1. Kirill Filimonov, ISMD 2002, Alushta 1 Kirill Filimonov Lawrence Berkeley National Laboratory Anisotropy and high p T hadrons in Au+Au collisions at RHIC Introduction Inclusive spectra Jets and dijets Azimuthal anisotropy at high p T

2. Kirill Filimonov, ISMD 2002, Alushta 2 Jets in heavy ion collisions e+e-  qqbar (OPAL@LEP) p+p  jet+jet (STAR@RHIC) Au+Au  ??? (STAR@RHIC) What Can We See in Au+Au? Leading particles Azimuthal correlations

3. Kirill Filimonov, ISMD 2002, Alushta 3 Leading Particle Suppression leading particle Jets modified in heavy ion collisions? -Leading particle suppression already observed in Au+Au at 130 GeV Nuclear Modification Factor: Glauber Model Partonic Energy loss in high density matter hadrons q q leading particle hadrons leading particle suppressed leading particle suppressed q q

4. Kirill Filimonov, ISMD 2002, Alushta 4 High p T hadrons: Au+Au at RHIC Preliminary  s NN = 200 GeV Excellent quality data from the experiments

5. Kirill Filimonov, ISMD 2002, Alushta 5 Hadron suppression: Au+Au at 200 GeV Preliminary  s NN = 200 GeV PHENIX preliminary QM’02 prelim. data: suppression of factor 4-5 persists to p T =12 GeV/c PHENIX    peripheral and central over measured p+p STAR charged hadrons: central/peripheral

6. Kirill Filimonov, ISMD 2002, Alushta 6 Two-particle correlations at high p T Jet core  x  0.5 x 0.5  look at near-side correlations (  ~0) of high p T hadron pairs Complication: elliptic flow high p T hadrons correlated with the reaction plane orientation also correlated with each other (~v 2 2 ) but elliptic flow has long range correlation (  >> 0.5) Solution: compare azimuthal correlation functions for  and 

7. Kirill Filimonov, ISMD 2002, Alushta 7 Direct evidence for jets  < 0.5  > 0.5 Azimuthal correlation function: Trigger particle p T trig > 4 GeV/c Associate tracks 2 < p T < p T trig Near-side correlation shows jet-like signal in central Au+Au Central Au+Au N.B. Away-side jet contribution subtracted by construction, needs different method…

8. Kirill Filimonov, ISMD 2002, Alushta 8 Suppression of back-to-back pairs Central Au + Au Peripheral Au + Au Near-side well-described Away-side suppression in central collisions Away side jets are suppressed! near side away side STAR Preliminary

9. Kirill Filimonov, ISMD 2002, Alushta 9 Azimuthal anisotropy v 2 Coordinate space: initial asymmetry Momentum space: final asymmetry multiple collisions (pressure) pypy pxpx x y distance of fast parton propogation (energy loss) Jet 1 Jet 2

10. Kirill Filimonov, ISMD 2002, Alushta 10 v 2 predictions at high p T M. Gyulassy, I. Vitev and X.N. Wang PRL 86 (2001) 2537  The value of v 2 at high p t sensitive to the initial gluon density  Saturation and decrease of v 2 as a function of p t at higher p t pQCD inelastic energy loss + parameterized hydro component

11. Kirill Filimonov, ISMD 2002, Alushta 11 Comparison v 2 (p T ) with models (130 GeV) qualitative agreement with “jet-quenching” scenario Adler et al., nucl-ex/0206006, STAR

12. Kirill Filimonov, ISMD 2002, Alushta 12  s dependence at high p T (200/130) STAR preliminary Ratio of spectra 200/130 Ratio of v 2 200/130 Inclusive spectra follow pQCD prediction (XN Wang) minbias v 2 has no energy dependence at p T >2 GeV  surface emission at high p T ? (i.e. strong absorption)

13. Kirill Filimonov, ISMD 2002, Alushta 13 Centrality dependence of v 2 (p T ) v 2 saturates for p T >3 GeV/c for all centralities Indication of geometric origin? (%) PHENIX, preliminarySTAR, preliminary

14. Kirill Filimonov, ISMD 2002, Alushta 14 Comparison with parton cascade 1)Does v 2 saturate for all species? 2)Will v 2 decrease beyond p T =6 GeV/c? D. Molnar 5x minijet multiplicity from HIJING 13x pQCD gg  gg cross section Preliminary

15. Kirill Filimonov, ISMD 2002, Alushta 15 v 2 (p t ) proposed scenario: flavor dependence Baryon production by a non-perturbative mechanism (junctions or hydro) M. Gyulassy, I. Vitev, X.N. Wang and P. Huovinen, Phys. Lett. B 526 (2002) 301-308

16. Kirill Filimonov, ISMD 2002, Alushta 16 STAR Preliminary v 2 of identified hadrons Mesons and baryons show different trend at higher p T Qualitative agreement with the predictions STAR Preliminary PHENIX Preliminary Negatives pi-&K-,pbar

17. Kirill Filimonov, ISMD 2002, Alushta 17 v 2 (p T ) up to 12 GeV/c (STAR) Finite v 2 up to 12 GeV/c in mid- peripheral bin Decrease from saturation level for more central collisions

18. Kirill Filimonov, ISMD 2002, Alushta 18 Summary Jet fragmentation observed, agreement with pQCD Strong suppression of inclusive yields Suppression of back-to-back hadron pairs Azimuthal anisotropy at high p T  large parton energy loss and surface emission? What would large energy loss imply? Partonic or hadronic energy loss? Thermalization? ?