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Search for the Quark-Gluon Plasma in Heavy Ion Collision

Search for the Quark-Gluon Plasma in Heavy Ion Collision. V. Greco. Outline II. Probes of QGP in HIC What we have find till now! strangeness enhancement jet quenching coalescence J/ Y suppression. What we have learned ?. Probes of QGP. Strangeness enhancement J/ Ψ suppression

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Search for the Quark-Gluon Plasma in Heavy Ion Collision

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  1. Search for the Quark-Gluon Plasma in Heavy Ion Collision V. Greco

  2. Outline II • Probes of QGP in HIC • What we have find till now! • strangeness enhancement • jet quenching • coalescence • J/Y suppression • What we have learned • ?

  3. Probes of QGP • Strangeness enhancement • J/Ψsuppression • Jet quenching • Thermal QGP radiation • Dilepton enhancement • Quark recombination • Enhancement of fluctuations …

  4. Hadronic channels: Strangeness Enhancement • Basic Idea: • Production threshold is lowered by the chiral restoration In the QGP: • Equilibration timescale ? How much time do you have?

  5. QGP Scenario Hadronic Scenario Decreasing threshold in a Resonance Gas To be weighted with the abundances npQCD calculation with quasi particle picture and hard-thermal loop Still give t~5-10 fm/c

  6. How one calculates the Equilibration Time Similarly in hadronic case but more channels Reaction dominate by gg 6 fm/c • (pQCD) Equilibration time in QGP teq ~10 fm/c > tQGP • Hadronic matter teq ~ 20-30 fm/c

  7. SPS e+e- collisions Experimental results Strangeness enh. 1 Strangeness enhancement 2 Schwinger mechanism

  8. Present Knoweldge • AGS (6GeV) explained by hadronic models • Enhancement at SPS and RHIC (8.8 GeV-200 GeV) - not explained by hadronic models - unless chiral symmetry effects are modelled • Enh. Agrees with statistical models in grand-canonical ensemble - no canonical suppression Present Unknoweldge • What means the absence of canonical suppression? - multiparticle dynamics in QGP - higher cross section respect to pQCD • Enh. is more a signal of chiral restoration already in dense hadronic matter? • Why Enh. Larger at SPS than at RHIC?

  9. Jet quenching Decrease of mini-jet hadrons (pT> 2 GeV) yield, because of in medium radiation. Ok, what is a mini-jet? why it is quenched ?

  10. High pT Particle Production hadrons Parton Distribution Functions hadrons Hard-scattering cross-section leading particle Fragmentation Function High pT (> 2.0 GeV/c) hadron production in pp collisions ~ Jet: A localized collection of hadrons which come from a fragmenting parton c a Parton Distribution Functions Hard-scattering cross-section Fragmentation Function b d phad= zpc, z<1 energy needed to create quarks from vacuum “Collinear factorization”

  11. Jet Fragmentation-factorization p, K, p ... c b a A B d ph= zpc, z<1 energy needed to create quarks from vacuum AB= pp (e+e-) a,b,c,d= g,u,d,s…. Parton distribution after pp collision p/p < 0.2 B.A. Kniehl et al., NPB 582 (00) 514 (+ phenomenological kT smearing due to vacuum radiation)

  12. High pT Particle Production in A+A Parton Distribution Functions Intrinsic kT , Cronin Effect Shadowing, EMC Effect Hard-scattering cross-section c a Partonic Energy Loss b d hadrons Fragmentation Function leading particle suppressed Known from pp and pA

  13. Energy Loss ~ Brehmstralung radiation in QED Color makes a difference pi pf × × k pi pf thickness pi pf Non-Abelian gauge c k a × Gluon multiple scattering Static scattering centers assumed Gauge invariance O(1/E2) Transport coefficient

  14. Medium Induced Radiation Clearly similar Recursion Method is needed to go toward a large number of scatterings! Ivan Vitev,LANL

  15. Jet Quenching Quenching Jet distribution Large radiative energy loss in a QGP medium L/l opacity DE/E ~ 0.5 Non – abelian energy loss weak pT dependence of quenching

  16. Energy Loss and expanding QGP Probe the density In the transverse plane Quenching is angle dependent

  17. How to measure the quenching Self-Analyzing (High pT) Probes of the Matter at RHIC Nuclear Modification Factor: nucleon-nucleon cross section <Ncoll> AA If R = 1 here, nothing new going on

  18. 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.

  19. Is the plasma a QCD-QGP? • Consistent with L2 non-abelian plasma behavior • Consistent with e ~ 10 GeV (similar to hydro)

  20. Baryon-Meson Puzzle protons PHENIX,nucl-ex/0212014 • Fragmentation p/p ~ 0.1-0.2 • Jet quenching should affect both Fragmentation is not the dominant mechanism of hadronization at pT ~ 1-5 GeV !? pions PHENIX, nucl-ex/0304022 p0 suppression: evidence of jet quenching before fragmentation

  21. Coalescence vs. Fragmentation Fragmentation: • Leading parton pT ph= z pT according toa probability Dh(z) • z < 1, energy needed to create quarks • from vacuum Parton spectrum Coalescence: • partons are already there $ to be close in phase space $ • ph= n pT ,, n= 2,3 baryons from lower momenta BM Even if eventually Fragm. takes over …

  22. Coalescence Our implementation npQCD |Mqq->m|2 depends only on the phase space weighted by wave function (npQCD also encoded in the quark masses , mq=0.3 GeV, ms=0.475 GeV) • Energy not conserved • No confinement constraint

  23. Coalescence Formula fqinvariant parton distribution functionthermal (mq=0.3 GeV, ms=0.47 GeV) with radial flow (b=0.5) + quenched minijets (L/l=3.5) fHhadron Wigner function Dx = 1/Dp coalescence radius In the rest frame

  24. T=170 MeV ET ~ 700 GeV b(r)~ 0.5 r/R T ~ 170 MeV quenched soft hard V ~ 900 fm-3 (e ~ 0.8 GeVfm-3) L/l=3.5 P. Levai et al., NPA698(02)631 Distribution Function Hadron from coalescence may follow jet structure (away suppr.) REALITY: one spectrum with correlation kept also at pT < 2 GeV

  25. Pion & Proton spectra Au+Au @200AGeV (central) V. Greco et al., PRL90 (03)202302 PRC68(03) 034904 R. Fries et al., PRL90(03)202303 PRC68(03)44902 R. C. Hwa et al., PRC66(02)025205 • Proton suppression hidden by coalescence!

  26. Baryon/Meson ratio Be careful , there are mass effects ! • Resonance decays (r-> p p) • Shrinking of baryon phase space Fragmentation not included for L

  27. Elliptic Flow from Coalescence Wave function effects -> scaling breaking 10% q/m 5% b/m wave function effect Coalescence scaling Enhancement of partonic v2

  28. Effect of Resonances on Elliptic Flow Pions from resonances w.f. + resonance decay K & p * K, L, p …v2 not affected by resonances! p coal. moved towards p data nucl-th/0402020

  29. ~8% trigger Assoc. Back-to-Back Correlation quenched Trigger is a particle at 4 GeV < pTrig < 6 GeV Away Side: quenching has di-jet structure Same Side: Indep. Fragm. equal (?!) to pp Associated is a particle at 2 GeV < pT < pTrig Coalescence with s-h with away side suppressed, but same side is reduced if no futher correlation …

  30. What was not emphasized IAA ~ 1 peak like in pp IAA > 1 against the … • how explain p/p ratio, • v2B/v2M ? • at lower pT correlation • increase !?

  31. J/Ysuppression m + m- 6% cc bound state, MY= 3.1 GeV e+e- 6% Charm Thermalize in the plasma

  32. q q q,q,g distribution modified Coulomb -> Yukawa s =0 doesn’t mean no bound ! J/Ysuppression • In a QGP enviroment: • Color charge is subject to screening of the medium • -> qq interaction is weakened • Linear string term vanish in the confined phase • s(T) -> 0 deconfinement T ~ 4 Tc T ~ Tc

  33. Suppression respect to extrapolation from pp J/Y Initial production Dissociation In the plasma Recombine with light quarks • Associated suppression of charmonium resonances Y’, cc , … as a “thermometer”, like spectral lines for stellar interiors • B quark in similar condition at RHIC as Charmonium at SPS

  34. NUCLEAR ABSORBTION • pre-equilibrium cc formation time and • absorption by co-moving hadrons • HADRONIC ABSORBTION • re-scattering after QGP formation • DYNAMICAL SUPPRESSION • (time scale, g+J/Y-> cc,…) pA ( & models) sabs ~ 6 mb W. Liu

  35. Dynamical dissociation J/y + g c + c + X Fireball dynamical evolution regeneration Life-time gluon-dissociation, inefficient for my≈ 2 mc* “quasifree” dissoc. [Grandchamp ’01]

  36. If c-quarks thermalize: RHIC SPS Regenerationin QGP / atTc J/y + g c + c + X - → ← • RHIC central: Ncc≈10-20, • QCD lattice: J/y’s to~2Tc [Grandchamp +Rapp ’03]

  37. dominated by regeneration • sensitive to: • mc* , open-charm degeneracy Charmonia in URHIC’s RHIC SPS

  38. Does Charm quark thermalize? • pT Spectra and Yield of D and/or J/Y • v2 of D meson (single e) From hard pp collision

  39. S. Batsouli,PLB557 (03) 26 V. Greco , PLB595 (04) 202 D mesons D mesons Pythia B mesons Hydro No B mes. D meson spectra Single electron does not resolve the two scenarios Elliptic flow better probe of interaction

  40. Charmed Elliptic Flow V2q from p, p, K, L Flow mass effect Coalescence can predict v2D for v2c = 0 &v2c = v2q S. Kelly,QM04 Quenching V2 of electrons VGCMKRR, PLB595 (04) 202

  41. AMPT, L.W. Chen, C.M. Ko, nucl-th 0409058 Similar to the cross section needed in the light sector !

  42. Hydrodynamics describe well the bulk of the matter • Transport codes needs a quite large npQCD cross section • Charm quark strongly interact with the plasma • Recent lattice QCD find bound states of cc and qq at T>Tc Rethinking the QGP at Tc < T < 2Tc “Strong” QGP Quark gluon plasma was predicted to be a weakly interacting gas of quarks and gluons • The matter created is not a firework of multiple minijets • Strong Collective phenomena

  43. Result for V channel (J/y) A(w)=w2r (w) J/y (p = 0) disappears between 1.62Tc and 1.70Tc

  44. Result for PS channel (hc) A(w)=w2r (w) hc (p =0) also disappears between 1.62Tc and 1.70Tc

  45. Sketch of “Strong” QGP The elementary excitation are not free gluons and quarks, but hadronic excitations with strongly modified “in-medium” properties and with chirally restored phase • Loosely bound states crucial for particle • scattering • -> large cross section (Breit-Wigner ) • One has also to reproduce lattice EOS

  46. In Conclusion • Matter with energy density too high for simple hadronic • phase ( e > ec from lattice) • Matter is with good approximation thermalized (T >Tc ) • Jet quenching consistent with the hot and dense medium • described by the hydro approach • Hadrons seem to have typical features of recombination • Strangeness consistent with grand canonical ensemble • J/y ... Needed : - Thermal spectrum - Dilepton enhancement

  47. Bang Big Bang • e. m. decouple (T~ 1eV , t ~ 3.105 ys) • “thermal freeze-out “ • but matter opaque to e.m. radiation • Atomic nuclei (T~100 KeV, t ~200s) • “chemical freeze-out” • Hadronization (T~ 0.2 GeV, t~ 10-2s) • Quark and gluons We’ll never see what happened t < 3 .105 ys (hidden behind the curtain of the cosmic microwave background) HIC can do it!

  48. Bound state solution Screening Effect • Abelian • Non Abelian • (gauge boson self-interaction) One loop pQCD TBound is not Tc ! In HIC at √s ~ SPS J/Yshould be supressed !

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