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RHIC Physics Overview Where do we stand?

RHIC Physics Overview Where do we stand?. Thomas Ullrich, BNL RHIC Retreat Port Jefferson June 7, 2004. Exploring the Phases of QCD. Rajagopal and Wilczek, hep-ph/-0011333. Definition of QGP. Theoretical expectations of its properties evolved over the last 20 years For our purpose:

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RHIC Physics Overview Where do we stand?

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  1. RHIC Physics OverviewWhere do we stand? Thomas Ullrich, BNL RHIC Retreat Port Jefferson June 7, 2004

  2. Exploring the Phases of QCD Rajagopal and Wilczek, hep-ph/-0011333

  3. Definition of QGP Theoretical expectations of its properties evolved over the last 20 years • For our purpose: “A locally thermally equilibrated state of matter in which quarks and gluons are deconfined from hadrons, so that color degrees of freedom become manifest over nuclear, rather than merely nucleonic, volumes.” • We do not demand: • quarks and gluons are non-interacting (sQGP vs. wQGP) • do not require a first or second order phase transition

  4. G. Schierholz et al., Confinement 2003 Action density in 3 quark system in full QCD H. Ichie et al., hep-lat/0212036 Lattice QCD at Finite Temperature • Coincident transitions: deconfinement and chiral symmetry restoration • Recently extended tomB> 0, order still unclear (2nd, crossover ?) Critical energy density: eC = (62)TC4 F. Karsch, E. Laermann, A. Peikert, Nucl. Phys. B605 (2001) 579 TC~ 1758 sys MeV eC ~ 0.3-1.3 GeV/fm3

  5. The Phase Transition in the Laboratory

  6. 0 1 2 3 4 5 6 7 8 9 10 11 12 GeV/c Hydro ReCo pQCD What addresses what: pT scale is the key Different physics for different scales

  7. z y x Reaction plane Geometry of a Heavy-Ion Collision Non-central collision Number of participants (Npart):number of incoming nucleons (participants) in the overlap region Number of binary collisions (Nbin): number of equivalent inelastic nucleon-nucleon collisions Nbin Npart

  8. E895 E895 E895 NA49 NA49 Rapidity Distributions of Charged Particles 19.6 GeV 130 GeV 200 GeV PRL 91, 052303 (2003) AuAu Rapidity y  Pseudorapidity h AGS & SPS: no central plateau in y At RHIC: very small plateau only |h|<0.5  Boost invariance only achieved in small region |y|<0.5  3.1 GeV Au+Au 3.6 GeVAu+Au 4.1 GeVAu+Au 200 GeVAu+Au 8.8 GeVPb+Pb 17.3 GeVPb+Pb BRAHMS

  9. Scaling of Charged Multiplicity PHOBOS 200 GeV Au+Au PHOBOS Preliminary arXiv:nucl-ex/0301017 Nouicer et al., QM2004 Nch scales with Npart

  10. Particle Density near Mid-Rapidity Models prior to RHIC • Total Nch ~ 5000 (Au+Au s = 200 GeV)  ~ 20 in p+p • Nch/Nparticipant-pair ~ 4 (central region)  ~2.5 in p+p • eRHIC > 5 GeV/fm3  eC ~ 1 GeV/fm3 (lattice) • It makes no sense to describe it in terms of simplehadronic degrees of freedom PRL 85, 3100 (2000) PRL 88, 22302 (2002) PRL 91, 052303 (2003) In Au+Au Collisions at sNN = 200 GeV: • Maximum released energy is at mid-rapidity • In a system at rest with the center of mass: e > 5 GeV/fm3

  11. Is there a way to assess temperature? • Where in the phase diagram (T, B) is the system at chemical freeze-out? • What values have Tch, B ? • Statistical Thermal Models: a means to extract (Tch, B) from particle ratios Statistical Thermal Models F. Becattini; P. Braun-Munzinger, J. Stachel, D. Magestro, J.Rafelski, J.Sollfrank et al. Assume: Ideal hadron resonance gas thermally and chemically equilibrated Recipe: grand canonical partition function  density of particles I Input: measured particle ratios Output: temperature T and baryo-chemical potential B

  12. Ratios of Hadrons at RHIC Plenty of integrated hadron yields available • Long lived hadrons • very well described by statistical models Tch = 160-170 MeV • close to TC (but also close to Hagedorn limit for hadron gas) • Short lived resonances • deviation from thermal fits •  fair amount of hadronic scattering after chemical freeze-out

  13. Chemical Freeze-Out Temperature Close to Tc Statistical models: Hint that chemical and thermal equilibrium is reached (but no proof!) If true (?): Tch TC implies that hadrons are born into equilibrium

  14. Central AuAu √s = 200 GeV light 1/mT dN/dmT heavy mT Hydro (P. Kolb & U. Heinz) With initial flow kick explosive source light purely thermal source T,b 1/mT dN/dmT heavy T mT “Thermal” Spectra and Flow • Final state spectra reflect the system at thermal freeze-out • Two components • “temperature” T • collective radial (transverse) flow bT • The stronger the flow the less appropriate are simple exponential fits: • Hydrodynamic models • Hydro inspired parameterizations • (Blastwave) Low-pt spectra mostly plotted versus: mT = (pT2+m2)1/2

  15. Hydrodynamics: Modeling the Ideal Liquid • Assumes local thermal equilibrium (zero mean-free-path limit) and solves equations of motion for fluid elements (not particles) • Equations given by continuity, conservation laws, and Equation of State (EOS) • EOS relates quantities like pressure, temperature, chemical potential, volume • direct access to underlying physics Kolb, Sollfrank & Heinz, hep-ph/0006129 lattice QCD input

  16. PHOBOS Au+Au sNN=200 GeV 15% central -0.1< y <0.4 arXiv:nucl-ex/0401006 Identified particle spectra in Au+Au @ 200 GeV STAR and PHENIX data PHENIX Phys. Rev. C 69, 034909 (2004) STAR Nucl. Phys. A715 466c (2003) STAR nucl-ex/0403032

  17. Kolb, Sollfrank & Heinz, hep-ph/0006129 Interpretation of particle spectra at low-pT • Rescattering • in partonic phase  radial flow bT • in hadronic phase  radial flow bT • How to distinguish ? • multi-strange hadrons and charm mesons have small  for rescattering once formed  should decouple early from system  T and bT should differ from p, K, p

  18. Interpretation of particle spectra at low-pT • This is one of the most statistics hungry study at RICH • For light hadrons we observe • large radial flow bT ~ 0.6 c • Tfreeze-out ~ 100 MeV • Multi-strange particles appear to behave differently: • slightly lower bT • considerable larger T • Hint for partonic flow (jury still out)

  19. Au+Au at b=7 fm P. Kolb, J. Sollfrank, and U. Heinz t2 t3 t1 t4 Elliptic Flow: v2 Reaction Plane Elliptic flow observable sensitive to early evolution of system Mechanism is self-quenching Large v2 is an indication of early thermalization Almond shape overlap region in coordinate space Interactions/ Rescattering Anisotropy in momentum space Equal energy density lines

  20. Hydrodynamic limit STAR PHOBOS Compilation and Figure from M. Kaneta Charged hadron elliptic flow PHOBOS: Phys. Rev. Lett. 89, 222301 (2002) First time in Heavy-Ion Collisions a system created which is in quantitative agreement with ideal hydrodynamic model predictions for v2 Rather smooth dependence versus beam energy Phys.Rev. C68 (2003) 034903 NA49 STAR: Phys. Rev. Lett. 86, 402 (2001) RQMD

  21. Belt-Tonjes et al., QM2004 The Hyperfine Structure: v2(m,pT,h) PHENIX Consistent measurements from RHIC experiments • Hydrodynamical models with soft Equation-of-State (EOS) describe hyperfine structure well for pT (< 2.5 GeV/c) v2(p) > v2(K) > v2 (p) > v2(L) • compatible with early equilibration No hydro models yet to describe rapidity dependence (3D hydro)

  22. New: Comparison of v2 at 62.4 and 200 GeV v2(pT) T. Awes, User Meeting 2004 pT GeV/c Puzzling (but very interesting) result: v2 (even with PID) at 62.4 GeV looks like 200 GeV results  Integral v2 will be lower since pT decreases

  23. 0 1 2 3 4 5 6 7 8 9 10 11 12 GeV/c Hydro ReCo pQCD What addresses what: pT scale is the key Different physics for different scales

  24. Baryon/Meson Ratios Baryon/meson ratio “anomalous” for pT<6-7 GeV/c

  25. p/p Anomaly also in Au+Au at 62.4 GeV • Central p/p+ ratio similar to 200 GeV Au+Au result at high pT. • Centralp/p- ratio at 2-3 GeV is smaller than 200 GeV results. • Smallerp/p ratio due to more baryon transport to mid-rapidity and lessp-p production. T. Awes, User Meeting 2004

  26. The Definition of RCP Compare different Au+Au centralities  RCP Nuclear Modification Factor: R < 1 at small momenta (Npart scaling) R = 1 baseline expectation for hard processes (Nbin scaling) R > 1 “Cronin” enhancements (as in pA)R < 1: Suppression

  27. Suppression of identified particles Mass or meson/baryon effect? PHENIX: PRL 91, 172301 L L show different behaviour to K Suppression ofK sets in at lower pT K Come together again at pT ~ 6 GeV? “standard” fragmentation? • Not a mass dependence! • Two groups (2 < pT< 6 GeV/c): • K0s, K, K*, f  mesons • L, X, W baryons

  28. Recombination Models • The in vacuofragmentation of a high momentum quarkto produce hadrons competes with the in mediumrecombinationof lower momentum quarks to produce hadrons • Example: • Fragmentation: Dq→h(z) • produces a 6 GeV/c pfrom a 10 GeV/c quark • Recombination: • produces a 6 GeV/c pfrom two 3 GeV/c quarks • produces a 6 GeV/c protonfrom three 2 GeV/c quarks ...requires the assumption of a thermalized parton phase... (which) may be appropriately called a quark-gluon plasma Fries, et al, PRC 68, 044902 (2003) Lepez, Parikh, Siemens, PRL 53 (1984) 1216

  29. Recombination Extended • The complicated observed flow pattern in v2(pT) for hadrons • is predicted to be simple at the quark level underpT → pT /n • v2 → v2 / n , • n = (2, 3) for (meson, baryon) • If the flow pattern is established at the quark level • Works for p, p, K0s,  &  • v2s ~ v2u,d ~ 7% STAR Preliminary Au+Au sNN=200 GeV MinBias 0-80% D. Molnar, S.A. Voloshin Phys. Rev. Lett. 91, 092301 (2003) V. Greco, C.M. Ko, P. Levai Phys. Rev. C68, 034904 (2003) R.J. Fries, B. Muller, C. Nonaka, S.A. Bass Phys. Rev. C68, 044902 (2003) Z. Lin, C.M. Ko Phys. Rev. Lett. 89, 202302 (2002)

  30. 0 1 2 3 4 5 6 7 8 9 10 11 12 GeV/c Hydro ReCo pQCD What addresses what: pT scale is the key Different physics for different scales

  31. q q c a b d Probing the Density • Using probes that are: • Auto-generated  initial hard scatterings • Traverse the medium  interact with the medium • Calculable in pQCD • Calibrated  measured in p+p • Have known scaling properties  Nbin scaling of hard processes These features no available prior to RHIC • Energy Loss via induced gluon bremsstrahlung: • measures gluon density • not a probe for deconfinement

  32. Jets at RHIC? pp jet+jet Au+Au ??? Hopeless?

  33. Measure Energy loss via “Leading Hadrons” Energy loss  softening of fragmentation products suppression of leading hadron yield

  34. How to measure? Compare Au+Au with p+p Collisions  RAA A+A yield Nuclear Modification Factor: p+p cross section <Nbinary>/sinelp+p R < 1 at small momenta R = 1 baseline expectation for hard processes R > 1 “Cronin” enhancements (as in pA)R < 1: Suppression

  35. Reference Spectra: p+p @ 200 GeV Good theoretical (NLO pQCD) description ... p+p p0 Xp+p h±X (non singly diffractive) (PDF: CTEQ6M) PHENIX Collab. PRL91, 241803 hep-ex/0304038 KKP FF Kretzer FF • Well calibrated (experimentally & • theoretically) p+p references at hand !

  36. Au+Au @ 200 GeV (central):Suppression RAA << 1: well below pQCD (collinear factorization) expectations for hard scattering cross-section p0 x 4-5 suppression h+/- x 4-5 suppression Discovery of high pT suppression (one of most significant results @ RHIC so far)

  37. Is suppression an initial or final state effect? Initial state? Final state? partonic energy loss gluon saturation strong nuclear effects in the initial-state How to discriminate? Turn off final state d+Au collisions no partonic energy loss strong nuclear effects in the initial-state

  38. d+Au @ 200 GeV: Enhancement Suppression in central Au+Au due to final-state effects

  39. Trigger particle Near side jet  Associated particles Correlation of trigger particles 4<pT<6.5 GeV withassociated particles 2<pT<pT,trig Away side jet 2-Particle Azimuthal Distributions Near side Df 0: p+p, d+Au, Au+Au similar Back-to-back Df p : Au+Au suppressed relative to p+p and d+Au

  40. Di-Jet Tomography: Reaction Plane Dependence • Au+Au Away-side suppression • in out-of-plane direction larger than in in-plane • Effect of path length on suppression is experimentally accessible

  41. Theory vs. data  very dense medium Medium properties according to “jet quenching” models: Initial gluon densities: dNg/dy ~ 1100 [Vitev & Gyulassy] Opacities: L/≈ 3 – 4 [Levai et al.] Transport coefficients: <q 0> ~ 3.5 GeV/fm2 [BDMPS, F.Arleo ] Plasma temperatures: T ~ 0.4 GeV [G. Moore] Medium-induced radiative energy losses: [X.N.Wang] dE/dx ≈ 0.25 GeV/fm (expanding) dE/dx|eff ≈ 14 GeV/fm (static source) Such large opacities imply: (i) large rescattering: thermalization (ii) energy densities εcrit QCD >> 1 GeV/fm3

  42. Evolution of RAA The reason for looking at s = 63 GeV (and 20 GeV ?) ?

  43. Au+Au @ 62.4 GeV: pT spectra nucl-ex/0405003 0-10% p0 10-30% p0 0-85% p0 π0 preliminary

  44. New: Preliminary Au+Au @ 62.4 GeV RAA Preliminary Result: Constant suppression at high pT: RAA ~ 0.3 for pT > 6 GeV/c Not unlikely to result at 200 GeV

  45. Suppression in d+Au at Forward Rapidities RdA and RCP: • Clear suppression towards h = 3 • Various Interpretations: • Gluon Saturation (Color Glass Condensate) • Beam fragmentation and string breaking (S. Brodsky and J. Gunion) • jury is still out

  46. Large Dhp0+h± correlations • Suppressed at small <xF> , <pT,p> • Consistent with CGC picture • D.Kharzeev, E. Levin, L. McLerran gives physics picture (hep-ph/0403271) , but no quantitative predictions available (yet) • Consistent in d+Au and p+p at larger <xF> and <pT,p> • as expected by HIJING 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) f 25<Ep<35GeV STAR Preliminary Fixed h, as E & pT grows 35<Ep<45GeV Statistical errors only d+Au Correlations: probing low x

  47. Run 1: • Collective flow (v2, bT) • First hint of high-pT suppression • Bulk properties (Nch, ET, pT) • ppHBT • Run 2: • More detailed picture on high-pT suppression • pT < 12 GeV/c • Way-side jet suppression • vs. in/out of reaction plane (2 bins) • flow: v1, v2, v4, v6, v2 fine structure • identified spectra (pT range ~ 1-8 GeV/c) • HBT vs. reaction plane • First data on direct photons (non-thermal) • Run 3 (d+Au): • High-pT suppression is final state effect • Hint for CGC ? Au+Au: From Run 1- Run 4 The scientific progress at RHIC  performance of the machine and coverage and capabilities of the experiments Working on the analysis of Run 4 …

  48. 1 + (g pQCD direct x Ncoll) / gphenix backgrd Vogelsang NLO 1 + (g pQCD direct x Ncoll) / gphenix backgrd Vogelsang, mscale = 0.5, 2.0 1 + (g pQCD direct x Ncoll) / (gphenix pp backgrd x Ncoll) Expect more on: Direct Photons in Au+Au … Both d+Au RAA and Direct g results imply that high pT suppression is not an initial state effect.Initial state explanation of suppression is laid to rest! PHENIX Preliminary PbGl / PbSc Combined 3/4 g are Direct! g-Jet studies feasible! Direct g AuAu 200 GeV Central 0-10% (g direct + gexp. bkgd.) / gexp. bkgd. = 1 + (gdirect/gexp. bkgd.) T. Awes, User Meeting 2004

  49. J/Y->e+e- J/Y->m+m- Minv (GeV) 2 Minv (GeV) … J/Y and Single Electrons … PHENIX electron and J/Y measurement! Clear J/Y signal already observed by muon and electron arms in a small subset of Run-4 Au+Au data. PHENIX PRELIMINARY ~ x100 more data in Run-4! See Wei Xie and Gerd Kunde’s talk T. Awes, User Meeting 2004

  50. … Open Charm and Beauty … STAR electron from TPC,TOF & EMC -- Tom Cormier direct open charm from TPC -- An Tai STAR Preliminary Charm Beauty RHIC Exp Program from PHENIX and STAR: Au+Au data on charm and beauty ,Charm flow, J/y and Upsilon ! Detector Upgrade: PHENIX -- VTX STAR -- TOF and microVertex Detector (MVD) ! H. Huan, User Meeting 2004

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