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Near-side di-hadron correlations at RHIC

Near-side di-hadron correlations at RHIC. Jana Bielcikova (Yale University). p T trig =3-6 GeV/c, 2 GeV/c <p T assoc < p T trig. ridge. jet. Dh. Df. J. Putschke (STAR), QM2006. h-h correlation, central Au+Au @ 200 GeV. Outline: Introduction

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Near-side di-hadron correlations at RHIC

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

  2. pTtrig=3-6 GeV/c, 2 GeV/c <pTassoc< pTtrig ridge jet Dh Df J. Putschke (STAR), QM2006 h-h correlation, central Au+Au @ 200 GeV Outline: • Introduction • Properties of ridge and jet-like correlations at near side • Where does the ridge come from? • Summary STAR Preliminary ISMD 2007, Berkeley

  3. 4 <pT(trig)<6 GeV/c 2 GeV/c <pT(assoc)<pT(trig) 0.15 GeV/c <pT(assoc)< 4 GeV/c STAR, PRL 95 (2005) 152301 STAR, Phys Rev Lett 91, 072304 Jet-like correlations at RHIC • disappearance of away-side correlations observed at intermediate pT • lowering associated pT : - 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? ISMD 2007, Berkeley

  4. d+Au, 40-100% D. Magestro, Hard Probes 2004 P. Jacobs, EPJ C43 (2005) 467 3 < pT(trig) < 6 GeV/c2 < pT(assoc) < pT(trig) Au+Au, 0-5% A closer look at near-side peak … Additional near-side correlation in pseudo-rapidity () observed STAR, PRC73 (2006) 064907, J.Phys.G32 (2006) 37 pT < 2 GeV/c The near-side jet interacts with the medium! ISMD 2007, Berkeley

  5. The ridge properties ISMD 2007, Berkeley

  6. (J) ||<0.7 (J) ||<0.7 2 1 const bkg. subtracted 2 const bkg. subtracted (J+R) - (R)  v2 subtracted (J+R) ||<1.7 (J+R) ||<1.7 (J) no v2 subtraction needed Extracting near-side “jet” and “ridge” yields pTtrig=3-4 GeV/c, pTassoc>2 GeV/c J = “jet”, R= “ridge” J. Putschke (STAR),QM’2006 ISMD 2007, Berkeley

  7. after v2 subtraction jet+ridge 3 GeV/c < pTtrigger< 4 GeV/c and pTassoc> 2 GeV/c STAR preliminary  Jet+Ridge () Jet () Jet) yield,)   jet ridge  ridge Npart Centrality dependence of near-side yield (I) J. Putschke (STAR),QM2006 • jet yield independent of centrality (Npart) • ridge yield increases ~ linearly with Npart ISMD 2007, Berkeley

  8. Jet Jet + Ridge Ridge Jet Centrality dependence of near-side yield (II) -> “ridge” yield increases with centrality ridge for K0S trigger < ridge for Λtrigger • steep increase of near-side yield with centrality in Au+Au • ratio of yields in central Au+Au/d+Au ~ 4-5 J.B. (STAR), QM’2006 -> “jet” yield is independent of centrality and agrees with d+Au ISMD 2007, Berkeley

  9. STAR preliminary C. Zhang, J. Jin (PHENIX), QM2006 STAR preliminary 8 <pTtrig< 15 GeV/c 8 <pTtrig< 15 GeV/c pT spectra of associated particles at near side • increase of near-side yield • at low pTassoc (zT) observed by • STAR and PHENIX • subtraction of Dh-independent • ‘ridge-yield’ recovers • centrality-independent jet yield STAR preliminary |h|<0.35 zT = pTassoc/pTtrig M. Horner (STAR), QM2006 |h|<1.0 STAR preliminary ISMD 2007, Berkeley

  10. “jet” slope ridge slope inclusive slope STAR preliminary Ridge Jet pTtrig (GeV/c) pT spectra of associated particles J. Putschke (STAR),QM’2006 STAR preliminary Ridge/Jet yield (pTassoc > pTassoc,cut) pTassoc.cut (GeV/c) • jet spectrum harder than inclusive pT-spectrum • T(jet) increases with pTtrigger • x • ridge spectrum similar to particles from bulk • T(ridge) ~ independent of pTtrigger ISMD 2007, Berkeley

  11. pTtrigger dependence of ridge pT assoc> 2 GeV/c STAR preliminary J. Putschke (STAR),QM’2006 Ridge yield: persists up to pTtrig~ 10 GeV/c  Ridge is independent of jet energy ISMD 2007, Berkeley

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

  13. System size dependence of ridge yield relative ridge yield = ridge yield / jet() J. Putschke (STAR), QM2006 pTassoc. > 2 GeV/c STAR preliminary Au+Au @ 200 GeV Cu+Cu @ 200 GeV Au+Au @ 200 GeV (30-40 %) Cu+Cu @ 200 GeV (0-10 %) relative ridge yield relative ridge yield 3 GeV/c <pTtrigger<4 GeV/c STAR preliminary Relative ridge yield comparable in Au+Au and Cu+Cu at same Npart ISMD 2007, Berkeley

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

  15. Is there ridge at forward rapidity? L. Molnar (STAR), QM’06, nucl-ex/0701061 pTassoc = 0.2-2.0 GeV/c: no near-side peak within systematic errors pTassoc > 1 GeV/c: : data suggest a non-zero correlation at near side (?) ISMD 2007, Berkeley

  16. Where does the ridge come from? ISMD 2007, Berkeley

  17. Parton recombination C. Chiu & R. Hwa, Phys. Rev. C72 (2005) 034903 • hard parton passing through the medium enhances thermal parton distribution (ΔT=15 MeV)  recombination of thermal partons forms a pedestal (‘ridge’) • enhanced baryon/meson ratio jet ridge ISMD 2007, Berkeley

  18. Parton radiation and its coupling to longitudinal flow 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 Dh ISMD 2007, Berkeley

  19. Longitudinal broadening of quenched jets in turbulent color fields 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 Dh but not inDf wide ridge in rapidity at low pTassoc ISMD 2007, Berkeley

  20. Momentum broadening in anisotropic QGP • P. Romatschke, Phys.Rev. C75, 014901 (2007) • momentum broadening in a homogeneous • but locally anisotropic system • calculation: eccentricity ~ √8/3 • kz/kT ~ 3 • caveats: • - calculation done only for charm quark and • collisional energy loss • - requires large anisotropy (ξ ~ 10) •  large shear viscosity(ξ~ 10h/stT) • but data suggest low shear viscosity (~0.1) kz/kT≃Δη/Δf > 1 data: D. Magestro (STAR), Hard Probes 2004 ISMD 2007, Berkeley

  21. model r data STAR preliminary J.Putschke (STAR), QM2006 f1 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 f1  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) ISMD 2007, Berkeley

  22. Momentum kick model C.-Y. Wong , hep-ph/0707.2385 • partons in medium acquire momentum ‘kick’ from propagating jet • fix T = 470 MeV, vary q1 (mom. kick) or σy (rapidity distribution) • narrow peak in Df depends mainly on momentum kick • ridge structure in Dh depends on initial parton rapidity distribution q1=0.6 GeV/c sy= 5 ISMD 2007, Berkeley

  23. Summary Existence of ridge-like correlations at near side is well established and measured: - particles associated with the ridge are similar to bulk (pT 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! ISMD 2007, Berkeley

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