1. TWO PARTICLE CORRELATION MEASUREMENTS AT PHENIX Takahito Todoroki For the PHENIX Collaboration University of Tsukuba & RIKEN Nishina Center Hard Probes 2012 at Cagliari, Italy 28 May 2012Hard Probes 2012 1

2. Contents Higher harmonic event plane and flow(v n ) Correlations with v n subtractions Correlations relative to event plane - At high and intermediate p T Summary 28 May 2012Hard Probes 2012 2

3. Motivations Dissect possible interplay of hard- scattered partons & hot dense medium To have definitive answer what remains in correlations after v n subtractions To test path length dependence of parton energy loss via correlations relative to event plane 28 May 2012Hard Probes 2012 3

4. Initial state of collisions Initial collision geometry - Smooth to Fluctuating picture Azimuthal particle distribution  v n(even)    only v n(even)  n  + v n(odd)  n  Smooth picture Fluctuating picture  28 May 2012Hard Probes 2012 4

5. v 3 is comparable to v 2 at 0~10% v 2 evolution as centrality increment, no evolution in v 3 v 4 {  4 } ~ 2 x v 4 {  2 } Charged particle v n : |  |<0.35 Event plane  n : |  |=1.0~2.8 PRL.107.252301 Charged Hadron v n at PHENIX 28 May 2012Hard Probes 2012 5

6. Identified Particle v n Mass dependence at low p T : Hydrodynamics Baryon/Meson diff. at mid p T : Quark Coalescence 28 May 2012Hard Probes 2012 6

7. v n contributions in correlations Contributions from v n : Ridge & Shoulder positions : Agree with v 3 peaks v n subtractions needed to get real jet correlations Ridge 2< p T asso < p T trig GeV/C Phys. Rev. C 80, 064912 (2009) Phys. Rev. C 78, 014901 (2008) ○:p+p ●: Au+Au Shoulder v 2 subtracted n=3 28 May 2012Hard Probes 2012 7

8. Correlations with  gap v n reproduce Ri dge & Shoulder at 0-5% Track at  with EP from full FCAL  v n with EP Method v n with 2Par. Cor Method Charged particle pair with large rapidity gap e.g.  Pb+Pb 2.76TeV No Flow Subtraction ￮ measured correlations 28 May 2012Hard Probes 2012 8 QM’11 J. Jia ATLAS Flow Plenary

9. Correlations without  gap Away side shoulders are almost gone in most-central collisions 0-20% Incl.  - hadron 2-3x1-2 GeV/c PHENIX PRELIMINARY Au+Au 200GeV 0-20% 28 May 2012Hard Probes 2012 9 

10. Correlations up to centrality 50% Away side shoulders - Canceled in most-central collisions : 0-10% - Remain in mid-central collisions : 20-50% To Do : Include v1 term to v n modulation for definitive answer V 2, V 3 & V 4 (   ) modulation by ZYAM method 28 May 2012Hard Probes 2012 10

11. Correlations relative to event plane Control parton path length - By selecting trigger relative to forward event plane - Reduce autocorrelations of jet itself tt aa  nn ss Mid rapidity Forward rapidity 28 May 2012Hard Probes 2012 11

12. High p T range Near side yield : No suppression Away side yield : Monotonic decrease I AA = Y AA /Y pp Short path length Long path length PRC.84.024904 28 May 2012Hard Probes 2012 12 v 2 & v 4 {   } modulated Au+Au 200GeV 20-60%

13. Intermediate p T range Constant suppression of back-to-back jet Two competitive effects seen  2 R.P. Trig. in-plane trigger case out-of-plane trigger case Au+Au 200GeV 20-50% h-h :2-4x1-2GeV/c v 2 & v 4 {   } modulated 28 May 2012Hard Probes 2012 13 PHENIX preliminary Flow subtracted yield is shown radially with base line. penetration dominance surface dominance

14. Summary Higher harmonic flow v n has been measured By v n modulation to correlations, - Shoulders almost gone in most-central collisions - Shoulders remain in mid-central collisions Correlations relative to event plane - Monotonic away side suppression at high p T - Constant suppression of di-jet & Two competitive effects at intermediate p T Fully v n modulated analyses are in progress 28 May 2012Hard Probes 2012 14

15. Backup Slides 28 May 2012Hard Probes 2012 15

16.  i -  j correlations 28 May 2012Hard Probes 2012 16 PRL.107.252301

17. v n via event plane method Mid rapidity particle anisotropy relative to forward event planes 05-5 ZDC/SMD  dN/d  RXN in: 1.5<|  |<2.8 & out: 1.0<|  |<1.5 MPC: 3.1<|  |<3.7 BBC: 3.0<|  |<3.9 CNT: |  |<0.35 2cm Pb converter in front 28 May 2012Hard Probes 2012 17 RXN

18. Degeneracy among models disentangled by v 3 v 3 seems to prefer low viscosity  Glauber+  s  works better  CGC-KLN+  s  failed More constraints to hydrodynamics calculations V2V2 V3V3 PRL.107.252301 (ppg132) B. Alver et. al., PRC82, 034913(2010). B. Schenke et. al., PRL106, 042301(2011). H. Petersen et. al., PRC82, 041901(2010). (Event Plane Method) 28 May 2012Hard Probes 2012 18

19. 28 May 2012Hard Probes 2012 19 QM’11 J. Jia ATLAS Flow Plenary

20. Scaling property of v 2 28 May 2012Hard Probes 2012 20

21. Scaling property of v n v n (KE T /n q )/n q failed on v 3, v 4 & v 4 {   } v n (KE T /n q )/n q n/2 : need correction power 28 May 2012Hard Probes 2012 21

22. Fourier decomposition of flow subtracted correlations 28 May 2012Hard Probes 2012 22

23. Correlations relative to   28 May 2012Hard Probes 2012 23