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Peter Jacobs Lawrence Berkeley National Laboratory

Evidence from d+Au measurements for final-state suppression of high p T hadrons in Au+Au collisions at RHIC The STAR Collaboration. Peter Jacobs Lawrence Berkeley National Laboratory. nucl-ex/0306024. The STAR detector. E-M Calorimeter. Projection           Chamber.

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Peter Jacobs Lawrence Berkeley National Laboratory

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  1. Evidence from d+Au measurements for final-state suppression of high pT hadrons in Au+Au collisions at RHICThe STAR Collaboration Peter Jacobs Lawrence Berkeley National Laboratory nucl-ex/0306024 d+Au and final-state suppression in Au+Au

  2. The STAR detector E-M Calorimeter Projection           Chamber Time of    Flight d+Au and final-state suppression in Au+Au

  3. Partonic energy loss in dense matter Bjorken, Baier, Dokshitzer, Mueller, Pegne, Schiff, Gyulassy, Levai, Vitev, Zhakarov, Wang, Wang, Salgado, Wiedemann,… Multiple soft interactions: Gluon bremsstrahlung Opacity expansion: • Strong dependence of energy loss on gluon density glue: • measure DE color charge density at early hot, dense phase d+Au and final-state suppression in Au+Au

  4. jet parton nucleon nucleon Jets at RHIC Find this……….in this p+p jet+jet (STAR@RHIC) Au+Au ??? (STAR@RHIC) d+Au and final-state suppression in Au+Au

  5. Binary collision scaling p+p reference Partonic energy loss via leading hadrons Energy loss  softening of fragmentation  suppression of leading hadron yield d+Au and final-state suppression in Au+Au

  6. Au+Au and p+p: inclusive charged hadrons nucl-ex/0305015 PhysRevLett 89, 202301 p+p reference spectrum measured at RHIC d+Au and final-state suppression in Au+Au

  7. Suppresion of inclusive hadron yield RAA Au+Au relative to p+p RCP Au+Au central/peripheral nucl-ex/0305015 • central Au+Au collisions: factor ~4-5 suppression • pT>5 GeV/c: suppression ~ independent of pT d+Au and final-state suppression in Au+Au

  8. trigger Jets and two-particle azimuthal distributions p+p  dijet • trigger: highest pT track, pT>4 GeV/c • Df distribution: 2 GeV/c<pT<pTtrigger • normalize to number of triggers Phys Rev Lett 90, 082302 N.B. shifted horizontally by p/2 relative to previous STAR plots! d+Au and final-state suppression in Au+Au

  9. ? Azimuthal distributions in Au+Au Au+Au peripheral Au+Au central pedestal and flow subtracted Phys Rev Lett 90, 082302 Near-side: peripheral and central Au+Au similar to p+p Strong suppression of back-to-back correlations in central Au+Au d+Au and final-state suppression in Au+Au

  10. 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) d+Au and final-state suppression in Au+Au

  11. RCP nucl-ex/0305015 Inclusive suppression: theory vs. data pQCD-I: Wang, nucl-th/0305010 pQCD-II: Vitev and Gyulassy, PRL 89, 252301 Saturation: KLM, Phys Lett B561, 93 Final state Initial state pT>5 GeV/c: well described by KLM saturation model (up to 60% central) and pQCD+jet quenching d+Au and final-state suppression in Au+Au

  12. partonic energy loss Is suppression an initial or final state effect? Initial state? Final state? gluon saturation How to discriminate? Turn off final state d+Au collisions d+Au and final-state suppression in Au+Au

  13. Inclusive spectra RAB If Au+Au suppression is final state 1.1-1.5 1 If Au+Au suppression is initial state (KLM saturation: 0.75) ~2-4 GeV/c pT High pT hadron pairs broadening? pQCD: no suppression, small broadening due to Cronin effect saturation models: suppression due to mono-jet contribution? 0 suppression? /2  0  (radians) d+Au vs. p+p: Theoretical expectations All effects strongest in central d+Au collisions d+Au and final-state suppression in Au+Au

  14. FTPC-Au ZDC-Au ZDC-d Au d d+Au event selection Minimum bias trigger: ZDC-Au (953% of shadronic) Centrality tags: 1. FTPC-Au: charged particle multiplicity in -3.8<h<-2.8 2. ZDC-d: neutron spectator from deuteron d+Au and final-state suppression in Au+Au

  15. Centrality tags • ZDC-d neutron spectator tag: • measured: 191% of shadronic • Glauber: 183% of shadronic •  peripheral events FTPC-Au cut selects more central collisions Modeling FTPC-Au multiplicity: convolute Au-participant (Glauber) with UA5 mult. distribution (pbar+p @ 200 GeV, 2.5<h<3.5) min. bias <Nbinary>=7.00.3; central 20% <Nbinary>=12.91.0 d+Au and final-state suppression in Au+Au

  16. Inclusive charged particle spectra d+Au and final-state suppression in Au+Au

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

  18. pedestal and flow subtracted Azimuthal distributions 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 d+Au and final-state suppression in Au+Au

  19. The strong suppression of the inclusive yield and back-to-back correlations at high pT previously observed in central Au+Au collisions are due to final-state interactions with the dense medium generated in such collisions. d+Au and final-state suppression in Au+Au

  20. 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 This represents significant progress in our understanding of strongly interacting matter 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 ? Not yet, there is still work to do d+Au and final-state suppression in Au+Au We have developed the tools necessary to complete this program

  21. The STAR Collaboration 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. 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 d+Au and final-state suppression in Au+Au

  22. Extra slide d+Au and final-state suppression in Au+Au

  23. 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 d+Au and final-state suppression in Au+Au

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