STAR HIC031 Jets and high p T hadrons at RHIC: recent results from STAR Peter Jacobs Lawrence Berkeley National Laboratory Inclusive spectra Single-particle azimuthal asymmetry (“elliptic flow”) Two-particle azimuthal distributions Results from the d+Au run What have we learned at RHIC?

STAR HIC032 E-M Calorimeter Time of Flight Projection Chamber The STAR detector

STAR HIC033 Partonic energy loss in dense matter Multiple soft interactions: Strong dependence of energy loss on gluon density  glue  measure   color charge density at early hot, dense phase Gluon bremsstrahlung Opacity expansion: Bjorken, Baier, Dokshitzer, Mueller, Pegne, Schiff, Gyulassy, Levai, Vitev, Zhakarov, Wang, Wang, Salgado, Wiedemann,…

STAR HIC034 Jets at RHIC p+p  jet+jet Au+Au  ??? nucleon parton jet Find this……….in this

STAR HIC035 Partonic energy loss via leading hadrons - Energy loss  softening of fragmentation  suppression of leading hadron yield Binary collision scalingp+p reference

STAR HIC036 Au+Au and p+p: inclusive charged hadrons PhysRevLett 89, nucl-ex/ p+p reference spectrum measured at RHIC

STAR HIC037 Suppresion of inclusive hadron yield central Au+Au collisions: factor ~4-5 suppression p T >5 GeV/c: suppression ~ independent of p T nucl-ex/ Au+Au relative to p+p Au+Au central/peripheral R AA R CP

STAR HIC038 Azimuthal anisotropy wrt reaction plane (“Elliptic Flow”) Coordinate space: initial asymmetry Momentum space: final asymmetry asymmetry generated early in collision, quenched by expansion  observed asymmetry emphasizes early time Second Fourier coefficient v 2 : multiple collisions (pressure) pypy pxpx

STAR HIC039 Azimuthal anisotropy at high p T : theory Snellings; Gyulassy, Vitev and Wang (Phys Rev Lett 2537 (2001) ) Jet propagation through anisotropic matter (non-central collisions) Finite v 2 : high p T hadron correlated with reaction plane from “soft” part of event (p T <2 GeV/c) jet

STAR HIC0310 Azimuthal anisotropy at high p T : dataSTAR p T <2 GeV: detailed agreement with hydrodynamics p T >4 GeV: finite v 2 in qualitative agreement with expectations from partonic energy loss STAR preliminary Phys Rev Lett 90,

STAR HIC0311 Jets and two-particle azimuthal distributions p+p  dijet trigger: highest p T track, p T >4 GeV/c  distribution: 2 GeV/c<p T <p T trigger normalize to number of triggers trigger N.B. shifted horizontally by  /2 relative to previous STAR plots! Phys Rev Lett 90,

STAR HIC0312 Azimuthal distributions in Au+Au Au+Au peripheral Au+Au central Near-side: peripheral and central Au+Au similar to p+p Strong suppression of back-to-back correlations in central Au+Au collisions pedestal and flow subtracted Phys Rev Lett 90,

STAR HIC0313 What might all this mean? ? Conjecture: core of reaction volume is opaque to jets  surface emission Consequences: near-side fragmentation independent of system suppression of back-to-back jets suppression of inclusive rates strong elliptic flow at high p T Compelling picture, but is it right?

STAR HIC0314 Is suppression an initial or final state effect? Initial state?Final state? partonic energy loss in dense medium generated in collision strong modification of Au wavefunction (gluon saturation at low Bjorken x?)

STAR HIC0315 nucl-ex/ R CP Inclusive suppression: theory vs. data pQCD-I: Wang, nucl-th/ pQCD-II: Vitev and Gyulassy, PRL 89, Saturation: KLM, Phys Lett B561, 93 p T >5 GeV/c: well described by KLM saturation model (up to 60% central) and pQCD+jet quenching Final state Initial state

STAR HIC0316 Is suppression an initial or final state effect? Initial state? gluon saturation Final state? partonic energy loss How to discriminate? Turn off final state  d+Au collisions

STAR HIC0317 d+Au vs. p+p: Theoretical expectations If Au+Au suppression is initial state (KLM saturation: 0.75) pTpT R AB 1 Inclusive spectra If Au+Au suppression is final state ~2-4 GeV/c All effects strongest in central d+Au collisions pQCD: no suppression, small broadening due to Cronin effect 0  /2   (radians) 0 High p T hadron pairs saturation models: suppression due to mono-jet contribution? suppression? broadening?

STAR HIC0318 ZDC-d FTPC-Au Au d ZDC-Au d+Au event selection Centrality tags: 1. FTPC-Au: charged particle multiplicity in -3.8<  < ZDC-d: neutron spectator from deuteron Minimum bias trigger: ZDC-Au (95  3% of  hadronic )

STAR HIC0319 Centrality tags FTPC-Au cut selects more central collisions Modeling FTPC-Au multiplicity: convolute Au-participant (Glauber) with UA5 mult. distribution 200 GeV, 2.5<  <3.5) min. bias =  central 20% =12.9  1.0 ZDC-d neutron spectator tag: measured: 19  1% of  hadronic Glauber: 18  3% of  hadronic  peripheral events

STAR HIC0320 Inclusive charged particle spectra

STAR HIC0321 Inclusive yield relative to binary-scaled p+p Suppression of the inclusive yield in central Au+Au is a final-state effect d+Au : enhancement Au+Au: strong suppression p T =4 GeV/c: cent/minbias = 1.11  0.03  central collisions enhanced wrt minbias

STAR HIC0322 Azimuthal distributions pedestal and flow subtracted Near-side: p+p, d+Au, Au+Au similar Back-to-back: Au+Au strongly suppressed relative to p+p and d+Au Suppression of the back-to-back correlation in central Au+Au is a final-state effect

STAR HIC0323 The strong suppression of the inclusive yield and back-to-back correlations at high p T previously observed in central Au+Au collisions are due to final-state interactions with the dense medium generated in such collisions. ? X STAR collaboration, nucl-ex/ :

STAR HIC0324 Have we found the Quark Gluon Plasma at RHIC? We now know that Au+Au collisions generate a medium that is dense (pQCD theory: many times cold nuclear matter density) is dissipative exhibits strong collective behavior Not yet, there is still work to do We have yet to show that: dissipation and collective behavior both occur at the partonic stage the system is deconfined and thermalized a transition occurs: can we turn the effects off ? We have developed the tools necessary to complete this program This represents significant progress in our understanding of strongly interacting matter

STAR HIC0325 Russia: MEPHI - Moscow LPP/LHE JINR - Dubna IHEP - Protvino U.S. Laboratories: Argonne Berkeley Brookhaven U.S. Universities: UC Berkeley UC Davis UC Los Angeles Carnegie Mellon Creighton University Indiana University Kent State University Michigan State University City College of New York Ohio State University Penn. State University Purdue University Rice University Texas A&M UT Austin U. of Washington Wayne State University Yale University Brazil: Universidade de Sao Paulo China: IHEP – Beijing IMP - Lanzou IPP – Wuhan USTC SINR – Shanghai Tsinghua University Great Britain: University of Birmingham France: IReS Strasbourg SUBATECH - Nantes Germany: MPI – Munich University of Frankfurt India: IOP - Bhubaneswar VECC - Calcutta Panjab University University of Rajasthan Jammu University IIT - Bombay VECC – Kolcata Poland: Warsaw University of Tech. The STAR Collaboration

STAR HIC0326 Extra slides

STAR HIC GeV Au+Au:  and K 0 s STAR preliminary K0sK0s Power-law shape except for central  STAR preliminary  bar

STAR HIC0328 Central/peripheral: dependence on particle species STAR preliminary 1.5<p T <3.5 GeV/c:  scales ~N binary, K 0 s suppressed p T ~ 6 GeV/c: , K 0 s, charged hadrons scale similarly “baryon enhancement”: partonic flow? modified fragmentation? Cronin effect? …

STAR HIC0329 Important complication: non-flow STAR Preliminary Non-flow: any two-particle correlation not due to correlation with the reaction plane: jets, resonances, momentum conservation, …. Borghini, Ollitraut et al: measure non-flow via higher order correlations (cumulants) Non-flow Finite flow at p T ~7 GeV/c

STAR HIC0330 Two-particle azimuthal distributions near-side and back-to-back peaks seen in minbias and central d+Au p+p  d+Au minbias  d+Au central: growth of off-jet pedestal small, if any, growth of back-to-back width

STAR HIC0331 Near-side correlations II  < 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… Phys. Rev. Lett. 90, (2003)

STAR HIC0332 Reality check: charge-sign dependence |  | 0.5 (scaled) 0<|  |<1.4 Au+Au p+p System(+-)/(++ & --) p+p % Au+Au Jetset DELPHI, PL B407, 174 (1997) Compare same-sign (++, --) and opposite-sign (+-) pairs Known jet physics: charge ordering in fragmentation Opposite/same correlation strength similar in Au+Au, p+p, JETSET  p T ~3-4 GeV are jet fragments STAR preliminary