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2011/03/23 Moriond QCD 2011John Chin-Hao Chen1 The story of v 3 John Chin-Hao Chen ( 陳勁豪 ) for PHENIX Collaboration Stony Brook University Moriond QCD 2011/03/23

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2011/03/23 Moriond QCD 2011John Chin-Hao Chen2 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)?

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2011/03/23 Moriond QCD 2011John Chin-Hao Chen3 v n : particle anisotropy Spatial distribution of colliding area is “almond” like due to overlap of two colliding nuclei. dN/d( - ) =N 0 ( (1+2v n cosn( - ))) v 2 = elliptic flow If nuclei is perfect spherical-> no v odd With some initial state fluctuation -> finite v odd ?

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2011/03/23 Moriond QCD 2011John Chin-Hao Chen4 Glauber initial state The nuclear is not perfect in shape Nucleon distribution is not smooth Azimuthal symmetry no longer holds v odd is possible

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2011/03/23 Moriond QCD 2011John Chin-Hao Chen5 2-D correlations shoulder ridge rad Peripheral Au+Au/pp Central Au+Au Both near and away side are modified!

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2011/03/23 Moriond QCD 2011John Chin-Hao Chen6 v 3, reason for ridge and shoulder? Ridge sits at ~ 0, shoulder sits at ~2 /3, 4 /3 –A 3-peak structure! v 3 (Fourier Coefficient of the cos3 term) gives a natural 3-peak structure Is v 3 the explanation? Need to measure v3 to answer this question!

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2011/03/23 Moriond QCD 2011John Chin-Hao Chen7 How do we measure v 3 ? 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

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2011/03/23 Moriond QCD 2011John Chin-Hao Chen8 S. Esumi, WWND2011

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2011/03/23 Moriond QCD 2011John Chin-Hao Chen9 Measuring v n with n Use the forward detector to determine the nth event plane, n Measure v n respect to n and correct with reaction plane resolution n

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2011/03/23 Moriond QCD 2011John Chin-Hao Chen10 S. Esumi, WWND2011

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2011/03/23 Moriond QCD 2011John Chin-Hao Chen11 v n from two particle correlations Standard v 2 (v 4 ): single particle vs. reaction plane dN/d( Can also measure v n via two particle correlation –Central-central correlation (0.3<| |<0.7) –PHENIX: Phys. Rev. Lett. 89, 212301 (2002) –dN AB /d = N(1+ (2C n cos(n ))), C n = v n A v n B the two particles are in the same event, therefore share the same reaction plane When p T A = p T B, v n = sqrt(C n ) With low partner p T (below 1 GeV), the jet contribution can be ignored, but not at high p T

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2011/03/23 Moriond QCD 2011John Chin-Hao Chen12 v 2 {2p}, v 3 {2p} from two particle correlations v 2 {2p} agrees with previous PHENIX measurements at low p T v 3 {2p} –Nonzero –Increases with p T (NB: may have non-flow effects in this method) –Increases with centrality v 2 {2p}, v 3 {2p}, Dash line is PHENIX v 2 measured by event plane Phys. Rev. Lett. 105, 062301 (2010)

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2011/03/23 Moriond QCD 2011John Chin-Hao Chen13 2-particle (small ) v 3 higher than reaction plane (large v 3 should expect non-flow contribution i.e. jets Compare with v 3 measured by 3 RP 2P v3v3

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2011/03/23 Moriond QCD 2011John Chin-Hao Chen14 Compare with Hydro calculation Large gap measurement (bulk only) agrees well with hydro prediction!

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2011/03/23 Moriond QCD 2011John Chin-Hao Chen15 What about non-flow in v 3 ? Use jets in p+p to calibrate! Do a Fourier analysis of the per trigger yield jet function –JF = C n cos(n ) –For Au+Au: combinatorial background “b 0 (1+2v 2 trig v 2 part cos2 )” removed via ZYAM –ZYAM will not change any Fourier coefficients, except C 0 and C 2 Various centrality and partner p T bins for initial insights into bulk vs. jet contributions

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2011/03/23 Moriond QCD 2011John Chin-Hao Chen16 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! v 2 of bulk (background) flow subtracted when making the jet function

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2011/03/23 Moriond QCD 2011John Chin-Hao Chen17 Fourier Spectra of Jet Function v 3 from jet v 3 from jet+bulk+ jet-medium int.? No significant contribution above c4 Removing the awayside pp enhances the c odd terms The c 3 in AuAu has contributions from both jet and bulk!

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2011/03/23 Moriond QCD 2011John Chin-Hao Chen18 summary v 2, v 3 and v 4 are measured with n and two particle correlations. v 3 measured by two particle correlations (small gap) are consistent with but larger than reaction plane method (large gap) v 3 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 v 3 from bulk, but also have some contributions from the jet

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