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Hard probes of hot, dense matter at RHIC

Hard probes of hot, dense matter at RHIC. Report from PHENIX. Barbara V. Jacak Stony Brook Sept. 20, 2003. Collide heavy ions at RHIC to. Create very high temperature and density matter as existed ~1 m sec after the Big Bang inter-hadron distances comparable to that in neutron stars

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Hard probes of hot, dense matter at RHIC

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  1. Hard probes of hot, dense matter at RHIC Report from PHENIX Barbara V. Jacak Stony Brook Sept. 20, 2003

  2. Collide heavy ions at RHIC to • Create very high temperature and density matter • as existed ~1 msec after the Big Bang • inter-hadron distances comparable to that in neutron stars • collide heavy ions to achieve maximum volume • Study the hot, dense medium • is thermal equilibrium reached? • transport properties? equation of state? • do the nuclei dissolve into a quark gluon plasma? • Au + Au at s = 200 GeV/nucleon pair • p+p and d+A to compare • Also polarized p+p collisions to study carriers of p’s spin

  3. vacuum QGP did something new happen at RHIC? • Study collision dynamics (via final state) • Probe the early (hot) phase Equilibrium? hadron spectra, yields Collective behavior i.e. pressure and expansion? elliptic, radial flow Particles created early in predictable quantity interact differently in QGP vs. hadron matter fast quarks, J/Y, strange quark content, thermal radiation

  4. p-p hep-ex/0304038 Good agreement with NLO pQCD Parton distribution functions Fragmentation functions s = 200 GeV, hard probesstart with pQCD & pp collisions Works! A handle on initial NN interactions by scattering of q, g inside N We also need: p0

  5. EOS Karsch, Laermann, Peikert ‘99 e/T4 Tc ~ 170 ± 10 MeV (1012 °K) e ~ 3 GeV/fm3 In A+A: QCD in non-perturbative regime Lattice… we look for physics beyond simple superposition of NN: Equilibration Collective effects Energy, color transport in dense medium Deconfinement? Physics is soft! T/Tc Lattice QCD says: Create these conditions to look for new physics

  6. RHIC at Brookhaven National Laboratory RHIC is first dedicated heavy ion collider 10 times the energy previously available!

  7. PHENIX at RHIC 2 Central spectrometers 2 Forward spectrometers 3 Global detectors

  8. We follow history of heavy ion collisions high e, pressure builds up g, g* e+e-, m+m- p, K, p, n, f, h, L, d Real and virtual photons from q scattering sensitive to the early stages. Probe also with q and g produced early, & passing through the medium on their way out. Hadrons reflect medium properties when inelastic collisions stop (chemical freeze-out).

  9. Colliding system expands: Energy  to beam direction per unit velocity || to beam pR2 • e 4.6 GeV/fm3 (130 GeV Au+Au) 5.5 GeV/fm3 (200 GeV Au+Au) 2ct0 well above predicted transition! Is the energy density high enough? PRL87, 052301 (2001)

  10. hydrodynamic analysis of spectra Au+Au at s = 130 GeV nucl-ex/0307010 Simultaneous fit to mT-m0 < 1 Gev/C T = 1224 MeV t = 0.72 0.01 2/dof = 30.0/40.0 200 GeV similar but T, b a bit

  11. When do soft processes no longer saturate the observed cross section? hydrodynamics-inspired fit of the data: From Schnedermann, et al. Phys. Rev. C48, 2462 (1993) Fit low pt part of the spectrum (mt –m0) < 1 GeV Compare to full hydro to verify functional form Extrapolate fit to see how soft processes extrapolate to higher pT

  12. Parameterization looks like hydro

  13. Extrapolate soft component using hydrodynamics nucl-ex/0307010 • Hydrodynamic flow modifies pt threshold where hard physics starts to dominate; species dependent! • physics is soft (thermal) until pt 3 GeV/c for h+ + h- Calculate spectra using hydro parameters h+ + h - =  p, K, p Compare sum to measured Charged particle pT spectrum

  14. How does freezeout vary with centrality? Peripheral collisions flow less, and have higher Tfo (they approach pp) But, does hydro make sense there?

  15. Almond shape overlap region in coordinate space Pressure? “elliptic flow” barometer 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

  16. v2 for p, K, p/pbar (value is large…) nucl-ex/0305013 p below p for pT < 2 GeV/c. Then crosses over Values ~ saturate at high pT  geometry? pT/quark seems ~ constant  create hadrons by coalescence of quarks from boosted distribution?

  17. v2 predicted by hydrodynamics, but… Kolb, et al. Hydro can reproduce magnitude of elliptic flow for p, p at low pT BUT must add QGP to hadronic EOS!! Similar conclusion reached by Ko, Kapusta, Bleicher, others… rescattering s must be very large!

  18. schematic view of jet production hadrons leading particle q q hadrons leading particle a unique probe for physics of hot medium Probe: Jets from hard scattered quarks Observed via fast leading particles or azimuthal correlations between the leading particles • But, before they create jets, the scattered quarks radiate energy (~ GeV/fm) in the colored medium • decreases their momentum (fewer high pT particles) • “kills” jet partner on other side • “jet quenching”

  19. AA AA If no “effects”: RAA < 1 in regime of soft physics RAA = 1 at high-pT where hard scattering dominates Suppression: RAA < 1 at high-pT AA Nuclear Modification of Hadron Spectra? 1. Compare Au+Au to nucleon-nucleon cross sections 2. Compare Au+Au central/peripheral Nuclear Modification Factor: nucleon-nucleon cross section <Nbinary>/sinelp+p

  20. Au-Au s = 200 GeV: high pT suppression! PRL91, 072301(2003) nucl-ex/0304022 Au-Au nucl-ex/0304022

  21. central nucl-ex/0308006 Suppression is also observed in inclusive charged Yield gradually decreases from peripheral to central collisions Inclusive RAA > p0 in pT range 2-4 GeV/c Periph.

  22. Suppression: a final state effect? Hadron gas • Hadronic absorption of fragments: • Gallmeister, et al. PRC67,044905(2003) • Fragments formed inside hadronic medium • Energy loss of partons in dense matter • Gyulassy, Wang, Vitev, Baier, Wiedemann… Absent in d+Au collisions! d+Au is the “control” experiment

  23. probe rest frame r/ ggg Suppression: an initial state effect? • Gluon Saturation • (color glass condensate) Wavefunction of low x gluons overlap; the self-coupling gluons fuse, saturating the density of gluons in the initial state.(gets Nch right!) • Initial state elastic scattering (Cronin effect) Wang, Kopeliovich, Levai, Accardi • Nuclear shadowing Levin, Ryshkin, Mueller, Qiu, Kharzeev, McLerran, Venugopalan, Balitsky, Kovchegov, Kovner, Iancu … RdAu~ 0.5 D.Kharzeev et al., hep-ph/0210033 Broaden pT :

  24. Centrality Dependence Au + Au Experiment d + Au Control • Dramatically different and opposite centrality evolution of AuAu experiment from dAu control. • Jet suppression is clearly a final state effect.

  25. Cronin effect in d+Au PRL91, 072303(2003) (h++h-)/2 Somewhat larger in the charged hadron measurement Larger effect in protons at mid pT ?? Implication of RdAu: RHIC at too high x for gluon saturation… p0

  26. To help sort out initial state effects d+Au PHENIX preliminary high pT Initial state multiple scattering mechanism? NOT incoherent soft multiple scatterings… low pT =n Mesons vs. baryons Cronin effect… Could help sort out fragmentation function vs. parton recombination

  27. Back-to-back jets observed in d+Au • observe no (big) • suppression in • back-to back jets! • probably is some jet • broadening due to initial • multiple scattering… PHENIX preliminary

  28. use pp to study parton kT, jet properties pp correlation function, even at intermediate pT range, dominated by jet fragments. The near angle peak width N intra-jet correlations The far angle peak width F inter-jet correlations PHENIX PRELIMINARY 1<pT=1.2<1.5 N=0.530.03 F=0.610.07 2.2<pT=2.8<6.0 N=0.250.01 F=0.490.04 Fit = const + Gauss(0)+Gauss()

  29. jet fragmentation  momentum |ky| = mean effective transverse momentum of the two colliding partons in the plane  to beam axis |jy| = mean transverse momentum of the hadron with respect to the jet axis (in the plane  to beam axis)

  30. charged hadrons in pp s = 200GeV At pT<2GeV the near angle peak width and|jTy| is reduced by “Seagull effect” see. e.g Phys.Lett.B320:411-416,1994 PHENIX preliminary |jTy| = 37316 MeV/c |kTy| = 72534 MeV/c PHENIX preliminary

  31. Jet cone “width” independent of s * *Subject to same trigger bias by selecting pT of particles CCOR Collaboration Phys. Lett. 97B(1980)163

  32. AuAu h correlation 2.2<pT<5.0 GeV/c pp AuAu Fit  (1+2 v22 cos(2)) + const [Gauss( =0,N)+YF/YNGauss( =, F)] + const v22determined from the fit N, F,YF=gauss(0) / YN= gauss()fixed values taken from pp centrality: 50-90% centrality: 0-10% PHENIX PRELIMINARY PHENIX PRELIMINARY Flow and jet part can be clearly separated. Fit forces v2 0, it indicates the lack of back-to-back correlation

  33. Correlation width Charged hadron correlations - small Df • Now fit v2 + Gaussian, let N float: PHENIX PRELIMINARY The dashed line corresponds to the |jTy| = 400 MeV/c There is no significant broadening observed. Trigger bias? Collinear radiation inside jet cone? Jet fragmentation outside the QCD medium?

  34. central Au+Au is very baryon rich! nucl-ex/0305036 (PRL) p/ ~1 at high pT in central collisions Higher than in p+p or jets in e+e- collisions pQCD spectrum shifted by 2.2 GeV Hydro. expansion at low pT + jet quenching at high pT: Recombination of boosted q’s? Medium modified fragmentation function? Teff = 350 MeV

  35. Do the baryons scale with Ncoll? Au+Au central peripheral Baryon yields not suppresed  Ncoll at pT = 2 – 4 GeV/c hard/soft process interplay… Quark recombination? Medium modification of fragmentation function?

  36. Deconfinement? Does colored medium screen c+cbar? 0-20% most central Ncoll=779 40-90% least central Ncoll=45 20-40% semi central Ncoll=296 Look at J/Y nucl-ex/0305030 R.L. Thews, M. Schroedter, J. Rafelski Phys. Rev. C63 054905 (2001): Plasma coalesence model for T=400MeV and ycharm=1.0,2.0, 3.0 and 4.0. L. Grandchamp, R. RappNucl. Phys. A&09, 415 (2002) and Phys. Lett. B 523, 50 (2001): Nuclear Absorption+ absoption in a high temperature quark gluon plasma A. Andronic et. Al. Nucl-th/0303036 Proton Don’t know yet about deconfinement, but don’t see EXTRA (thermal) J/Y

  37. J/y in pp collisions hep-ex/0307019 <pT> = 1.80 ± 0.23 (stat) ± 0.16 (sys) GeV  = 3.99 ± 0.61 (stat) ± 0.58 (sys) ± 0.40 (abs) mb

  38. Grows with s as expected

  39. scharm by single e production 130 GeV/A Au+Au Cross section fits into expected energy dependence Phys.Rev.Lett. 88 (2002) 192303

  40. Centrality dependence of open charm in Au+Au central Compare to (PYTHIA) an event generator tuned for pp collisions… no large suppression- unlike light quarks! peripheral Spectra of electrons from c e + anything photonic sources are subtracted

  41. 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

  42. conclusions • Rapid equilibration! • Strong pressure gradients, hydrodynamics works • Constituent scattering cross section is very large • EOS is not hadronic • The hot matter is “sticky” – it absorbs energy & seems to • transport it efficiently • Seeenergy loss, disappearance of back-to-back jets • d+Au data says: final state, not initial state effect • So, the stuff is dense, hot, ~ equilibrated AND NEW! • QGP discovery? • J/Y suppression or not? Next run • Tinitial? direct photon analysis underway • Properties not as expect for plasma – a gluon liquid?

  43. Why a liquid? • Mean free path is very short • Smaller than size of system • Must be so to get large energy loss • Interaction among gluons is quite strong • Have a (residual) correlation among partons until T>>Tc

  44. A couple of mysteries…

  45. Hydro describes single + multi-particles But FAILS to reproduce two-particle correlations! • How to increase R without increasing Rout/Rside??? • EOS? • initial T & rprofiles? • emissivity? • Maybe an experimental artifact (i.e. Coulomb corrections) ?

  46. Rside Rout Rlong λ Need partial Coulomb correction? Halo • Long-lived resonance contribution • Full Coulomb correction on all pion pairs assuming well localized (core) source ~5fm. • pions from resonance decays come from a larger “halo” source, and have weaker (negligible) Coulomb effect. Core • fPC dependence of Bertsch-Pratt radii • Vary the fraction (fPC) of Coulomb corrected pairs from 0 (no Coulomb) to 1 (full Coulomb). • Rside and Rlong decrease as fPC is reduced. • In contrast, Rout increase as fPC is reduced. • The ratio Rout/Rside is very sensitive to fPC . R [fm], λ (x10) No Coulomb Full Coulomb 0 0.2 0.4 0.6 0.8 1.0 fPC

  47. Comparison of kaon to pion In the most 30% central

  48. kT dependence of R Centrality is in top 30% • Broad <kT> range : 0.2 - 1.2 GeV/c • All R parameters decrease as a function of kT •  consistent with collective expansion picture. • Stronger kT dependent in Rlong have been observed. kT : average momentum of pair

  49. kT dependence of Rout/Rside A. Enikizono QM2002 C.M. Kuo, QM2002 poster (PHOBOS) 200 GeV: @0.25 GeV/c

  50. n ZDC p Neutron tagged events enhance peripheral collisions Forward n tagged d+Au <Ncoll> = 5.0 / 3.6 Could be Ncoll dependence d+Au looks very similar to p+Au

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