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A new kind of matter at the Relativistic Heavy Ion Collider?

A new kind of matter at the Relativistic Heavy Ion Collider?. Barbara V. Jacak Stony Brook May 3, 2004. The Physics of Heavy Ion Collisions. Create very high temperature and density matter similar to that existing ~1 m sec after the Big Bang

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A new kind of matter at the Relativistic Heavy Ion Collider?

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  1. A new kind of matter at the Relativistic Heavy Ion Collider? Barbara V. Jacak Stony Brook May 3, 2004

  2. The Physics of Heavy Ion Collisions • Create very high temperature and density matter • similar to that existing ~1 msec after the Big Bang • distance between hadrons comparable to that in neutron stars • study only in the lab – relics from Big Bang inaccessible • Goal is to characterize the hot, dense medium • expect QCD phase transition to quark gluon plasma • does medium behave as a plasma? • find density, temperature, radiation rate, collision frequency, conductivity, opacity, Debye screening length? • probes: passive (radiation) and those created in the collision • Collide Au + Au ions for maximum volume • s = 200 GeV/nucleon pair, p+p and d+A to compare

  3. At high temperature and density: force is screened by produced color-charges expect transition to free gas of quarks and gluons + +… Quantum Chromo Dynamic phase transition Colored quarks interact by exchange of gluons Color charge of gluons  gluons interact among themselves • theory is non-abelian • curious properties at large distance: • confinement of quarks in hadrons

  4. Karsch, Laermann, Peikert ‘99 ~15% from ideal gas of weakly interacting quarks & gluons e/T4 T/Tc Tc ~ 170 ± 10 MeV (1012 °K) e ~ 3 GeV/fm3 non-perturbative QCD - calculate on lattice required conditions to study quark gluon plasma

  5. QGP at RHIC? 1012 1010 1057 1051 1045 1039 Where are we?

  6. RHIC at Brookhaven National Laboratory RHIC collides p, Au ions: 200 GeV/nucleon in c.m. 10 times the energy previously available!

  7. STAR 4 complementary experiments

  8. Hard scattered or heavy q,g probes of plasma formed p, K, p, n, f, L, D, X, W, d, Hadrons reflect (thermal) properties when inelastic collisions stop (chemical freeze-out). g, g* e+e-, m+m- Real and virtual photons emitted as thermal radiation. probing early stage of heavy ion collision e, pressure builds up we focus on mid-rapidity (y=0), as it is the CM of colliding system 90° in the lab at collider

  9. p-p PRL 91 (2003) 241803 Good agreement with NLO pQCD Parton distribution functions Fragmentation functions Study simple complex systems: p+p, “p”+A, A+A collisions is QCD the right theory at RHIC? Perturbative for high p transfer processes?  pp collisions: itworks! Have a handle on initial NN interactions by scattering of q, g inside N We also need: p0

  10. ( pQCD x Ncoll) / background Vogelsang/CTEQ6 ( pQCD x Ncoll) / (background x Ncoll) [w/ the real suppression] [if there were no suppression] pQCD in Au+Au? direct photons At high pT, it also works! gTOT/gp0 Au+Au 200 GeV/A: 10% most central collisions Preliminary pT (GeV/c) []measured / []background = measured/background

  11. Energy  to beam direction per unit velocity || to beam pR2 2ct0 Is the energy density high enough? PRL87, 052301 (2001) Colliding system expands: • e 5.5 GeV/fm3 (200 GeV Au+Au) well above predicted transition! value is lower limit: longitudinal expansion rate, formation time overestimated

  12. Almond shape overlap region in coordinate space Collective effects? Pressure: a barometer called “elliptic flow” Origin: spatial anisotropy of the system when created, followed by multiple scattering of particles in the evolving system spatial anisotropy  momentum anisotropy v2: 2nd harmonic Fourier coefficient in azimuthal distribution of particles with respect to the reaction plane

  13. Preliminary STAR STAR Preliminary v2 measured by the experiments 200 GeV: 0.2< pt < 2.0 130 GeV: 0.075< pt < 2.0 200 GeV: 0.150< pt < 2.0 4-part cumulants v2=0.05 200 GeV: Preliminary - Consistent results - At 200 GeV better pronounced decrease of v2 for the most peripheral collisions.

  14. Hydro. Calculations Huovinen, P. Kolb, U. Heinz v2 reproduced by hydrodynamics • see large pressure buildup • anisotropy  happens fast •  early equilibration ! STAR PRL 86 (2001) 402 central Hydrodynamics assumes early equilibration Initial energy density is input Equation of state from lattice QCD Solve equations of motion

  15. Kolb, et al Collective effect probes early phase Hydrodynamics can reproduce magnitude of elliptic flow for p, p. BUT correct mass dependence requires softer than hadronic EOS!! NB: these calculations have viscosity = 0 medium behaves as an ideal liquid

  16. Pressure felt by all hadrons • v2 scales ~ with # of quarks! • evidence for quarks as relevant d.o.f. when pressure built up

  17. Lattice QCD shows qq resonant states at T > Tc, also implying high interaction cross sections Need large s for fast equilibration & large v2 Parton cascade using free q,g scattering cross sections underpredicts pressure

  18. Properties of this stuff? • Pressure built up during collision -> observed collectivity • viscosity small, interaction s large • Quasiparticles may experience binding, but • are not color neutral as at T<Tc. • Do we expect screening? • quark & gluon density is high… • estimate G = <PE>/<KE> • <PE>=g2/d = g2(~4-6)/(41/3T)<KE> ~ 3T so plasma parameter G ~ 3 • RHIC is in regime of strongly coupled plasma • As in warm, dense plasma at lower (but still high) T • But strong interaction rather than electromagnetic

  19. schematic view of jet production hadrons leading particle q q hadrons leading particle AA AA AA nucleon-nucleon cross section <Nbinary>/sinelp+p “external” probes of the medium Hard scattering of q,g early. Observe fast leading particles, back-back correlations Before creating hadron jets, scattered quarks induced to radiate energy (~ GeV/fm) by the colored medium -> jet quenching

  20. Au-Au s = 200 GeV: high pT suppressed! PRL91, 072301(2003)

  21. near side away side Medium is opaque! peripheral central look for the jet on the other side STAR PRL 90, 082302 (2003) Peripheral Au + Au Central Au + Au

  22. Au+Au 0-5% STAR Preliminary pT > 200 MeV Df • recover the energy in hadrons ~ 500 MeV. • comparable to <pT> of the bulk medium lost energy is thermalized preliminary Away side jet is significantly broadened

  23. *deuteron-gold control experiment with no suppression Property probed: density Induced gluon brehmsstrahlung pQCD calculation depends on number of scatterings Agreement with data: initial gluon density dNg/dy ~ 1100e ~ 15 GeV/fm3 hydro initial state same dAu d-Au Lowest energy radiation sensitive to infrared cutoff. Au-Au

  24. A puzzle PRL 91 (2003) 172301 • p/ ~1 at high pT • in central collisions • > p+p, d+Au > peripheral Au+Au >jets in e+e- • collisions

  25. R. Fries, et al pQCD spectrum shifted by 2.2 GeV Teff = 350 MeV Are extras from the thermal medium? Hydro. expansion at low pT + jet quenching at high pT. coalescence of boosted quarks into hadrons enhances mid pT hadrons baryons especially

  26. But jet-like properties too… Baryons scale  Ncoll ! ~RAA Mesons, including f are suppressed  Effect governed by quark content

  27. Allow fast quark to grab partner from medium are baryons from jets or not? • measure probability of jet-like partner for baryons & mesons in pT range of excess • decrease for baryons in most central Au+Au • expected from recombination of purely thermal quarks pions protons Many baryons ARE from jets, but medium modifies those jets

  28. Summary of medium properties • Extract from models, constrain by jet suppression & v2 • Values from I. Vitev; others consistent

  29. conclusions • Is there quark gluon plasma at RHIC? qualified “yes” • Intense debate in community about standard of proof • Evidence is mounting that RHIC creates a strongly coupled, opaque plasma • With aid of hydrodynamic, l-QCD and p-QCD models: • e ~ 15 GeV/fm3 • dNgluon/dy ~ 1000 • sint large for T < 2-3 Tc • Medium modifies hadronization of moderate energy jets • Will learn screening properties via cc bound states • Are poised to characterize this new kind of plasma • radiation rate, conductivity, collision frequency • Color Glass Condensate? Maybe at x ~ 10-3 (y>2)

  30. r/ ggg d + Au collisions cent/periph. (~RAA) Saturation of gluons in initial state(colored glass condensate) Mueller, McLerran, Kharzeev, … Wavefunction of low x (very soft) gluons overlap and the self-coupling gluons fuse. Saturation at higher x at RHIC vs. HERA due to nuclear size  suppressed jet cross section; no back-back pairs

  31. 0-20% most central Ncoll=779 40-90% most central Ncoll=45 20-40% most central Ncoll=296 NB: need temperature too! Color screening properties? Lattice predictions for heavy quarks Data inconclusive, but x50 underway

  32. Open charm: baseline is p+p collisions PHENIX PRELIMINARY Measure charm s via semi-leptonic decay to e+ & e- p0, h, photon conversions are measured and subtracted fit p+p data to get the baseline for d+Au and Au+Au.

  33. No large suppression as for light quarks! PHENIX PRELIMINARY Curves are the p+p fit, scaled by the number of binary collisions

  34. Implications of the results for QGP • Ample evidence for equilibration • initial dN(gluon)/dy ~ 1000, energy density ~ 15 GeV/fm3, energy loss ~ 7-10 GeV/fm • Very rapid, large pressure build up requires • parton interaction cross sections 50x perturbative s

  35. How to get 50 times pQCD s? spectral function • Lattice indicates that hadrons don’t all melt at Tc! • hc bound at 1.5 Tc Asakawa & Hatsuda, PRL92, 012001 (2004) • charmonium bound states up to ~ 1.7 Tc Karsch; Asakawa&Hatsuda • p, s survive as resonances Schaefer & Shuryak, PLB 356 , 147(1995) • q,g have thermal masses at high T. as runs up at T>Tc? (Shuryak and Zahed) • would cause strong rescattering qq  meson

  36. E. Shuryak

  37. Implications of the results for QGP • Ample evidence for equilibration • v2 & jet quenching measurements constrain initial gluon density, energy density, and energy loss • parton interaction cross sections 50x perturbative s • parton correlations at T>Tc • complicates cc bound states as deconfinement probes! • Hadronization by coalescence of thermal,flowing quarks • v2 & baryon abundances point to quark recombination as hadronization mechanism • Jet data imply must also include recombination between quarks fromjets and the thermalized medium •  medium modifies jet fragmentation!

  38. Also see evidence for equilibrated final state Calculate hadron yields in Grand Canonical ensemble Observed hadron ratios in agreement with thermal ratios! T(chemical freeze-out) ~ 175 MeV

  39. early universe 250 RHIC 200 quark-gluon plasma 150 SPS Lattice QCD AGS deconfinement chiral restauration thermal freeze-out 100 SIS hadron gas 50 neutron stars atomic nuclei 0 0 200 400 600 800 1000 1200 Baryonic Potential B [MeV] Locate RHIC on phase diagram From fit of yields vs. mass (grand canonical ensemble): Tch = 176 MeV mB = 41 MeV These are the conditions when hadrons stop interacting T Observed particles “freeze out” at/near the deconfinement boundary!

  40. v2 recombination of flowing quarks nucl-ex/0305013 • p above p for • pT < 2 GeV/c, in agreement with hydrodynamics • Then crosses over. • Values ~ saturate • at high pT • geometry? • v2/quark ~ constant •  create hadrons • by coalescence of • quarks from • boosted distribution

  41. No large suppression as for light quarks! The yellow band represents the set of alpha values consistent with the data at the 90% Confidence Level.

  42. Do see Cronin effect! (h++h-)/2 “Cronin” enhancement more pronounced in the charged hadron measurement Possibly larger effect in protons at mid pT Implication of RdAu? RHIC at too high x for gluon saturation… p0

  43. No CGC signal at mid-rapidity So, perhaps Rda G-sat. Rda pQCD >2 BFKL, DGLAP Xc(A) RHIC Pt (GeV/c) Pt (GeV/c) Log Q2 How about Color Glass Condensate? Central: Enhanced not suppressed PHENIX preliminary y=0 Peripheral d+Au (like p+p)

  44. d Au PhenixPreliminary But at forward rapidity reach smaller x y = 3.2 in deuteron direction  x  10-3 in Au nucleus Strong shadowing, maybe even saturation?

  45. Why no big energy loss for heavy quarks? no x4 suppression from peripheral to central, as predicted for dE/dx=-0.5GeV/fm! But (we squirm) - Is 40-70% peripheral enough? error bars still big!

  46. Why no energy loss for charm quarks? • “dead cone” predicted by Kharzeev and Dokshitzer, Phys. Lett. B519, 199 (1991) • Gluon bremsstrahlung: • kT2 = m2 tform/l transverse momentum of radiated gluon • m =pT in single scatt. l =mean free path • q ~ kT / w w = gluon energy • But radiation is suppressed below angles q0= Mq/Eq soft gluon distribution is dP = asCF/p dw/w kT2 dkT2/(kT2+ w2q02) 2 not small for heavy quarks! causes a dead cone

  47. Protons are flatter  velocity boost  to beam Result of pressure built up p, K, p, pbar spectra indicate pressure Look at “transverse mass” mT2 = pT2 + m02 — is distribution e-E/T? i.e. Boltzmann distribution from thermalized gas? yes !

  48. Evidence for equilibrated final hadronic state BRAHMS • Simple quark counting: K-/K+ = exp(2ms/T)exp(-2mq/T) = exp(2ms/T)(pbar/p)1/3 = (pbar/p)1/3 • local strangeness conservation K-/K+=(pbar/p)a a = 0.24±0.02 BRAHMS a = 0.20±0.01 for SPS • Good agreement with statistical-thermal model of Beccatini et al. (PRC64 2001) w/T=170 MeV From y=0 to 3 At y=0 PRL 90 102301 Mar. 2003

  49. v2 of mesons & baryons Au+Au at sNN=200GeV 1) High quality M.B. data!!! 2) Consistent between PHENIX and STAR pT < 2 GeV/c v2(light) > v2(heavy) pT > 2.5 GeV/c v2(light) < v2(heavy) Model: P.Huovinen, et al., Phys. Lett. B503, 58 (2001) v2

  50. QCD Phase Transition • Basic (i.e. hard) questions • how does process of quark confinement work? • how nature breaks symmetries  massive particles from ~ massless quarks • transition affects evolution of early universe • latent heat & surface tension  • matter inhomogeneity in evolving universe • equation of state  compression in stellar explosions • Study simple complex systems: p+p, “p”+A, A+A collisions

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