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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 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/Ψsuppression • Jet quenching • Thermal QGP radiation • Dilepton enhancement • Quark recombination • Enhancement of fluctuations …
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?
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
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
SPS e+e- collisions Experimental results Strangeness enh. 1 Strangeness enhancement 2 Schwinger mechanism
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?
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 ?
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”
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)
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
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
Medium Induced Radiation Clearly similar Recursion Method is needed to go toward a large number of scatterings! Ivan Vitev,LANL
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
Energy Loss and expanding QGP Probe the density In the transverse plane Quenching is angle dependent
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
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.
Is the plasma a QCD-QGP? • Consistent with L2 non-abelian plasma behavior • Consistent with e ~ 10 GeV (similar to hydro)
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
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 …
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
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
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
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!
Baryon/Meson ratio Be careful , there are mass effects ! • Resonance decays (r-> p p) • Shrinking of baryon phase space Fragmentation not included for L
Elliptic Flow from Coalescence Wave function effects -> scaling breaking 10% q/m 5% b/m wave function effect Coalescence scaling Enhancement of partonic v2
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
~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 …
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 !?
J/Ysuppression m + m- 6% cc bound state, MY= 3.1 GeV e+e- 6% Charm Thermalize in the plasma
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
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
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
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]
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]
dominated by regeneration • sensitive to: • mc* , open-charm degeneracy Charmonia in URHIC’s RHIC SPS
Does Charm quark thermalize? • pT Spectra and Yield of D and/or J/Y • v2 of D meson (single e) From hard pp collision
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
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
AMPT, L.W. Chen, C.M. Ko, nucl-th 0409058 Similar to the cross section needed in the light sector !
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
Result for V channel (J/y) A(w)=w2r (w) J/y (p = 0) disappears between 1.62Tc and 1.70Tc
Result for PS channel (hc) A(w)=w2r (w) hc (p =0) also disappears between 1.62Tc and 1.70Tc
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
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
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!
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 !