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Heavy-Ion Collisions at RHIC ~Search for Quark Gluon Plasma~

Heavy-Ion Collisions at RHIC ~Search for Quark Gluon Plasma~. Takao Sakaguchi Brookhaven National Laboratory 米国ブルックヘブン国立研究所 　坂口貴男. Outline of talk Motivation of Quark Gluon Plasma Search Accelerator and detectors Dynamics and Global feature of Heavy ion collisions

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Heavy-Ion Collisions at RHIC ~Search for Quark Gluon Plasma~

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  1. Heavy-Ion Collisions at RHIC~Search for Quark Gluon Plasma~ Takao Sakaguchi Brookhaven National Laboratory 米国ブルックヘブン国立研究所 　坂口貴男 • Outline of talk • Motivation of Quark Gluon Plasma Search • Accelerator and detectors • Dynamics and Global feature of Heavy ion collisions • Hard scattering as a new probe • Direct Photon, Jet and Heavy Quark results • Summary and Future

  2. Why do we carry out Heavy Ion Collisions?Why Quark Gluon Plasma (QGP) ? • Believe it or not! • It existed in the early universe. • Understanding fundamental QCD problem • Quark confinement • Origin of proton (hadron) Mass • Both questions rely on ｌow Q2 region, where as(Q2)>1 • QGP is a phase where bare strong interaction plays significant role • Quarks and gluons are free from hadron “bag” • Study dynamical behavior of strongly interacting system

  3. RHIC at BNL STAR Solenoidal field Large Solid Angle Tracking TPC’s, Si-Vertex Tracking RICH, EM Cal, TOF PHENIX Axial Field High Resolution & Rates 2 Central Arms, 2 Forward Arms TEC, RICH, EM Cal, Si, TOF, -ID BRAHMS 2 Spectrometers - fixed target geometry Magnets, Tracking Chambers, TOF, RICH PHOBOS “Table-top” 2 Arm Spectrometer Magnet, Si -Strips, Si Multiplicity Rings, TOF Paddle Trigger Counter TOF Spectrometer Octagon+Vertex Ring Counters Measurements of Hadronic observables using a large acceptance spectrometer Event-by-event analyses of global observables, hadronic spectra and jets Leptons, Photons, and Hadrons in selected solid angles (especially muons) Simultaneous detection of phase transition phenomena (e–m coincidences) Inclusive particle production over a large rapidity and pt range Low pt charged hadrons Multiplicity in 4 & Particle Correlations Long Island, New York Run started in 2000. Around 6 months running every year. Statistics aka PHENIX experiment. Species s1/2 [GeV ] LdtNtot (sampled)Data Size Au+Au 130 1 mb-1 10M 3 TB Au+Au 200 265mb-11.8G120 TB Au+Au 63 9.1 mb-158M 4 TB p+p 200 0.5 pb-110G 50 TB d+Au 200 2.74 nb-15.5G 46 TB Cu+Cu 200 3.06nb-1 1.1G Cu+Cu 63 0.16 nb-1 • First Heavy Ion collider • 3.83 km circumference • 106 ns bunch crossing • Top Energy: • 500 GeV for p+p • 200 GeV for Au+Au • Luminosity • Au+Au: 2 x 1026 cm-2 s-1 • p+p : 2 x 1032 cm-2 s-1 • (polarized)

  4. Time profile of heavy ion collisions • Gold ions “pass through” each other • Large-x partons fly over. • Mid-rapidity region is full of small-x gluons • High energy heavy ion collisions = Gluonic matter collisions • Turns into Gluon plasma • Gluon -> quark + anti-quark -> QGP • Cooling QGP -> Mixed phase -> Hadronic stage • Global Feature • Energy density: 5.7GeV/fm3 @ Au+Au sNN=200GeV (ref. LQCD: reaches plateau at 2-3GeV/fm3) • Temperature T=178MeV (Threshold) Gluon Plasma QGP phase Mixed phase Hadronization + Expansion

  5. New probe to HEHIC: Hard scattering C P1 x1P1 c X x2P2 P2 d view along beam axis looking from top Centrality 0% (Central) A B Centrality 100% (peripheral)  AB Proportional to number of participated nucleons • Hard scattering process well described by NLO pQCD calculation at high Q2 • Unique Signature at high energy: Hard scattering cross-section is large • Jet and Direct photon • Heavy Quark production: Charm(onium), Bottom(onium) • Cross section in A+B collisions = TAB(b)  p+p collisions • TAB(b): Overlap integral of nuclear profile functions Number of binary collisions • =AB • Can be calculated by Geometrical description of Nucleus In A+B collisions---TAB Scaling

  6. Calibrating Hard scattering Leading Order (LO) Next-to-Leading Order (NLO) PHENIX, nucl-ex/0503003 • High pT Direct photon in Au+Au at sNN=200GeV • Electromagnetic probes bring out information on the stage it is emitted • Direct access to hard scattering (pT>4GeV/c) • Yellow bands show error due to three different cut-off scale of NLO pQCD scaled by number of binary collisions (Ncoll) • NLO pQCD agrees very well with measurement • First measurement of hard scattered direct photon in heavy ion collisions! Hard scattering cross-section in nucleus-nucleus collisions has been calibrated

  7. Jet as a probe of dense medium Parton may change its momentum in hot dense medium Energy loss through Gluon radiation, etc. Reconstruction of Jet in Au+Au is impossible Trigger Leading particle of Jet Angle correlation, Energy, momentum, etc. may reflect Jet kinematics Fragmentation: 0 without energy loss 0 with energy loss Yield [GeV-1c] Energy loss =Yield suppress pT [GeV/c] X.-N., Wang, PRC 58 (1998)2321

  8. High pT Identified hadronspectra(I) 70-80% Centrality (peripheral) 0-10% Centrality (Central) pT [GeV/c] • Produced in initial hard scattering process • Should scale with Ncoll if no additional process exists • In peripheral Au+Au collisions, yield is consistent with p+p collisions scaled by Ncoll • In Central Au+Au collisions, yield is significantly lower than p+p • Energy loss of hard scattered parton in hot and dense medium? pT [GeV/c] sNN=200GeV PHENIX, PRL91, 072301 (2003)

  9. High pT Identified hadronspectra(II) d+Au Minimum bias Au+Au Peripheral 200 GeV 0 RAA /RdA Au+Au Central • Nuclear Modification Factor: RAA • Ratio of per-collision-yield to p+p • Hard scattering only: ratio is 1 • Peripheral Au+Au, Minimum bias d+Au: = 1 • Central Au+Au: << 1 • Is suppression due to final state interaction? • Au+Au Direct photon: RAA= 1 • Suppression is final state effect • Energy loss of parton in hot dense medium • Medium expands in longitudinal direction as well? • Suppression at high rapidity region • Answer is Yes! BRAHMS, PRL91, 072305 (2003) PHENIX, PRL91, 072301 (2003) PHENIX, PRL91, 072303 (2003)

  10. Modification of away side Jet near Trigger particles sit at 0. away Au + Au peripheral away Collimatedregion Au + Au central Histogram: p+p, Black Points: Au+Au Blue Line: Mixed background • Correlation of back-to-back jets through high pT hadrons • Trigger leading high pT (4<pT<6) hadrons • Angle correlation of lower pT (2<pT<trig) particles with triggered hadrons • Near side: In Same Cone of leading • Away side: In Cone of associated jet • p+p and peripheral Au+Au: • Near side yield = Away side yield • Central Au+Au: away side particles suppressed. • Energy loss of away side Jet • Near side jet produced almost at surface of medium STAR PRL90, 082302 (2003)

  11. Where is away side Jet ? Near(Trigger) Side Away Side Wake effect or “sonic boom” hep-ph/0411315 Casalderrey-Solana,Shuryak,Teaney Correlations of Jets with flowing medium hep-ph/0411341 Armesto,Salgado,Wiedemann (Folded into 0-p ) Interpretation.. W. Holtzmann for PHENIX, WWND, 2005 Even lower pT associated particles (1.0<pT<2.5) Strong Modification of away-side Jet observed! Dawn of Jet tomography

  12. Heavy Quark(onium) D mesons , Y’, c • Charm or bottom produced in hard scattering process • Energy loss of light quark is mostly due to gluon radiation (analogous to Bremsstrahlung) • How about heavier quarks? Collisional energy loss? • Charmonium in hot dense medium will be: • Suppressed due todissociation (debye screening) • Enhanced due to coalescence of c-cbar Large Q value needed (>≈3GeV) pQCD should work better! J/ (M=3.1GeV/c2)

  13. Single heavy quark measurement Phys. Rev. Lett. 88, 192303 (2002) • Experimentally observe the decay products of Heavy Flavor particles (e.g. D-mesons) • Hadronic decay channels DKp, D0p+ p- p0 • Semi-leptonic decays De(m) K ne • STAR • Direct D mesons hadronic decay channels in d+Au • D0Kp • D±Kpp • D*±D0p • Single electron measurements in p+p, d+Au • PHENIX • Single electron measurements in p+p, d+Au, Au+Au sNN = 130,200,62.4 GeV

  14. Single electron Result • Strong modification of the spectral shape in Au+Au is observed at high pT • Statistics insufficient to quantify centrality dependence • Possibility of different energy loss mechanism? RAA of Integrated CS (2.5<pT<5.0 GeV/c). PHENIX PRELIMINARY T. Tabaru for PHENIX, ICPAQGP05, 2005

  15. Where is suppressed Charm? dN/d=v0/(2)+v2cos(2) /+… • Particles boosted by pressure gradients in collision area • Elliptic shape turns into anisotropic flow • Positive flow(v2) = Collective motion with expanding system = Hint of equilibrium • Energy loss of charm implies interaction of charm with the medium • Charm participate in collective motion! Strong indication of “quark level” early equilibrium STAR, nucl-ex/0411007, Theory curves from:Greco, Ko, Rapp: Phys. Lett. B595 (2004) 202

  16. Charmonium results Phys.Rev.C69, 014901,2004 R. L. Thews, M. Schroedter, J. Rafelski, Phys Rev C 63, 054905 Plasma Coalescence Model J/->ee Au+Au sNN=200GeV y = 1.0 Binary Scaling Stat.Model Andronic et al nucl-th/0303036 y = 4.0 Absorption (Nuclear + QGP) + final-state coalescence Absorption (Nuclear + QGP) L. Grandchamp, R. Rapp, Nucl Phys A709, 415; Phys Lett B 523, 60 First J/ ->ee measurement in heavy ion collisions! Not enough statistics to make definitive conclusions

  17. Summary • Hard scattering (pQCD) as new probe for NpQCD QGP • Cross section is significantly large at RHIC. Calculable by pQCD • Calibrated by Direct photon • First measurement in high energy heavy ion collisions • Jet modification • High pT particle yield (fragment of Jet) suppression in central Au+Au collisions • Hot dense medium expanding both transverse and longitudinal direction • Away side jet is strongly modified • Hint of Charm suppression and flow in Au+Au collisions • Needs more statistics to conclude • High Statistics Run4 Au+Au data is now in analysis • 10 times statistics: ~ 1.5G events accumulated • Thermal radiation on top of pQCD photon -> Direct emission from QGP • 700 J/y’s expected -> precise measurement of charmonium • Complemented by Run5 Cu+Cu data on system size dependence • Hard scattering will be even more powerful probe at LHC Future Outlook

  18. RHIC Collaborations STAR

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