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Evidence for a new phase of matter measured with the STAR experiment at RHIC

Evidence for a new phase of matter measured with the STAR experiment at RHIC. Rene Bellwied Wayne State University. International Nuclear Physics Conference Goteborg, Sweden, June 27- July 2, 2004. The compelling global questions.

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Evidence for a new phase of matter measured with the STAR experiment at RHIC

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  1. Evidence for a new phase of matter measured with the STAR experiment at RHIC Rene Bellwied Wayne State University International Nuclear Physics Conference Goteborg, Sweden, June 27- July 2, 2004

  2. The compelling global questions Is there evidence for a phase transition to a deconfined and chirally symmetric phase of quarks and gluons at high T ? Is this phase thermally and chemically equilibrated ? Are the quarks and gluons weakly interacting, as expected from a plasma, or strongly interacting as expected from an ideal fluid description ? Could there be evidence for a different phase of matter at even lower x ?

  3. Different types of RHIC measurements(producing probe and medium in the same collision) • We are producing ‘soft’ and ‘hard’ matter. An arbitrary distinction is coming from the applicability of pQCD which is generally set to pT > 2 GeV/c (hard). Below 2 GeV/c we expect thermal bulk matter production. • Medium: The bulk of the particles; dominantly soft production and possibly exhibiting some phase. • Probe: Particles whose production is calculable, measurable, and thermally incompatible with (distinct from) the medium (hard production) • Measure bulk matter properties to determine global properties (collectivity, equilibration, timescales) • Measure the modification of high pt probes to determine specific properties of the matter produced

  4. Behavior of hard probes when traversing an opaque medium Jets from hard scattered quarks observed via fast leading particles or azimuthal correlations between the leading particles • However, before they create jets, the scattered quarks radiate energy (~ GeV/fm) in the colored medium: • decreases their momentum (fewer high pT particles) • “kills” jet partner on other side

  5. 99.5% Understanding ‘bulk properties’ Dominant feature: order of magnitude increase at high pT

  6. Directed flow Elliptic flow Elliptic(anisotropic)Flowfor a mid-peripheral collision– a strong indicator of collectivity Flow Y Out-of-plane In-plane Reaction plane Flow X Dashed lines: hard sphere radii of nuclei Re-interactions  FLOW Re-interactions of hadrons or partons or both ?

  7. PHOBOS: Phys. Rev. Lett. 89, 222301 (2002) STAR: Phys. Rev. Lett. 86, 402 (2001) Hydrodynamic limit STAR PHOBOS RQMD Figure from Masashi Kaneta (BNL) v2 (anisotropy, squeeze-out) measurements First time in Heavy-Ion Collisions a system created which, at low pt ,is in quantitative agreement with ideal hydrodynamic model predictions for v2 up to mid-central collisions

  8. Y Time X System deformation confirmed in HBT • Final state eccentricity from • v2 • HBT with respect to reaction plane • Conclusions: • System was still deformed at freezeout • System froze out EARLY Time

  9. Elliptic flow v2 scaling at intermediate to high-pt • two groups, baryons and mesons • suggesting relevance of constituent quarks in hadron production • Further tests: f, r0, K*, pentaquarks • scaling could be seen as a signature of deconfinement ! S.A. Voloshin, Nucl. Phys. A715, 379 (2003).D. Molnar and S.A. Voloshin, PRL 91, 092301(2003).

  10. Another sign of deconfinement: energy and particle production at RHIC dNg/dy ~ 200 (HIJING) dNg/dy ~ 1000 (CGC) Gluon density in proper model Equals final state hadron density: dNch/dy ~ 1000 (measured) Parton – hadron duality ??

  11. BRAHMS: 10% central PHOBOS: 10% PHENIX: 5% STAR: 5% Radial expansion: Identified particle spectra in Au-Au • The spectral shape gives us: • Kinetic freeze-out temperatures • Transverse flow • The stronger the flow the less appropriate are simple exponential fits: • Hydrodynamic models (e.g. Heinz et al., Shuryak et al.) • Hydro-like parameters (Blastwave) • Blastwave parameterization e.g.: • Ref. : E.Schnedermann et al, PRC48 (1993) 2462 • Hydromodels Yield common freeze out T & radial expansion velocity b

  12. Tdec = 100 MeV Kolb and Rapp,PRC 67 (2003) 044903. , STAR preliminary ,K,P, Blastwave vs. Hydrodynamics If blastwave is correct this might be an indication for early development of radial flow i.e. collectivity at the partonic level

  13. Electrons from TPC,TOF & EMC STAR Preliminary Charm Beauty The Ultimate test of parton collectivity: D-meson expansion • D0, D, D* spectra from d+Au • Cover range 0.2 < pT < 11 GeV/c • Necessary baseline for Au+Au

  14. Particle production ‘chemistry’: beautiful agreement with statistical chemical equilibration model for non-resonant particles

  15. Does the thermal model always work ? Data – Fit (s) Ratio • Resonance ratios not well described  Reaction dynamics

  16. Strange resonances in medium Short life time [fm/c] K* < *< (1520) <  4 < 6 < 13 < 40 Rescattering vs. Regeneration ? Medium effects on resonance and their decay products before (inelastic) and after chemical freeze out (elastic). Red: before chemical freeze out Blue: after chemical freeze out

  17. Life time: K(892) = 4 fm/c L(1520) = 13 fm/c • Model includes: • Temperature at chemical freeze-out • Lifetime between chemical and • thermal freeze-out • By comparing two particle ratios • (no regeneration) • results between : • T= 160 MeV => •  > 4 fm/c(lower limit !!!) • in agreement with T and dt from • Stable particle analysis G. Torrieri and J. Rafelski, Phys. Lett. B509 (2001) 239 Lifetime and centrality dependence from (1520) / and K(892)/K

  18. hadronic phase and freeze-out QGP and hydrodynamic expansion initial state Balance function (require flow) pre-equilibrium Resonance survival hadronization Rout, Rside Rlong (and HBT wrt reaction plane) dN/dt time 5 fm/c 1 fm/c 10 fm/c 20 fm/c Chemical freeze out Kinetic freeze out Time scales according to STAR data

  19. How to test the matter with high pt probes Is jet quenching an initial or final state effect ?

  20. ? We measure two predicted ‘QGP signatures’ • The ‘quenching’ of high pt particles due to radiative partonic energy loss • The disappearance of the away-side jet in dijet events traversing the apparently opaque medium

  21. Initial state? Final state? Is suppression of high pt particles in RHIC AA collisions an initial state (due to gluon saturation) or final state (due to jet quenching) effect? strong modification of Au wavefunction (gluon saturation) partonic energy loss in dense medium generated in collision Ultimate test: dA collisions

  22. Striking difference of d+Au and Au+Au results. Enhancement vs. suppression. (Cronin effect in cold nuclear matter). Final state effect confirmed by back-to-back correlations Energy loss depends on the size of medium traversed Pedestal&flow subtracted Cronin Effect: Multiple Collisions broaden high PT spectrum Nuclear suppression factors(AA/pp) vs (dA/pp)

  23. RCP Hadron suppression prevails at 62 GeV • 2 h bins, driven by p+p • h = 0: pT <~6 GeV • h = 0.7: pT <~10 GeV • Significant suppression seen at 62 and 200 GeV • 1/3 of dataset: quantitative treatment awaits full analysis

  24. STAR Preliminary p+p pTrigger = 4 -6GeV/c (1/Ntrig) dN/d(Df) syst. error Leading hadrons stat. mom. conserv.Borghini et al. Df STAR Preliminary Au+Au 5% Near Away Medium (1/Ntrig) dN/d(Df) stat. mom. conserv.Borghini et al. Df Where does the energy go? • On the away side: energy loss in medium has been converted to lower pt particles <pt> in cone is still higher than in medium but is approaching equilibration with medium • Statistical distribution of momentum conservation describes the correlation function at all centralities

  25. Identified particles at intermediate to high-pt • Two groups, baryons and mesons, which seem to approach each other around 5 GeV/c • Suggesting relevance of constituent quarks for hadron production • Coalescence/recombination provides a description ~1.5 - 5 GeV/c

  26. Recombination + Fragmentation at mid pt Recombination at moderate PT Parton pt shifts to higher hadron pt. Fragmentation at high PT: Parton pt shifts to lower hadron pT Recomb. fragmenting parton: ph = z p, z<1 recombining partons: p1+p2=ph Frag.

  27. (nucl-th/0403032) Summary of experimental observations • At RHIC we showed that Au+Au collisions create a medium that is dense, dissipative and exhibits strong collective behavior • We observe suppression phenomena in single particle observables and very importantly also in the correlations (large acceptance) • We observe constituent quark scaling in v2 and Rcp at ~ 2-5 GeV/c and gluon density scaling in the energy production • We observe strong collective behavior (flow) in all bulk matter observables

  28. Maximum opacity (Gyulassy 01) Navier-Stokes (Teaney 03) A few thoughts for your way home The matter produced is an almost perfect fluid ! A strongly interacting parton liquid is not what we expected. (sQGP is the new theory label)

  29. Shuryak, QM04 Cassing, priv.comm. parton fluid (pre-hadrons) deconfinement c restoration Where is the weakly interacting plasma ?

  30. STAR: 51 Institutions, ~ 500 People U.S. Labs: Argonne, Lawrence Berkeley, and Brookhaven National Labs U.S. Universities: UC Berkeley, UC Davis, UCLA, Caltech, Carnegie Mellon, Creighton, Indiana, Kent State, MIT, MSU, CCNY, Ohio State, Penn State, Purdue, Rice, Texas A&M, UT Austin, Washington, Wayne State, Valparaiso, Yale Brazil: Universidade de Sao Paolo China: IHEP - Beijing, IPP - Wuhan, USTC, Tsinghua, SINR, IMP Lanzhou Croatia: Zagreb University Czech Republic: Nuclear Physics Institute England: University of Birmingham France: Institut de Recherches Subatomiques Strasbourg, SUBATECH - Nantes Germany: Max Planck Institute – Munich University of Frankfurt India: Bhubaneswar, Jammu, IIT-Mumbai, Panjab, Rajasthan, VECC Netherlands: NIKHEF Poland: Warsaw University of Technology Russia: MEPHI – Moscow, LPP/LHE JINR – Dubna, IHEP – Protvino Switzerland: University of Bern

  31. Consequences of a strong v2 and final state jet quenching at RHIC 1.) v2 is strong and has to come from very early time after collision. Hadronic v2 is not sufficient in terms of magnitude and timescale 2.) v2 is very well described by hydrodynamics (fluid dynamics). 3.) if the phase producing the flow is partonic then we have partonic fluid (dissipative, strongly interacting, small correlation length) rather than a plasma (large correlation length, weakly interacting quasi-particle gas).

  32. Discovery of the suppression phenomena at RHIC • The observed strong suppression can be described efficiently by parton energy loss in matter starting with large energy and gluon densities • Does the magnitude of parton energy loss inferred from these observations demand an explanation in terms of traversal through deconfined matter? • Can we prove from the inferred densities that deconfined matter has been created?

  33. Is the system in approximate local thermal equilibrium? • The unprecedented success of hydrodynamics calculations assuming ideal relativistic fluid behavior in accounting for RHIC elliptic flow results has been interpreted as evidence for both early attainment of local thermal equilibrium and softening of the equation of state, characteristic of the predicted phase transition. • How do we know that the observed elliptic flow can not result alternatively from a harder EOS coupled with incomplete thermalization? (D. Teaney, J. Lauret, E.V. Shuryak; Phys. Rev. Lett 86, 4783 (2001))

  34. BRAHMS, R. Debbe (DNP2003) BRAHMS, R. Debbe (DNP2003) Saturation at low x (10-3)? LHC ions saturated (ycm)? LHC ycm ? RHIC forward? RHIC in unique region! ycm  final state effects forward  initial state RHIC ycm Physics at RHIC II in an LHC-era Nuclear modifications in dAu at h = 3.2!

  35. p0 “Mono-jet” PT is balanced by many gluons Dilute parton system (deuteron) p0 Beam View Top View • Ep > 25 GeV •   4 Dense gluon field (Au) Large Dhp0+h± correlations f • Suppressed at small <xF> , <pT,p> • Consistent with CGC picture • Consistent in d+Au and p+p at larger <xF> and <pT,p> • as expected by HIJING 25<Ep<35GeV STAR Preliminary Fixed h, as E & pT grows 35<Ep<45GeV Statistical errors only dAu Correlations: probing low x

  36. The QGP is almost a perfect fluid Gluon transport: molnar,gyuallasy (01) navier-stokes: teaney (03) opacity

  37. V2 in Au+Au 62GeV

  38. Momentum conservation

  39. Strangeness Enhancement Resonances Particle yields • Chemical freeze-out 160 +/- 10 MeV, close to expected critical temperature, particle ratios similar in pp for most abundant species • Deviations of the resonance yields compared to thermal model predictions indicative of hadronic phase after chemical freeze-out STAR O PHENIX

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