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Medium properties and jet-medium interaction from STAR

Medium properties and jet-medium interaction from STAR. Jana Bielcikova for the STAR Collaboration NPI ASCR and Center for physics of ultra-relativistic heavy-ion collisions, Prague, Czech Republic.

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Medium properties and jet-medium interaction from STAR

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  1. Medium properties and jet-medium interaction from STAR Jana Bielcikova for the STAR Collaboration NPI ASCR and Center for physics of ultra-relativistic heavy-ion collisions, Prague, Czech Republic XLIII Rencontres de Moriond “QCD and High EnergyInteractions”

  2. Outline: • Introduction • “Jet”-medium interaction via 2- and 3-particle correlations - conical emission ? - long range pseudo-rapidity correlations (“ridge”) • Summary XLIII Rencontres de Moriond

  3. trigger associated A+A  flow p+p associated Probing QCD matter with jets Au+Au p+p What happens to high-pT particles/jets which pass through the medium? Are they similar to p+p or modified by the medium? near-side away-side Full jet reconstruction in A+A collisions at RHIC difficult due to underlying background  use azimuthal correlations of high-pT particles XLIII Rencontres de Moriond

  4. Jet-like correlations at RHIC 4 <pT(trig)<6 GeV/c 2 GeV/c <pT(assoc)<pT(trig) 0.15<pT(assoc)<4.0 GeV/c STAR, PRL 95 (2005) 152301 STAR, PRL 91 (2003) 072304 • central Au+Au collisions @ 200 GeV: • disappearance of away-side correlations observed at intermediate pT • d+Au and p+p similar -> jet suppression is a final state effect • lowering associated pT resurrects correlated yield • - enhanced yield at near and away side + shape modification XLIII Rencontres de Moriond

  5. 40-60% Preliminary 0-12% Conical emission in A+A collisions? 2.5 < pTtrig< 4 GeV/c and 1< pTassoc < 2.5 GeV/c • Mach cone in heavy-ion physics introduced • in1970’s (Hofmann, Stöcker, Heinz, Scheid, Greiner) • a supersonic parton creates shock waves: • - hydrodynamics • Stöcker et al., NPA750 (2005) 121 • Casalderrey-Solana et al., NPA774 (2006) 577 • Renk, Ruppert, PRC73 (2006) 011901 • - colored plasma • Ruppert, Mueller, PLB618 (2005) 123 • - AdS/CFT • Gubser, Pufu, Yarom, PRL100, (2008) 012301 • Čerenkov gluon radiation by a superluminal parton • Dremin, NPA750 (2006) 233 • Koch et. al., PRL96 (2006) 172302 M. Horner (STAR), J.Phys.G34, S995,2007 To distinguish from other mechanisms 3-particle correlation studies needed XLIII Rencontres de Moriond

  6. near near near Medium Medium Medium away away π away di-jets 0 π 0 deflected jets mach cone Conical flow or deflected jets? (I) cartoons of 3-particle azimuthal correlations (1 trigger + 2 associated particles) di-jets conical emission deflected jets (by the collective movement, “flow”, of the expanding medium) Armesto , Salgado, Wiedemann, PRL 93, (2004) 242301 XLIII Rencontres de Moriond

  7. C3  STAR Preliminary  Subtraction of v2v2v4 terms using v2 = 0.06 Subtraction of v2v2v4 term using v2 = 0.12 Conical flow or deflected jets? (II) • STAR uses 2 methods: • 1. Jet+flow background - model dependent analysis • evidence for conical emission • 2. Cumulantmethod • C. Pruneau (STAR),J.Phys.G34 (667),2007; • C. Pruneau, PRC 74 (2006) 064910 • unambiguous evidence • for 3-particle correlations • strength and shape of away-side • structures depend on magnitude • of flow coefficients • no conclusive evidence for • conical emission d+Au central Au+Au STAR Preliminary STAR Preliminary Note: Large and complicated backgrounds J. Ulery (STAR), arXiv:0704.0224 3 < pT,trig < 4 GeV/c 1 < pT,assoc < 2 GeV/c central Au+Au central Au+Au STAR Preliminary 

  8. Mach cone or Čerenkov gluons? Mach cone cone angle independent of pTassoc Čerenkov gluon radiation: cone angle decreases with pTassoc STAR preliminary Cone angle (radians) pT(GeV/c) pTdependence of cone angle favors Mach coneover Čerenkov gluon emission Koch, Majumder, Wang, PRL96 172302 (2006) XLIII Rencontres de Moriond

  9. Momentum conservation in correlation analyses C3 cumulant pTconservation 3-particle correlation Calculation for: <pT,trig > = 3.2 GeV/c <pT,assoc >= 1.2 GeV/c N. Borghini, PRC 75 (2007) 021904 Calculation by N. Borghini: momentum conservation  sizable correlation between pairs or triplets of high-pT particles in central Au+Au collisions at RHIC  C3(pT) ~ C3(flow)  jet “distorts” the event needs to be evaluated in the data 2-particle correlation after v2 subtraction N. Borghini, arXiv:0710.2588 XLIII Rencontres de Moriond

  10. A closer look at the near-side peak … pTtrig=3-6 GeV/c, 2 GeV/c <pTassoc< pTtrig d+Au, 200 GeV Au+Au, 200 GeV STAR preliminary “jet” ridge Additional near-side correlation in  observed in central Au+Au collisions • What is the ridge? • 1) Medium heating and parton recombination • Chiu & Hwa PRC 72 (2005) 034903 • 2) Radial flow + high-pT trigger particle • Shuryak, Phys.Rev.C76 (2007) 047901 • Voloshin, nucl-th/0312065 NPA 749, (2005) 287 • 3) Parton radiation and its coupling • to the longitudinal flow • Armesto, Salgado, Wiedemann, PRL 93 (2004) 242301 4) Momentum broadening in anisotropic QGP Romatschke, PRC 75 (2007) 014901 5) Longitudinal broadening of quenched jets in turbulent color fields Majumder, Mueller, Bass, PRL99 (2007) 042301 6) Momentum kick imparted on partons in medium Wong, PRCPRC76 (2007) 054908 XLIII Rencontres de Moriond

  11. after v2 subtraction jet+ridge    jet ridge  ridge Centrality and system size dependence of near-side yield • “jet” yield independent of colliding system, • Npart and trigger particle type • ridge yield increases with Npart Au+Au: J. B. (STAR), QM 2006 Cu+Cu: C. Nattrass (STAR), QM2008 XLIII Rencontres de Moriond

  12. “Jet” and ridge: pT dependence pT assoc> 2 GeV/c Ridge: solid symbols Jet: open symbols J. Putschke (STAR), J.Phys.G34:S679 (2007) STAR preliminary J. Putschke (STAR), J.Phys.G34:S679 (2007) Jet: T(jet) > T(bulk) T(jet) increases with pTtrig Ridge: T(ridge) ~ T(bulk) T(ridge) ~ independent of pTtrig ridge persists up to pTtrig~ 10 GeV/c “jet” slope ridge slope inclusive slope h-h correlations pTassociated>2GeV/c “jet” slope ridge slope inclusive slope STAR preliminary XLIII Rencontres de Moriond

  13. Particle composition in “jet” and ridge “Jet” Cone vs. Inclusive Ridge vs. Inclusive STAR Preliminary STAR Preliminary Au+Au Au+Au C. Suarez (STAR), poster, QM2008 • Baryon/meson ratios: • “jet”: smaller than inclusive • ridge: similar to inclusive Cu+Cu: C. Nattrass (STAR), QM2008 Au+Au: J.B. (STAR), WWND07 XLIII Rencontres de Moriond

  14. Near-side “jet” and ridge w.r.t. event plane trigger in-plane 3< pTtrig < 4 GeV/c, pTassoc =1.0- 1.5 GeV/c out-of-plane fS=90o in-plane fS=0o Au+Au 200 GeV Au+Au 200 GeV “jet” part, near-side ridge part, near-side jet part, near-side ridge part, near-side 20-60% 0-5% A.Feng (STAR), QM2008 trigger out-of-plane ridge: decreases its magnitude with φS “jet”: slight increase with φS magnitude consistent with d+Au STAR Preliminary STAR Preliminary XLIII Rencontres de Moriond

  15. 3-particle DhxDhcorrelations d+Au Au+Au STAR Preliminary 3<pTtrig<10 GeV/c, 1<pTassoc<3 GeV/c, ||<0.7 2) In medium radiated gluons diffused in  1) Jet fragmentation in vacuum • In medium radiated gluons still collimated Data: STAR Preliminary Uniform overall excess of associated particles observed at intermediate pT (more data needed to look at higher pT) P. Netrakanti (STAR), QM 2008 XLIII Rencontres de Moriond

  16. Summary • Strong modification of correlation patterns (not present in d+Au collisions) observed in central A+A collisions at RHIC: • broadening of away-side peak with angular substructure • inconsistent with Čerenkov gluon radiation • possible evidence for conical emission ? • (need to evaluate effects of momentum conservation) • medium responds through “ridge” formation in pseudo-rapidity • bulk-like properties (spectra, particle composition) • medium density/path length effects (dominated in the event plane) • further studies of 3-particle correlations to understand ridge underway • THANK YOU! XLIII Rencontres de Moriond

  17. BACKUP XLIII Rencontres de Moriond

  18. Centrality and φS dependence: • 20-60% : away-side evolves from single (φS=0o) to double peak (φS=90o) • 0-5% : double peak shows up at smaller φS • at large φS there is little difference between two centrality bins Di-hadron correlations w.r.t. event plane 3< pTtrig < 4 GeV/c, pTassoc=1.0-1.5 GeV/c trigger in-plane out-of-plane fS=90o in-plane fS=0o Au+Au 200 GeV 20-60% STAR Preliminary d+Au d+Au RMS trigger out-of-plane Au+Au 200 GeV STAR Preliminary 0-5% A.Feng (STAR), QM2008 XLIII Rencontres de Moriond

  19. Di-hadron correlations: pathlength effects STAR Preliminary 3< pTtrig < 4 GeV/c, pTassoc=1.0-1.5 GeV/c v2 syst. error Au+Au 200 GeV in-plane: similar to d+Au in 20-60% broader than d+Au in central collisions out-of-plane: small difference between the two centralities v2{EP} v2{4} A.Feng (STAR), QM2008 Away-side features reveal pathlength effects 20-60% 0-5% XLIII Rencontres de Moriond

  20. (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 XLIII Rencontres de Moriond

  21. Armesto et al, PRL 93 (2004) What is the origin of the ridge? (I) 1) Medium heating and parton recombination Chiu & Hwa Phys. Rev. C72:034903,2005 • hard parton enhances thermal parton distribution • (ΔT=15 MeV) •  recombination of thermal partons forms • a pedestal (ridge) • enhanced baryon/meson ratio 2) Parton radiation and its coupling to the longitudinal flow • gluon bremsstrahlung of hard-scattered parton • radiated gluon contributes to broadening Bormio 2008

  22. What is the origin of the ridge? (II) 3) Longitudinal broadening of quenched jets in turbulent color fields • A. Majumder, B. Mueller, S.A.Bass, hep-ph/0611135 • plasma instabilities in expanding medium •  non-thermal color fields • broadening of jet cone • wide ridge in rapidity at low pTassoc Bormio 2008

  23. What is the origin of the ridge? (III) 4) Correlations between jet and radial flow S. Voloshin, nucl-th/0312065, Nucl.Phys. A749, 287 (2005) E. Shuryak, arXiv: 0706.3531 [nucl-th] • radial expansion + jet quenching  correlation • ridge is independent of jet • particle spectra in ridge: • points of origin are biased towards surface •  ‘a bit’ stiffer slope than that of bulk • 5) Momentum kick • C.-Y. Wong , arXiv: 0707.2385, arXiv:0712.3282 • medium partons acquire ‘kick’ from propagating jet • T=470 MeV, q1 (mom. kick) and σy (rapidity distribution) • narrow peak in Dfdepends mainly on momentum kick • ridge in Dh depends on initial parton y distribution More quantitative theoretical predictions are needed! Bormio 2008

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