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Recent RHIC Results Spencer Klein, LBNL SLAC Orange Room Seminar , Sept. 19, 2006

Recent RHIC Results Spencer Klein, LBNL SLAC Orange Room Seminar , Sept. 19, 2006. RHIC Collider & Detectors Other Physics photoproduction & polarized protons Cold nuclear matter: pp/dA Hot nuclear matter: AA Future Plans Conclusions. RHIC has published ~ 200 papers

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Recent RHIC Results Spencer Klein, LBNL SLAC Orange Room Seminar , Sept. 19, 2006

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  1. Recent RHIC Results Spencer Klein, LBNLSLAC Orange Room Seminar, Sept. 19, 2006 RHIC Collider & Detectors Other Physics photoproduction & polarized protons Cold nuclear matter: pp/dA Hot nuclear matter: AA Future Plans Conclusions RHIC has published ~ 200 papers I can only hit the biggest highlights

  2. RHIC • RHIC was built to explore the properties of nuclear matter under extreme conditions • Polarized parton distributions • Cold nuclear matter - nuclei • Hot nuclear matter – the QGP? • Study ‘typical’ collisions, not rare events.

  3. BRAHMS/ pp2pp PHOBOS PHENIX STAR h The Relativistic Heavy Ion Collider • 2 concentric rings of 1740 superconducting magnets • 3.8 km circumference • counter-rotating beams of ions from p to Au Brookhaven National Laboratory

  4. RHIC datasets from Au to p • System size scan • AuAu & CuCu • Collision energy scan • 200, 130, 62, 22 GeV per nucleon • dAu • pp • Polarization up to 65%

  5. PHENIX: 2 arm spectrometer Good PID for rare probes STAR: full acceptance Detector for global event reconstruction pp2pp: elastic scattering PHOBOS: full acceptance BRAHMS: 2 precision spectrometers

  6. ‘Other’ Physics • Polarized Protons and polarized parton distributions • Photoproduction • Search for strangelets in AuAu collisions

  7. Polarized parton studies Longitudinal Asymmetry PHENIX, 2006 • Quark, gluon polarization • Compare cross sections for proton polarizations in the same vs. in opposite directions • Longitudinally and transversely polarized beams • Many different structure functions ALL

  8. Au g r, r*, J/y Au “Pomeron Photonuclear and two-photon interactions at RHIC • Ions support a large Weizsäcker-Williams photon flux • Photon flux ~ Z2 • Copious photonuclear interactions • Coherent vector meson production has a large cross section • RHIC has studied r0, r*0 and J/y photoproduction in AuAu, r0 in dA • RHIC has studied ‘two-photon’ production of e+e- • Rate ~ Z4 • The LHC is the only place to study photoproduction at energies above HERA PHENIX J/y Mee (GeV)

  9. 0.1 < |y| < 0.5 Data (w/ fit) MC – no Interference MC - interference dN/dt STAR Preliminary t ~ pT2 (GeV2) Unique Reactions - • Can’t tell if nucleus 1 or nucleus 2 emitted the photon • 2-source interferometer • Negative parity --> subtract amplitudes • ‘+’ sign at pp colliders • s ~ |A1- A2eip·b|2 • At y=0 s=s0[1 - cos(pb)] • Large Z --> multiple reactions • Au + Au --> Au* + Au* + r0 • 3 & 4 photon exchange

  10. pp, dA and cold nuclear matter • pp collisions • tests of pQCD calculations • dA collisions • Use deuteron to probe gold nucleus • Cold nuclear matter • Parton distributions at low Feynman-x • Benchmark for studies of ion-ion collisions

  11. Inclusive jets Hadron production at large pT: data vs. QCD ds/dpT (mb/GeV) p0 (Data-theory)/theory Jet pT pp collisions & pQCD • Jet cross sections and high pT particle spectra are both well fit by pQCD + fragmentation functions • Thanks to recent theoretical advances (Data-theory)/theory p0pT

  12. Decreasing x --> dAu collisions Decreasing Q2 --> • Gluon density rises as x decreases and/or Q2 increases • At high densities gluons overlap & densities saturate • Saturation occurs at larger x in nuclei • Shadowing’ – reduced parton densities in ions, compared to nucleons • Many theoretical approaches • Evolution equations(BFKL/DGLAP) • Colored Glass Condensate – describe gluons with a classical field

  13. BRAHMS Particle Production at Forward x Increasing Rapidity (decreasing x)---> s(dA)/s(pp) Forward Central BRAHMS, PRL 93, 242303 s(central dA)/ s(peripheral dA) Sizable suppression in charged hadron production in d+Au collisions relative to p+p collisions at forward rapidity

  14. jet g g jet Is this a Colored Glass Condensate? • Suppression curves may be fit by multiple models • x=10-2 -10-3 is moderate, not small • In lowest order pQCD g + g --> g + g (or q + q) produces back-to-back jets • Moderate higher order corrections • In a CGC, the target reacts coherently • g + target --> g + target • Heavy target absorbs the impact with little recoil • ‘Monojets’ pQCD jet g CGC No jet Colored Glass Condensate

  15. STAR Forward p0 trigger 2 particle correlations Df =fp – fh Mid-rapidity h± • Azimuthal (f) angle correlations between forward p0 and central h± correlations in pp and dAu • If a CGC is present in Au, correlation should be smaller in dA • Correlations smaller in dA than pp • More suppression at small pT --> smaller x • Consistent with CGC nucl-ex/0602011 Df =fp – fh π0:|<η>| = 4.0 h±: |η| < 0.75; pT > 0.5 GeV/c

  16. Heavy ion collisions and hot nuclear matter • Hot nuclear matter is produced by colliding heavy ions • Study the properties of hot nuclear matter • Search for the Quark Gluon Plasma • Interacting quarks and gluons, in equilibrium • Individual nucleons disappear or Normal Nucleus protons + neutrons Quark Gluon Plasma quarks+ gluons

  17. Nuclear matter phase diagram Plasma Phase boundaries calculated with lattice QCD Transition temperatureTc ~ 170 MeV at zero baryon density At low baryon densities, no phase transition expected – gradual change At higher baryon densities, 2nd order phase change may be present

  18. Space-Time evolution Outgoing baryons Thermal freezeout: elastic scattering stops Global characteristics Particle Spectra Elliptic Flow HBT Central Region Chemical freezeout: inelastic scattering stops Chemical Composition Initial Collisions: hard probes produced high pT particles charm

  19. Observables in ion collisions • Impact parameter (b) and centrality • Npart and Nbin • System composition and thermal equilibrium • Expanding fireball (blast wave) model • Nuclear flow & hydrodynamics • System size – quantum (HBT) interferometry • High pT particles and nuclear energy loss • Particle Correlations • J/y suppression

  20. b=0 Npart=2A Nbin ~ A2 Impact parameter and centrality determination b ~ RA spectators • Impact parameter (b) is not directly observable • Charged particle multiplicity or ET • Spectator neutrons • Common variables • Npart – number of nucleons involved in collision • Nbin – number of nucleon-nucleon collisions • Important for hard probes • %age of collision • e.g. 0-10% most central ds/dNh- Log scale! Nh-

  21. =1 =2 =0 =6.3  =-6.3 PHOBOS Charged particle Distributions • Pseudorapidity h related to longitudinal velocity • Neglecting particle mass • Rapidity plateau dN/d ~ constant for | | <2 • Boost invariance • Radial expansion • dN/d scales with Npart • Independent of incident nuclei • Total charged multiplicity in central AuAu collisions is 4200 +/- 470 dN/d @ 200 GeV Au+Au 35-40%, Npart = 99 dNch/dh Cu+Cu Preliminary 3-6%, Npart = 100 h PHOBOS

  22. short lived resonances Particle Ratios Flavor Composition • Particles of different mass, etc. are in in thermal equilibrium • N ~ exp(-m/kT) • Strangeness fully equilibrated • Suppression gs rises with Npart • Particles are produced individually, rather than as ss pairs • ‘Bath’ conserves strangeness • ‘Grand canonical ensemble • Possible exception – short-lived resonances e.,g L*, K* • Tch ≈ TC ≈ 165 ± 10 MeV Points – data Lines – thermal model gs – strangeness suppression gs Npart

  23. “Blast wave” model -explosive expansion • System is a fireball collective (hydrodynamic) expansion • Particle <pT> rises with particle mass • Main parameters are fit from particle spectra • Temperature T ~ 106 MeV • Expansion velocity <b> ~ 0.55 c • Different velocity profiles can be used pT (GeV/c) Retiere & Lisa, 2003

  24. PHENIX data Baryon enhancementat moderate pT p/p ratio • For 1 < pT < ~ 5 GeV, baryon production is enhanced over pp/dA… • Not a mass effect - f behaves ‘normally’ • Not consistent with usual fragmentation picture • One model – recombination among already produced quarks pT (GeV/c) pT (GeV/c) pT (GeV/c) Rainer Fries

  25. Elliptic flow f • Pressure converts initial state spatial asymmetries into density/momentum asymmetries • Occurs very early in collision • dN/df ~ 1+2v2 cos(2f) + … • Directed flow - v1cos(f) ignored • Small v4cos(4f) ignored • v2 ~ pT for pT < 2.5 GeV • v2 is at hydrodynamic limits • Spatial anisotropy is completely converted into particle asymmetry • Hot nuclear matter acts like a nearly perfect fluid • v2 ~ constant for 4 < pT < 8 GeV

  26. Do partons or hadrons flow? • v2 per valence quark • pT quark = ½ pT (meson) • pT(quark) = 1/3 pT (baryon) • v2(quark) = 1/2 v2 (meson) • v2(quark) = 1/3 v2 (baryon) • Factor of 6 for deuterons • Evidence that partons flow, not hadrons • Valence quark model works well • Expected from quark recombination v2 per quark pT per quark Fabrice Retiere, QM2005

  27. Two-particle interferometry (HBT) • Hanbury-Brown Twiss interferometry gives 3-d system size • Enhancement of identical boson pairs with q = p1 - p2 <h/R •  : Fourier transform of the density distribution • 3-d Bertsch-Pratt parameterization qside qout qlong (z)

  28. System Size at Thermal Freezout • System size not very sensitive to collision energy • Source (Gaussian) radii ~ 6 fm • ~ 2X size of initial nuclei • Rout/Rside ~ 1 • Short emission time • explosive expansion • Modest variation with respect to reaction plane (elliptic flow) • Energy dependence, Rout/Rside ratio challenge most models Collision Energy

  29. High pT particles as probes of the medium g • High pT hadron production should be the same in pp, peripheral AA and central AA collisions • pQCD + universal fragmentation functions • Jet fragmentation occurs on a long time scale, outside the medium • True at high enough pT • Small differences from nuclear shadowing, proton:neutron ratio and initial state scattering • Differences in high pT hadron yields in AA vs. dA, pp are due to parton energy loss in the medium g q q Energy Loss in Medium?? Jet High pT hadron

  30. STAR dAu and AuAu • Compare AA, dA, pp using • QCD gives RAA=1 • RAA ~>1 for dAu • Initial state scattering gives partons pT • RAA ~ 1 for direct photons in AA • Photons do not lose energy • RAA ~ 0.2 for p0 in AuAu • 4 < pT < 20 GeV • Energy loss seems very large • Energy loss >> calculations based on interactions with hadrons • In pQCD calculations, requires very large (unphysical) gluon densities or cross sections pT pT

  31. Energy Loss Scaling • System size • AuAu, CuCu have similar energy loss for same Npart • Energy loss scales smoothly with system size • No clear ‘transition’ • Beam energy • No large suppression seen at SPS energies • Species • RAA larger for strange particles & baryons • Known strangeness, baryon enhancement RAA NPart

  32. Semileptonic decay of charm and bottom RAA ~ 0.2, same as for lighter hadrons Lower quark velocity suppresses small angle gluon radiation ‘Dead cone’ Less energy loss than for light quarks Cannot explain light and heavy quark energy loss simultaneously RAA for electrons from heavy quark decay RAA(h)

  33. Trigger Df= fT – fA Associated 2-particle azimuthal angle (Df) correlations • High pT ‘trigger’ + lower pT ‘associated’ particle • Single jets --> small Df correlations • dA, AuAu data similar to pp • Jets • Dijets --> back to back correlations (Df = p) • Peak in dAu & peripheral AuAu • Suppressed in central AuAu • Peak disappears for smaller trigger pT • Surface emission?? • Only partons produced near surface escape pTtrigger>8 GeV/c Yield per trigger Df (radians)

  34. STAR, Phys Rev Lett 95, 152301 Angular correlation widths Look at low pT recoils… • No pT cut onassociated track • Background is much larger • Flow introduces correlated background • ‘Near’ peak widths • Df unchanged • Dh broadened • Interactions with longitudinally expanding system • Back-to-back peak • Df Peak appears • 2X wider than dAu • Possible ‘wings’/Mach cone? • Energy conservation produces some back-to-back correlations 3<pT,trigger<4 GeV pT,assoc.>2 GeV Au+Au 0-10% Dh Df

  35. near near Medium Medium away away mach cone deflected jets High pT trigger 3 particle correlations • High pT partons in dense media might radiate in a Mach (shock wave) cone • Produces 3-particle correlations • Background subtraction very tricky • PHENIX may see, STAR may not Ridges may indicate conic radiation PHENIX Preliminary

  36. J/Y suppression • Quarkonium should ‘melt’ in a QGP • J/Y, Y’,. c states,… melt at different temperatures • J/Y melt at ~ 1.5 - 2.0 Tcritical • J/Y production was suppressed at the CERN SPS • More suppression than expected due to absorption in cold nuclear matter Mee (GeV)

  37. J/Y Summary • RAA ~ 0.3 in central collisions • A bit larger than for other particles • Similar to RAA(J/Y) at the SPS • ‘Should’ be larger at RHIC • Suppression scales smoothly with number of collisions (system size) • No break in spectrum, as was seen at SPS • Similar behavior at 62 and 200 GeV

  38. AuAu data summary • Initial energy density >> expected critical energy for a QGP • System is described by an expanding fireball, with <bT> =0.55, T=106 MeV • Anisotropic flow is large, at hydrodynamic limit • System acts like a liquid • Production of high pT particles is suppressed • Very small 2-particle back-to-back high pT correlations • Heavy quarks behave similar to light • J/y production is suppressed by ~ 1/3, similar to SPS

  39. Puzzles • The observed high pT suppression and large flow appear to require either very high gluon densities or very high cross sections. • Why is the system size (and duration) measured by HBT so small (and independent of collision energy)? • Why are jets elongated in rapidity in central collisions?

  40. Surprise! Strong Coupling • Tc < T < 4 Tc is a strongly coupled regime for partons • Duality arguments relate strong coupled QCD to weak coupled string theory • Many colored bound states/resonances (qq, qg,ggg…) • Lightly bound -- > large radii • Rescattering cross sections 10-100X larger than pQCD • Huge cross sections & similar behavior seen for atomic Feshbach resonances and with ultra-cold 6Li • Atoms tuned (with a B field) to be barely bound • Extremely low viscosity produces large elliptic flow • High pT hadrons interact with these bound states and lose energy. • J/y melting is gradual; survive up to at least 2Tc • Other mesons can survive at temperatures above Tc • Strong coupling might explain many puzzles • Quantitative studies needed!! E. Shuryak, hep-ph/0405066

  41. ? Viscosity • Flow (v2) depends on shear viscosity/entropy (h/s) • Data shows h/s < 0.1 • RHIC nuclear matter is a much better fluid than water • h/s ~ 10 for water • Inconsistent with hadron gas and hot QGP calculations • Viscosity ~ 1/4p calculated for sQGP using duality arguments h/s X.N. Wang ICHEP06 T (MeV)

  42. Has RHIC seen the Quark Gluon Plasma? • Energy densities, temperature adequate, and partonic flow indicates equilibrium reached during partonic stage • Seems to meet definition – quarks and gluons interacting in equilibrium • But… the very strong interactions were not expected • New name: sQGP – strongly interacting quark gluon plasma

  43. RHIC Future – Short Term Lower energy AuAu • Ion low-energy-scan • search for tri-critical point • 500 GeV pp collisions, higher luminosity • Polarized structure functions • STAR: TOF system + vertex detector • High-statistics heavy-flavor production • PHENIX: Hadron blind tracker for intermediate mass dileptons • Vector meson mass shifts and chiral symmetry breaking 200 GeV RHIC Plasma

  44. Longer Term plans • RHIC II • 10X luminosity upgrade • Electron cooling of hadron beams • High current electron accelerator • Technically challenging • eRHIC • Polarized ep, eA collisions • Study cold nuclear matter • Heavy Ion physics at the LHC • Higher energy --> higher temperature, denser system • Will the LHC reach high enough temperatures to see signs (lower v2) of the weakly coupled QGP?

  45. Conclusions • In dAu collisions, forward particle production is suppressed and back-to-back correlations are reduced, consistent with saturation models. • In heavy-ion collisions, the system thermalizes quickly, and has a very high interaction cross section. • This is consistent with the expectations from a sQGP – strongly interacting QGP – per recent theoretical studies. • RHIC is awash in good data. • We need a comprehensive, quantitative theoretical framework.

  46. Backups/spares/rejects

  47. Direct Photons • Hadrons measure temperature at freeze-out • Direct photons may measure temperature earlier on • Large background from p0 decays • ‘Signal’ is QCD processes and thermal radiation • Data consistent with QCD + Thermal radiation • T ~590 MeV

  48. Ion Collisions at RHIC Initial State • The beam energy is large enough that the incident baryons (mostly) do not stop • (Mostly) baryon free high energy density central region • Energy goes into copious particle production • Collision region ~ (10 fm)3, lifetime ~ few 10-23 s Baryon free region Final State

  49. Chiral Symmetry Restoration • Expected in a Quark-Gluon Plasma • Light quarks lose mass • Meson masses, widths and branching ratios will change • F-->e+e- is experimentally accessible • Narrow(ish), leptonic final state • In f --> K+K-, kaons are also subject to medium effects • Br(f-->e+e-) = 3*10-4 • Rates are low • No changes seen

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