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The story of v 3

The story of v 3. John Chin-Hao Chen ( 陳勁豪 ) for PHENIX Collaboration Stony Brook University Moriond QCD 2011/03/23. outline. What is v 3 ? How to measure v 3 ? How do theorist think of v 3 ? Does v 3 explains the jet shape modification (ridge and shoulder)?. v n : particle anisotropy.

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The story of v 3

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  1. The story of v3 John Chin-Hao Chen (陳勁豪) for PHENIX Collaboration Stony Brook University Moriond QCD 2011/03/23 John Chin-Hao Chen

  2. outline • What is v3? • How to measure v3? • How do theorist think of v3? • Does v3 explains the jet shape modification (ridge and shoulder)? John Chin-Hao Chen

  3. vn: particle anisotropy • Spatial distribution of colliding area is “almond” like due to overlap of two colliding nuclei. • dN/d(f-y) =N0(S(1+2vncosn(f-y))) • v2 = elliptic flow • If nuclei is perfect spherical-> no vodd • With some initial state fluctuation -> finite vodd? John Chin-Hao Chen

  4. Glauber initial state • The nuclear is not perfect in shape • Nucleon distribution is not smooth • Azimuthal symmetry no longer holds • vodd is possible John Chin-Hao Chen

  5. 2-D Dh-Df correlations Peripheral Au+Au/pp Central Au+Au Dh Dh shoulderridge Df Df rad Both near and away side are modified! John Chin-Hao Chen

  6. v3, reason for ridge and shoulder? • Ridge sits at Df ~ 0, shoulder sits at Df~2p/3, 4p/3 • A 3-peak structure! • v3 (Fourier Coefficient of thecos3Df term) gives a natural 3-peak structure • Is v3 the explanation? • Need to measure v3 to answer this question! John Chin-Hao Chen

  7. How do we measure v3? • Reaction plane method • Use forward detector to determine the n-th reaction plane • Two particle correlation method • No need to determine the reaction plane • central-central two particle correlations John Chin-Hao Chen

  8. S. Esumi, WWND2011 John Chin-Hao Chen

  9. Measuring vn with yn • Use the forward detector to determine the nth event plane, yn • Measure vn respect to yn and correct with reaction plane resolution sn John Chin-Hao Chen

  10. S. Esumi, WWND2011 John Chin-Hao Chen

  11. vn from two particle correlations • Standard v2(v4): single particle vs. reaction plane dN/d(f-y) • Can also measure vn via two particle correlation • Central-central correlation (0.3<|Dh|<0.7) • PHENIX: Phys. Rev. Lett. 89, 212301 (2002) • dNAB/dDf = N(1+ S(2Cncos(nDf))), Cn = vnAvnB • the two particles are in the same event, therefore share the same reaction plane • When pTA = pTB, vn = sqrt(Cn) • With low partner pT (below 1 GeV), the jet contribution can be ignored, but not at high pT John Chin-Hao Chen

  12. v2{2p}, v3{2p} from two particle correlations v2{2p}, v3{2p}, • v2{2p} agrees with previous PHENIX measurements at low pT • v3{2p} • Nonzero • Increases with pT (NB: may have non-flow effects in this method) • Increases with centrality Dash line is PHENIX v2 measured by event plane Phys. Rev. Lett. 105, 062301 (2010) John Chin-Hao Chen

  13. Compare with v3 measured by y3 v3 2P RP • 2-particle (small Dh) v3 higher than reaction plane (large Dh) v3 • should expect non-flow contribution i.e. jets John Chin-Hao Chen

  14. Large h gap measurement (bulk only) agrees well with hydro prediction! Compare with Hydro calculation John Chin-Hao Chen

  15. What about non-flow in v3? • Use jets in p+p to calibrate! • Do a Fourier analysis of the per trigger yield jet function • JF = SCn cos(nDf) • For Au+Au: combinatorial background “b0(1+2v2trigv2partcos2Df)” removed via ZYAM • ZYAM will not change any Fourier coefficients, except C0 and C2 • Various centrality and partner pT bins for initial insights into bulk vs. jet contributions John Chin-Hao Chen

  16. Baseline comparison • Dijet (pp) and away-side suppressed dijet • pp tells us the pure jet contribution • pp nearside only: the awayside jet is fully suppressed • The jets in AuAu (nearside jet + “head”) should fall in between. • Fourier strength beyond this is not from the jets. • Jet-bulk contribution! • v2 of bulk (background) flow subtracted when making the jet function John Chin-Hao Chen

  17. Fourier Spectra of Jet Function v3 from jet+bulk+jet-medium int.? v3 from jet • No significant contribution above c4 • Removing the awayside pp enhances the codd terms • The c3 in AuAu has contributions from both jet and bulk! John Chin-Hao Chen

  18. summary • v2, v3 and v4 are measured with yn and two particle correlations. • v3 measured by two particle correlations (small h gap) are consistent with but larger than reaction plane method (large h gap) • v3 from reaction plane method agrees with hydro prediction • The third Fourier coefficient in jet function is significantly enhanced in central AuAu collisions due to the v3 from bulk, but also have some contributions from the jet John Chin-Hao Chen

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