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Probing the Quark Gluon Plasma

Probing the Quark Gluon Plasma. What sort of plasma is a QGP? RHIC and its experiments Collective flow Transmission of color-charged probes Transport properties and hadronization Conclusions. Barbara Jacak Stony Brook May 18, 2005. reminder: what’s a plasma?.

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Probing the Quark Gluon Plasma

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  1. Probing the Quark Gluon Plasma • What sort of plasma is a QGP? • RHIC and its experiments • Collective flow • Transmission of color-charged probes • Transport properties and hadronization • Conclusions Barbara Jacak Stony Brook May 18, 2005

  2. reminder: what’s a plasma? • 4th state of matter (after solid, liquid and gas) • a plasma is: • ionized gas which is macroscopically neutral • exhibits collective effects • interactions among charges of multiple particles • spreads charge out into characteristic (Debye) length, lD • multiple particles inside this length • “normal” plasmas are electromagnetic • quark-gluon plasma interacts via strong interaction • color forces rather than EM • exchanged particles: g instead of g

  3. Map of high energy densities

  4. Plasma coupling parameter? • For high gluon density achieved at RHIC & LHC • estimate G = <PE>/<KE> • using QCD coupling strength, g • <PE>=g2/d d ~1/(41/3T) • <KE> ~ 3T • g2 ~ 4-6 (value runs with T) • G ~ g2 (41/3T)/ 3T  so plasma parameter G ~ 3 • NB: such plasmas known to behave as a liquid! • Correlated or bound q,g states, but not color neutral • So the quark gluon plasma is a strongly coupled plasma • As in warm, dense plasma at lower (but still high) T

  5. from S. Ichimaru

  6. Properties of interest: • How do these plasmas transport energy? • How quickly can they equilibrate? • What is their viscosity? G >10 can even be crystalline! • How much are the charges screened? • Is there evidence of plasma instabilities at RHIC? • Can we detect waves in this new kind of plasma? novel plasma of strong interaction Other strongly coupled plasmas • Inside white dwarfs, giant planets, and neutron stars • (n star core may even contain QGP) • In ionized gases subjected to very high pressures, magnetic fields, or particle interactions • Dusty plasmas in interplanetary space & planetary rings • Solids blasted by a laser

  7. quarks & gluons retain correlations, medium exhibits liquid properties NB: the (quasi-)bound states are not your mother’s hadrons! take a deep breath… • What did we expect for QGP? • What SHOULD we expect? weakly interacting gas of quarks & gluons

  8. Plasma Diagnostics • Many interesting systems are short-lived! • ns for laser-heated plasmas • study via time integrated observables • (radiation or probes) • plasma folks can also measure time dependence • correlations of probes and/or medium particles • Transmission of external probes • hard x-rays, electrons. In our case: jets • Final state cluster distributions for early state info • Diagnostic of collective motions • Multiparticle emission • Single particles in multiparticle field, acoustic waves

  9. Method using 3 lasers: 1) create shock, 2) x-rays, and 3) probe sample 1) Shock generating laser 3) Probe laser 2) x-ray generating laser R. Lee, S. Libby, LLNL; RBRC workshop

  10. Shock and interface trajectories are measured by x-ray radiography • Slope of shock front yields Us • Slope of pusher interface gives Up streak camera record R. Lee, S. Libby, LLNL P-P0=r0UsUp

  11. We use RHIC at Brookhaven National Laboratory s = 200 GeV/A Au+Au, p+p and d+A to compare

  12. STAR 4 complementary experiments

  13. z y x Almond shape overlap region in coordinate space Collective motion? Pressure: a barometer called “elliptic flow” Origin: spatial anisotropy of the system when created multiple scattering of particles builds pressure  collective expansion spatial anisotropy  momentum anisotropy dN/df ~ 1 + 2 v2(pT) cos (2f) + …

  14. The data show c.m. beam energy Anisotropy amplitude grows with beam energy, then flattens. For LHC first guess – use same v2 at same pT

  15. Hydro. Calculations Huovinen, P. Kolb, U. Heinz Kolb, et al Hydrodynamics can reproduce magnitude of elliptic flow for p, p. BUT mass dependence → softer than hadronic EOS!! NB: these calculations have viscosity = 0 medium behaves as an ideal liquid v2 reproduced by hydrodynamics • see large pressure buildup! • anisotropy  happens fast • early equilibration STAR PRL 86 (2001) 402 central

  16. gas of strongly interacting Li atoms • M. Gehm, S. Granade, S. Hemmer, K, O’Hara, J. Thomas Science 298 2179 (2002) • excite Feshbach resonance: 38th vibrational • Li2 state → 0 energy, huge cross section strongly coupled weakly coupled

  17. proton pion Caveat: use hydrodynamic models carefully nucl-ex/0410003 Hydro models: Teaney (w/ & w/o RQMD) Hirano (3d) Kolb Huovinen (w/& w/o QGP)

  18. v2 scales ~ with # of quarks! • evidence that quarks are the particles when the pressure is built up • pattern same at LHC?? WHICH are the flowing degrees of freedom? v2 for particles of different mass

  19. flow and thermalization • Data suggest that partons are what flows • quark scaling of v2 • requirement of QGP EOS for hydro to reproduce v2 • Look “under the hood” in the hydro calculation • v2 magnitude → start hydro by t = 0.6 fm/c (U. Heinz) • technique exactly the same in plasma physics • HOW does the system thermalize so fast? • collisions? quasi-bound states increase s • plasma instabilities? maybe (Arnold, et al; Rebhan …) • help to constrain the imagination • do heavy quarks thermalize and flow? • use massive quarks to probe diffusion in QGP • D ~ tcoll ; small diffusion → large elliptic flow & Eloss

  20. Heavy quark flow? nucl-ex/0502009 PHENIX measures v2 of non-photonic e± electron ID in Au+Au via RICH + EMCAL measure and subtract photonic sources using converter YES v2≠ 0 at 90% C.L. data consistent with heavy q thermalization “predicted” by Moore&Teaney hep-ph/0412346 *run4 analysis now Greco,Ko,Rapp. PLB595, 202 (2004) LHC: CGC initial state, even greater pT reach

  21. 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

  22. Produced pions Produced photons 1st: benchmark the probes in p+p collisions • calculable with perturbative QCD!

  23. Direct Photon Spectra in Au+Au • g does not interact with the color charges • data and theory agree → calibrated probe • pQCD works in the complex environment of two Au nuclei colliding • g/p0 large, making g easier to measure!

  24. peripheral Ncoll = 12.3  4.0 central Ncoll = 975  94 strongly interacting probe: a different story!

  25. Photons shine, Pions don’t

  26. 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

  27. Could suppression be an initial state effect? Au + Au Experiment d + Au Control PHENIX preliminary • Dramatically different and opposite centrality evolution of AuAu experiment from dAu control. • Jet Suppression is clearly a final state effect.

  28. Pedestal&flow subtracted Are back-to-back jets there in d+Au? Yes! importance of “p”+A comparison push hard for it at LHC!

  29. Induced gluon brehmsstrahlung pQCD (Vitev): energy loss 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

  30. So, what do E loss & collectivity tell us? • Medium is opaque to colored probes • Thermalization must be very fast (< 1fm/c) • Hydrodynamic, energy loss models constrained with data:

  31. Charm via single e± in p+p PHENIX preliminary s exceeds NLO and phenomenological predictions by how much? a bit controversial. I think factor 2-3. please measure scc in p+p at LHC too!!

  32. p+p single e± as reference for Au+Au → RAA RAA energy loss of charm quarks! Eloss + flow → small diffusion coeff  short time btwn charm collisions (NB likely some e± from B decays) pT (GeV/c)

  33. RAA pT (GeV/c) Is Eloss consistent with that of light quarks? non-pert. effects on “normal” g radiation calculation from: Dainese, Armesto, Wiedemann data say: same transport coefficient, smaller hadron suppression q consistent w/ light quark eloss

  34. What is going on? • The objects colliding inside the plasma are not baryons and mesons • The objects colliding also do not seem to be quarks and gluons totally free of the influence of their neighbors • The cross section of early q,g collisions must be ~50 times larger than those of free q,g for large v2 • Quarks and gluons are interacting, but need not be locally (color) neutral like the baryons & mesons. Neutrality scale likely larger, as expected for a plasma.

  35. And expect hard-soft recombination C.M. Ko et al, Hwa & Yang PRC68, 034904, 2003 PRC67, 034902, 2003 nucl-th/0401001 & 0403072 Study jet fragmentation to probe medium properties Radiated gluons are collinear (inside jet cone) Can also expect a jet “wake” effect, medium particles “kicked” alongside the jet by energy they absorb Fries, Bass & Mueller nucl-th/0407102

  36. correlation functions of two high pT hadrons Elliptic flow component measured vs. BBC reaction plane

  37. decompose to get jet pair distribution Away-side jets broadened non-Gaussian! ~2sdip at p& peak at 1.25 rad around hard parton thru medium integrating entire away side recovers jet partners Casalderry, Shuryak, Teaney say 1.1 rad cone hep-ph/0411315

  38. interpretation? *it’s fun to speculate • pQCD energy loss is by gluon radiation • mostly collinear with radiating particle • various authors now remind us of ionization • (Shuryak, Vitev …) • more direct interaction of probe parton with medium! • drives question “what happens to the lost energy” • options: • it remains collinear • creates a wake in the medium (Fries et al; Shuryak) • thermalizes in the medium • speed of wake reflects cs in the medium: cosfm=cs/c • = 1/√3 in non-interacting QGP, ~ 0.45 in hadron gas • = 1/3 a mixture of the two??

  39. Recall the annoying baryon puzzle… PRELIMINARY h/p0 ratio shows baryons enhanced for pT < 5 GeV/c

  40. identify triggers, count partners nucl-ex/0408007 trigger: 2.5-4 GeV/c; partner 1.7-1.5 Jet partner likely for trigger baryons as well as mesons! Same side: slight decrease with centrality for baryons Dilution from boosted thermal p, pbar? • hadron formation time • (lab frame) tf ~ Rh (Eh/mh) • for 2.5 GeV pT; Rh~1 fm • tf ~ 9-18 fm/c for pions ~ 2.7 fm/c for baryons Baryons formed inside! • pick up q from wake?

  41. RHIC How about the screening length? • J/Y • Test confinement: • do bound c + c survive? • or does QGP screening kill them? • Suppression was reported in lower • energy heavy ion collisions at CERN currently being analyzed; first look not conclusive

  42. 0-20% most central Ncoll=779 40-90% most central Ncoll=45 20-40% most central Ncoll=296 Cu+Cu, 2005 run South Muon Arm 6062+/-195 J/Y, 343+/-82 Y’ (6%) data on Au+Au, Cu+Cu being analyzed

  43. so, is there QGP at RHIC? Yes! RHIC creates a strongly coupled, opaque liquid energy density & equation of state not hadronic! must search for plasma phenomena, not asymptotic freedom • With aid of hydrodynamics, l-QCD and p-QCD models: • e ~ 15 GeV/fm3 • dNgluon/dy ~ 1000 • sint large for T < 2-3 Tc • Are measuring properties of this new kind of plasma • opacity, collision frequency, EOS, screening • speed of sound? • color and maybe thermal conductivity to be quantified • color screening currently being analyzed • LHC will make QGP too. (As) strongly coupled? • higher s, pT reach for hard probes; soft physics at higher T

  44. RBRC workshop on Dec.16, 17 2004 Thanks for support from RBRC & NSF! Strongly Coupled Plasmas: Electromagnetic, Nuclear and Atomic organizers: B. Jacak, S. Bass, E. Shuryak, T. Hallman, R. Davidson An interdisciplinary “experiment” opportunity to learn from each other form new collaborations/directions http://quark.phy.bnl.gov/~bass/workshop.htm for program, slides

  45. 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!) • Multiple elastic scatterings (Cronin effect) Wang, Kopeliovich, Levai, Accardi Levin, Ryshkin, Mueller, Qiu, Kharzeev, McLerran, Venugopalan, Balitsky, Kovchegov, Kovner, Iancu … RdAu~ 0.5 D.Kharzeev et al., hep-ph/0210033 Broaden pT :

  46. d+Au central/peripheral PTH = Punch Through HadronsHDM = Hadronic Decay Muon 1.5 < pT (GeV/c) < 4.0 PHENIX nucl-ex/0411054 x~0.2-0.3 d Au Au x~0.2x10-3 Suppression at forward η and enhancement in the back η.

  47. Compare with BRAHMS nucl-ex/0411054 Overall consistent.

  48. Color glass condensate? Kharzeev, hep-ph/0405045 Hadron Punch Through Centrality, pT dependence ~ correct Slightly better agreement with BRAHMS data “normal” shadowing cannot explain (R. Vogt hep-ph/0405060) …could be sign of CGC

  49. But, recombination lurks… Hwa, Yang and Fries nucl-th/0410111 • shower + medium recombination → reductes soft parton density on deuteron side • Can explain fward-bward asymmetry AND RCP (protons) > RCP (mesons) at midrapidity. BRAHMS data

  50. From talk of Todd Ditmire (U. Texas) Diagnostic quantity measured Transmission of g, hard x-rays density, atomic properties Probe photon interference imaging, expansion velocity Phase shifts of probe photon release velocity of expanding material x-ray reflectivity image shock front spectrum, time structure of hydrodynamic expansion radiated clusters Time-resolved absorption density profile with time Electron radiation plasma oscillations test hydro predictions Anisotropy in radiation test calculations of field gradients

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