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 Energy Interactions”

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

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

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 Jana Bielcikova XLIII Rencontres de Moriond

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 40-60% 0-12% Preliminary M. Horner (STAR), J.Phys.G34, S995,2007 To distinguish from other mechanisms 3-particle correlation studies needed Jana Bielcikova XLIII Rencontres de Moriond

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

Conical flow or deflected jets? (II) Bedanga Mohanty STAR uses 2 methods: 1. Jet+flow background - model dependent analysis evidence for conical emission 2. Cumulant method 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 C3  Subtraction of v2v2v4 terms using v2 = 0.06 Subtraction of v2v2v4 term using v2 = 0.12 STAR Preliminary STAR Preliminary 

Mach cone or Čerenkov gluons? Bedanga Mohanty Mach cone or Čerenkov gluons? Cone angle (radians) pT (GeV/c) STAR preliminary Mach cone cone angle independent of pTassoc Čerenkov gluon radiation: cone angle decreases with pTassoc pT dependence of cone angle favors Mach cone over Čerenkov gluon emission Koch, Majumder, Wang, PRL96 172302 (2006) Jana Bielcikova XLIII Rencontres de Moriond

Momentum conservation in correlation analyses C3 cumulant pT conservation 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 Jana Bielcikova XLIII Rencontres de Moriond

A closer look at the near-side peak … pTtrig=3-6 GeV/c, 2 GeV/c <pTassoc< pTtrig d+Au, 200 GeV STAR preliminary Au+Au, 200 GeV “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, PRL 99 (2007) 042301 6) Momentum kick imparted on partons in medium Wong, PRC PRC 76 (2007) 054908 Jana Bielcikova XLIII Rencontres de Moriond

Centrality and system size dependence of near-side yield Bedanga Mohanty  ridge   jet jet+ridge after v2 subtraction “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 Jana Bielcikova XLIII Rencontres de Moriond

“Jet” and ridge: pT dependence STAR preliminary pT assoc > 2 GeV/c Ridge: solid symbols Jet: open symbols J. Putschke (STAR), J.Phys.G34:S679 (2007) J. Putschke (STAR), J.Phys.G34:S679 (2007) STAR preliminary 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 “jet” slope ridge slope inclusive slope h-h correlations pTassociated>2GeV/c Jana Bielcikova XLIII Rencontres de Moriond

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

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

3-particle DhxDh correlations 2) In medium radiated gluons diffused in  1) Jet fragmentation in vacuum In medium radiated gluons still collimated Data: STAR Preliminary d+Au Au+Au 3<pTtrig<10 GeV/c, 1<pTassoc<3 GeV/c, ||<0.7 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 Jana Bielcikova XLIII Rencontres de Moriond

XLIII Rencontres de Moriond 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 Jana Bielcikova

XLIII Rencontres de Moriond BACKUP XLIII Rencontres de Moriond Jana Bielcikova

Di-hadron correlations w.r.t. event plane Bedanga Mohanty Di-hadron correlations w.r.t. event plane trigger in-plane out-of-plane 3< pTtrig < 4 GeV/c, pTassoc=1.0-1.5 GeV/c out-of-plane fS=90o in-plane fS=0o A.Feng (STAR), QM2008 Au+Au 200 GeV STAR Preliminary d+Au 20-60% 0-5% RMS 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 Centrality and φS dependence: XLIII Rencontres de Moriond Jana Bielcikova

Di-hadron correlations: pathlength effects Bedanga Mohanty Di-hadron correlations: pathlength effects 3< pTtrig < 4 GeV/c, pTassoc=1.0-1.5 GeV/c STAR Preliminary v2{4} v2{EP} 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 The RMS increases with phiS. A.Feng (STAR), QM2008 Away-side features reveal pathlength effects 20-60% 0-5% XLIII Rencontres de Moriond Jana Bielcikova

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

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 Armesto et al, PRL 93 (2004) Bormio 2008 Jana Bielcikova

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 Jana Bielcikova

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 Df depends mainly on momentum kick ridge in Dh depends on initial parton y distribution More quantitative theoretical predictions are needed! Bormio 2008 Jana Bielcikova