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 I can only hit the biggest highlights RHIC n RHIC was built to explore the properties of nuclear matter under extreme conditions u Polarized parton distributions u Cold nuclear matter - nuclei u Hot nuclear matter the QGP? n Study typical collisions, not rare events. The Relativistic Heavy Ion Collider h STAR PHENIX PHOBOS BRAHMS/ pp2pp n 2 concentric rings of 1740 superconducting magnets n 3.8 km circumference n counter-rotating beams of ions from p to Au Brookhaven National Laboratory RHIC datasets from Au to p n System size scan u AuAu & CuCu n Collision energy scan u 200, 130, 62, 22 GeV per nucleon n dAu n pp u Polarization up to 65% STAR: full acceptance Detector for global event reconstruction PHENIX: 2 arm spectrometer Good PID for rare probes PHOBOS: full acceptance BRAHMS: 2 precision spectrometers pp2pp: elastic scattering Other Physics n Polarized Protons and polarized parton distributions n Photoproduction n Search for strangelets in AuAu collisions Polarized parton studies n Quark, gluon polarization n Compare cross sections for proton polarizations in the same vs. in opposite directions n Longitudinally and transversely polarized beams u Many different structure functions Longitudinal Asymmetry PHENIX, 2006 A LL Photonuclear and two-photon interactions at RHIC n Ions support a large Weizscker- Williams photon flux u Photon flux ~ Z 2 n Copious photonuclear interactions u Coherent vector meson production has a large cross section RHIC has studied 0, 0 and J/ photoproduction in AuAu, 0 in dA n RHIC has studied two-photon production of e + e - u Rate ~ Z 4 n The LHC is the only place to study photoproduction at energies above HERA Au Pomeron J PHENIX J/ M ee (GeV) Unique Reactions n Cant tell if nucleus 1 or nucleus 2 emitted the photon u 2-source interferometer u Negative parity --> subtract amplitudes F + sign at pp colliders ~ |A 1 - A 2 e ipb | 2 At y=0 = 0 [1 - cos(p b)] n Large Z --> multiple reactions Au + Au --> Au* + Au* + 0 u 3 & 4 photon exchange dN/dt STAR Preliminary Data (w/ fit) MC no Interference MC - interference t ~ p T 2 (GeV 2 ) 0.1 < |y| < 0.5 - pp, dA and cold nuclear matter n pp collisions u tests of pQCD calculations n dA collisions u Use deuteron to probe gold nucleus F Cold nuclear matter F Parton distributions at low Feynman-x u Benchmark for studies of ion-ion collisions pp collisions & pQCD n Jet cross sections and high p T particle spectra are both well fit by pQCD + fragmentation functions u Thanks to recent theoretical advances 0 pT0 pT (Data-theory)/theory Hadron production at large p T : data vs. QCD Inclusive jets Jet p T (Data-theory)/theory d /dp T (mb/GeV) dAu collisions n Gluon density rises as x decreases and/or Q 2 increases u At high densities gluons overlap & densities saturate u Saturation occurs at larger x in nuclei F Shadowing reduced parton densities in ions, compared to nucleons n Many theoretical approaches u Evolution equations(BFKL/DGLAP) u Colored Glass Condensate describe gluons with a classical field Decreasing x --> Decreasing Q 2 --> Particle Production at Forward x BRAHMS, PRL 93, Sizable suppression in charged hadron production in d+Au collisions relative to p+p collisions at forward rapidity BRAHMS (dA)/ (pp) (central dA)/ (peripheral dA) Increasing Rapidity (decreasing x)---> Central Forward Is this a Colored Glass Condensate? n Suppression curves may be fit by multiple models n x= is moderate, not small n In lowest order pQCD g + g --> g + g (or q + q) produces back-to-back jets u Moderate higher order corrections n In a CGC, the target reacts coherently u g + target --> g + target u Heavy target absorbs the impact with little recoil u Monojets gg jet gCGC jet No jet pQCD Colored Glass Condensate 2 particle correlations Azimuthal angle correlations between forward 0 and central h correlations in pp and dAu u If a CGC is present in Au, correlation should be smaller in dA n Correlations smaller in dA than pp u More suppression at small p T --> smaller x u Consistent with CGC nucl-ex/ 0 : | | = 4.0 h : | | 0.5 GeV/c STAR Forward 0 trigger Mid-rapidity h h Heavy ion collisions and hot nuclear matter n Hot nuclear matter is produced by colliding heavy ions n Study the properties of hot nuclear matter n Search for the Quark Gluon Plasma u Interacting quarks and gluons, in equilibrium u Individual nucleons disappear Quark Gluon Plasma quarks+ gluons Normal Nucleus protons + neutrons or Nuclear matter phase diagram Phase boundaries calculated with lattice QCD Transition temperature T c ~ 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 Plasma Space-Time evolution Chemical freezeout: inelastic scattering stops Chemical Composition Initial Collisions: hard probes produced high p T particles charm Thermal freezeout: elastic scattering stops Global characteristics Particle Spectra Elliptic Flow HBT Outgoing baryons Central Region Observables in ion collisions n Impact parameter (b) and centrality u N part and N bin n System composition and thermal equilibrium n Expanding fireball (blast wave) model n Nuclear flow & hydrodynamics n System size quantum (HBT) interferometry n High p T particles and nuclear energy loss n Particle Correlations J/ suppression Impact parameter and centrality determination n Impact parameter (b) is not directly observable u Charged particle multiplicity or E T u Spectator neutrons n Common variables u N part number of nucleons involved in collision u N bin number of nucleon-nucleon collisions F Important for hard probes u %age of collision F e.g. 0-10% most central N h- d /dN h- Log scale! b=0 N part =2A N bin ~ A 2 b ~ R A spectators Charged particle Distributions Pseudorapidity related to longitudinal velocity u Neglecting particle mass n Rapidity plateau dN/d ~ constant for | | > calculations based on interactions with hadrons u In pQCD calculations, requires very large (unphysical) gluon densities or cross sections dAu and AuAuSTAR pTpT pTpT Energy Loss Scaling n System size u AuAu, CuCu have similar energy loss for same N part u Energy loss scales smoothly with system size u No clear transition n Beam energy u No large suppression seen at SPS energies n Species u R AA larger for strange particles & baryons F Known strangeness, baryon enhancement R AA N Part R AA for electrons from heavy quark decay n Semileptonic decay of charm and bottom n R AA ~ 0.2, same as for lighter hadrons n Lower quark velocity suppresses small angle gluon radiation u Dead cone u Less energy loss than for light quarks n Cannot explain light and heavy quark energy loss simultaneously R AA (h) 2-particle azimuthal angle ( ) correlations n High p T trigger + lower p T associated particle Single jets --> small correlations u dA, AuAu data similar to pp u Jets Dijets --> back to back correlations ( = ) u Peak in dAu & peripheral AuAu u Suppressed in central AuAu F Peak disappears for smaller trigger p T n Surface emission?? u Only partons produced near surface escape p T trigger >8 GeV/c Yield per trigger (radians) Trigger Associated A Au+Au 0-10% 3

2 GeV Angular correlation widths n No p T cut on associated track u Background is much larger u Flow introduces correlated background n Near peak widths unchanged broadened F Interactions with longitudinally expanding system n Back-to-back peak Peak appears F 2X wider than dAu F Possible wings/Mach cone? u Energy conservation produces some back-to-back correlations Look at low p T recoils STAR, Phys Rev Lett 95, 3 particle correlations n High p T partons in dense media might radiate in a Mach (shock wave) cone u Produces 3-particle correlations u Background subtraction very tricky n PHENIX may see, STAR may not PHENIX Preliminary Ridges may indicate conic radiation away near Medium mach cone Medium away near deflected jets High p T trigger J/ suppression n Quarkonium should melt in a QGP J/ , ,. states, melt at different temperatures J/ melt at ~ T critical J/ production was suppressed at the CERN SPS u More suppression than expected due to absorption in cold nuclear matter M ee (GeV) J/ Summary n R AA ~ 0.3 in central collisions u A bit larger than for other particles Similar to R AA (J/ ) at the SPS F Should be larger at RHIC n Suppression scales smoothly with number of collisions (system size) u No break in spectrum, as was seen at SPS n Similar behavior at 62 and 200 GeV AuAu data summary n Initial energy density >> expected critical energy for a QGP System is described by an expanding fireball, with =0.55, T=106 MeV n Anisotropic flow is large, at hydrodynamic limit u System acts like a liquid n Production of high p T particles is suppressed u Very small 2-particle back-to-back high p T correlations u Heavy quarks behave similar to light J/ production is suppressed by ~ 1/3, similar to SPS Puzzles n The observed high p T suppression and large flow appear to require either very high gluon densities or very high cross sections. n Why is the system size (and duration) measured by HBT so small (and independent of collision energy)? n Why are jets elongated in rapidity in central collisions? Surprise! Strong Coupling n T c < T < 4 T c is a strongly coupled regime for partons u Duality arguments relate strong coupled QCD to weak coupled string theory u Many colored bound states/resonances (qq, qg,ggg) F Lightly bound -- > large radii F Rescattering cross sections X larger than pQCD Huge cross sections & similar behavior seen for atomic Feshbach resonances and with ultra-cold 6 Li Atoms tuned (with a B field) to be barely bound F Extremely low viscosity produces large elliptic flow F High p T hadrons interact with these bound states and lose energy. J/ melting is gradual; survive up to at least 2T c u Other mesons can survive at temperatures above T c n Strong coupling might explain many puzzles u Quantitative studies needed!! E. Shuryak, hep-ph/ ? X.N. Wang ICHEP06 Viscosity /s Flow (v 2 ) depends on shear viscosity/entropy ( /s) Data shows /s < 0.1 n RHIC nuclear matter is a much better fluid than water /s ~ 10 for water n Inconsistent with hadron gas and hot QGP calculations Viscosity ~ 1/4 calculated for sQGP using duality arguments T (MeV) Has RHIC seen the Quark Gluon Plasma? n Energy densities, temperature adequate, and partonic flow indicates equilibrium reached during partonic stage u Seems to meet definition quarks and gluons interacting in equilibrium n But the very strong interactions were not expected u New name: sQGP strongly interacting quark gluon plasma RHIC Future Short Term n Ion low-energy-scan u search for tri-critical point n 500 GeV pp collisions, higher luminosity u Polarized structure functions n STAR: TOF system + vertex detector u High-statistics heavy-flavor production n PHENIX: Hadron blind tracker for intermediate mass dileptons u Vector meson mass shifts and chiral symmetry breaking 200 GeV RHIC Lower energy AuAu Plasma Longer Term plans n RHIC II u 10X luminosity upgrade u Electron cooling of hadron beams F High current electron accelerator F Technically challenging n eRHIC u Polarized ep, eA collisions u Study cold nuclear matter n Heavy Ion physics at the LHC u Higher energy --> higher temperature, denser system u Will the LHC reach high enough temperatures to see signs (lower v 2 ) of the weakly coupled QGP? Conclusions n In dAu collisions, forward particle production is suppressed and back-to-back correlations are reduced, consistent with saturation models. n In heavy-ion collisions, the system thermalizes quickly, and has a very high interaction cross section. u This is consistent with the expectations from a sQGP strongly interacting QGP per recent theoretical studies. n RHIC is awash in good data. u We need a comprehensive, quantitative theoretical framework. Backups/spares/rejects Direct Photons n Hadrons measure temperature at freeze-out n Direct photons may measure temperature earlier on Large background from 0 decays n Signal is QCD processes and thermal radiation n Data consistent with QCD + Thermal radiation u T ~590 MeV Ion Collisions at RHIC n The beam energy is large enough that the incident baryons (mostly) do not stop u (Mostly) baryon free high energy density central region u Energy goes into copious particle production n Collision region ~ (10 fm) 3, lifetime ~ few s Initial State Final State Baryon free region Chiral Symmetry Restoration n Expected in a Quark-Gluon Plasma n Light quarks lose mass n Meson masses, widths and branching ratios will change -->e + e - is experimentally accessible u Narrow(ish), leptonic final state In --> K + K -, kaons are also subject to medium effects Br( -->e + e - ) = 3*10 -4 F Rates are low u No changes seen Charm Production n Charm is too heavy for thermal production u pQCD calculations should apply Direct Photons n Hadrons measure temperature at freeze-out n Direct photons may measure temperature earlier on Large background from 0 decays n Signal is QCD processes and thermal radiation n Data consistent with QCD + Thermal radiation u T ~590 MeV Flavor, Baryon number dependence K S, similar to h u has slightly less suppression n R AA for baryons larger than for mesons n R AA increases with strangeness u Lack of strangeness suppression F System size effect 0-5% Au+Au p+p STAR Preliminary s NN =200 GeV 2-d angular correlations n 2 GeV/c > p T > 100 MeV/c n 2 charged-particle angular correlations vs Peak at Small & from jets Jets are broadened in in central collisions F Seen by several analyses, not well understood Cos(2 ) modulation from flow Contribution at from back- to-back jets Central Mid-central Peripheral STAR, 2006 pp2pp : small angle p p Elastic Scattering at RHIC Re r 5 = 0.035, Im r 5 = 0.56 Phys. Lett. B 632, (2006) The pp2pp Roman pots are now being moved to STAR, to study central production of resonances in pp diffractive events. pp2pp will measure: 1.Total and elastic cross sections in pp collisions; 2.Single and double diffraction in pp collisions; (important to modeling and interpretation of cosmic ray shower data.) 3.Spin dependence of elastic scattering;.