1. Jana Bielcikova (Yale)ISMD 2007, Berkeley1 Near-side di-hadron correlations at RHIC Jana Bielcikova (Yale University)

2. Jana Bielcikova (Yale)ISMD 2007, Berkeley2 Outline: Introduction Properties of ridge and jet-like correlations at near side Where does the ridge come from? Summary p T trig =3-6 GeV/c, 2 GeV/c <p T assoc < p T trig jet ridge   h-h correlation, central Au+Au @ 200 GeV J. Putschke (STAR), QM2006 STAR Preliminary

3. Jana Bielcikova (Yale) ISMD 2007, Berkeley 3 Jet-like correlations at RHIC 0.15 GeV/c <p T (assoc)< 4 GeV/c2 GeV/c <p T (assoc)<p T (trig) 4 <p T (trig)<6 GeV/c STAR, Phys Rev Lett 91, 072304 STAR, PRL 95 (2005) 152301 disappearance of away-side correlations observed at intermediate p T lowering associated p T : - resurrects correlated yield at away side - near and away-side yields are enhanced with respect to p+p/d+Au - shape of the away-side peak is not Gaussian Mach cone? Deflected jets? Cherenkov radiation?

4. Jana Bielcikova (Yale) ISMD 2007, Berkeley 4 A closer look at near-side peak … STAR, PRC73 (2006) 064907, J.Phys.G32 (2006) 37 p T < 2 GeV/c d+Au, 40-100%Au+Au, 0-5% 3 < p T (trig) < 6 GeV/c 2 < p T (assoc) < p T (trig) D. Magestro, Hard Probes 2004 P. Jacobs, EPJ C43 (2005) 467 Additional near-side correlation in pseudo-rapidity (  ) observed The near-side jet interacts with the medium!

5. Jana Bielcikova (Yale) ISMD 2007, Berkeley 5 The ridge properties

6. Jana Bielcikova (Yale)ISMD 2007, Berkeley6  (J+R) |  |<1.7 J = “jet”, R= “ridge”  (J+R) |  |<1.7 v 2 subtracted Extracting near-side “jet” and “ridge” yields 1 2 2 const bkg. subtracted  (J) |  |<0.7   (J+R) -  (R)  (J) no v 2 subtraction needed const bkg. subtracted  (J) |  |<0.7 p T trig =3-4 GeV/c, p T assoc >2 GeV/c J. Putschke (STAR),QM’2006

7. Jana Bielcikova (Yale) ISMD 2007, Berkeley7 Centrality dependence of near-side yield (I) STAR preliminary Jet+Ridge (  ) Jet (  ) Jet  ) yield ,  ) N part 3 GeV/c 2 GeV/c jet yield independent of centrality (N part ) ridge yield increases ~ linearly with N part  ridge    ridge jet jet+ridge after v 2 subtraction J. Putschke (STAR),QM2006

8. Jana Bielcikova (Yale) ISMD 2007, Berkeley8 steep increase of near-side yield with centrality in Au+Au ratio of yields in central Au+Au/d+Au ~ 4-5 -> “jet” yield is independent of centrality and agrees with d+Au JetJet + Ridge -> “ridge” yield increases with centrality ridge for K 0 S trigger < ridge for Λ  trigger Ridge Centrality dependence of near-side yield (II) Jet J.B. (STAR), QM’2006

9. Jana Bielcikova (Yale) ISMD 2007, Berkeley 9 p T spectra of associated particles at near side M. Horner (STAR), QM2006 increase of near-side yield at low p T assoc (z T ) observed by STAR and PHENIX subtraction of  -independent ‘ridge-yield’ recovers centrality-independent jet yield z T = p T assoc /p T trig STAR preliminary C. Zhang, J. Jin (PHENIX), QM2006 STAR preliminary 8 <p T trig < 15 GeV/c STAR preliminary |  |<0.35 |  |<1.0

10. Jana Bielcikova (Yale) ISMD 2007, Berkeley 10 STAR preliminary Ridge Jet Ridge/Jet yield (p T assoc > p T assoc,cut ) p T spectra of associated particles jet spectrum harder than inclusive p T -spectrum T(jet) increases with p T trigger x ridge spectrum similar to particles from bulk T(ridge) ~ independent of p T trigger p T assoc.cut (GeV/c) STAR preliminary “jet” slope ridge slope inclusive slope p T trig (GeV/c) J. Putschke (STAR),QM’2006

11. Jana Bielcikova (Yale) ISMD 2007, Berkeley 11 p T trigger dependence of ridge p T assoc > 2 GeV/c STAR preliminary Ridge yield: persists up to p T trig ~ 10 GeV/c  Ridge is independent of jet energy J. Putschke (STAR),QM’2006

12. Jana Bielcikova (Yale) ISMD 2007, Berkeley12 Particle composition in jet and ridge A hint? Ridge: B/M ratio closer to bulk Jet: B/M ratio ~ p+p More data needed ! J.B. (STAR), WWND 2007

13. Jana Bielcikova (Yale) ISMD 2007, Berkeley13 Relative ridge yield comparable in Au+Au and Cu+Cu at same N part p T assoc. > 2 GeV/c STAR preliminary relative ridge yield relative ridge yield = ridge yield / jet(  ) Au+Au @ 200 GeV Cu+Cu @ 200 GeV 3 GeV/c <p T trigger <4 GeV/c Au+Au @ 200 GeV (30-40 %) Cu+Cu @ 200 GeV (0-10 %) System size dependence of ridge yield J. Putschke (STAR), QM2006

14. Jana Bielcikova (Yale) ISMD 2007, Berkeley14 Energy content in the ridge STAR, Phys. Rev. Lett. 95 (2005) 15230, J. Putschke (STAR), QM2006 0.15 < p t,assoc < 4 GeV/c 4 < p t,trigger < 6 GeV/c 6 < p t,trigger < 10 GeV/c “Ridge energy” “Ridge energy” } } near-side modification in published results also due to ridge energy content deposited in the ridge is few GeV

15. Jana Bielcikova (Yale) ISMD 2007, Berkeley15 L. Molnar (STAR), QM’06, nucl-ex/0701061 Is there ridge at forward rapidity? p T assoc = 0.2-2.0 GeV/c: no near-side peak within systematic errors p T assoc > 1 GeV/c: : data suggest a non-zero correlation at near side (?)

16. Jana Bielcikova (Yale) ISMD 2007, Berkeley16 Where does the ridge come from?

17. Jana Bielcikova (Yale) ISMD 2007, Berkeley17 C. Chiu & R. Hwa, Phys. Rev. C72 (2005) 034903 hard parton passing through the medium enhances thermal parton distribution ( Δ T=15 MeV)  recombination of thermal partons forms a pedestal (‘ridge’) enhanced baryon/meson ratio Parton recombination ridge jet

18. Jana Bielcikova (Yale) ISMD 2007, Berkeley18 N. Armesto, C.A. Salgado, U.A. Wiedemann, Phys. Rev. Lett. 93 (2004) parton energy loss is sensitive to energy density of medium + collective flow medium induced gluon radiation radiated gluon contributes to broadening in  Parton radiation and its coupling to longitudinal flow

19. Jana Bielcikova (Yale) ISMD 2007, Berkeley19 A. Majumder, B. Mueller, S.A.Bass hep-ph/0611135 plasma instabilities in longitudinally expanding medium  non-thermal color fields  broadening of jet cone in   but not in   wide ridge in rapidity at low p T assoc Longitudinal broadening of quenched jets in turbulent color fields

20. Jana Bielcikova (Yale) ISMD 2007, Berkeley20 P. Romatschke, Phys.Rev. C75, 014901 (2007) momentum broadening in a homogeneous but locally anisotropic system calculation: eccentricity ~ √8/3   z /  T ~ 3 caveats: - calculation done only for charm quark and collisional energy loss - requires large anisotropy (ξ ~ 10)  large shear viscosity (ξ~ 10  /s  T) but data suggest low shear viscosity (~0.1) Momentum broadening in anisotropic QGP  z /  T ≃  Δη  /  Δ  > 1 data: D. Magestro (STAR), Hard Probes 2004

21. Jana Bielcikova (Yale) ISMD 2007, Berkeley21 Correlations between jet and radial flow S. Voloshin, nucl-th/0312065, Nucl.Phys. A749, 287 (2005) E. Shuryak, nucl-th/0706.3531 transverse radial expansion in central collisions correlation appears due to jet quenching averaging over jet origin and  1  width broader than that in data ridge is independent of jet particle spectra in ridge: points of origin are biased towards surface  ‘a bit’ stiffer slope than that of bulk particle composition: N(baryons)>N(mesons) model data r 11 J.Putschke (STAR), QM2006 STAR preliminary

22. Jana Bielcikova (Yale) ISMD 2007, Berkeley22 Momentum kick model C.-Y. Wong, hep-ph/0707.2385 partons in medium acquire momentum ‘kick’ from propagating jet fix T = 470 MeV, vary q 1 (mom. kick) or σ y (rapidity distribution) narrow peak in  depends mainly on momentum kick ridge structure in  depends on initial parton rapidity distribution q 1 =0.6 GeV/c  y = 5

23. Jana Bielcikova (Yale) ISMD 2007, Berkeley23 Summary Existence of ridge-like correlations at near side is well established and measured: - particles associated with the ridge are similar to bulk (p T spectra, particle composition) - more data are becoming available for identified particles - studies with 3-particle correlations ongoing (2+1, 1+2) - studies at forward rapidity These are important measurements to pin down the physics origin of the ridge BUT More quantitative theoretical predictions are needed as well!