter measurements of Y Corrected yields and v2 p0 Suppression vs. Df Using inclusive RAA measurements, we can extract RAA as a function of Df. 19th International Conference on Ultra-Relativistic Nucleus-Nucleus Collisions: 14-20 November 2006 Shanghai, China Results & Discussion Energy loss in GLV formalism: = r0L2 for constant density r0 Significant p0 v2 observed at high pT Using Bjorken 1D expansion where: As a parton propagates a distance Lmax through the medium of density r, how much energy is lost? Question: How does the dependence of RAA on this quantity behave? Comparison with models • Answer: • Low pT single geometric description not sufficient to describe suppression • High pT: RAA collapses to universal dependence 10-20% 50-60% • Summary: • We observe non-trivial p0 v2 at pT up to 10 GeV/c • (High-)pT dependence of v2 consistent with energy loss models • Suppression (RAA) universal dependence on “rLdL” geometric picture at high pT strongly suggests energy loss as dominant mechanism • Is E-loss collisional? Radiative? What is the role of flow & recombination (at high pT)? These measurements can provide valuable input to such study. • Further Reading/Presentations: • M. Shimomura (Poster Session) • K. Miki (Poster Session) • V. S. Pantuev (Parallel 2.2) • Eur.Phys.J.C43:271-280,2005 • nucl-ex/0609019

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