The Flavors of the Quark-Gluon Plasma

Transcription

1 The Flavors of the Quark-Gluon Plasma Berndt Mueller SQM October 6-10, 2008

2 The QGP is a strange state of matter 2

3 QCD phase diagram T Quark- Gluon Critical end point? Plasma Strange quarks play crucial role in shaping the QCD phase diagram: Location of critical point(s) Stability of neutron stars Structure of CSC phase Hadronic matter Chiral symmetry broken 1 st order line U(1) A critical end point? Chiral symmetry restored Color superconductor Nuclei Neutron stars µ B 3

4 QGP & quark flavor quark-gluon plasma s, c, and b quarks are important probes of hadronic matter: - they are hard to produce (s below Tc ; c and b above Tc) Melting nuclear matter nucleons + mesons - quark flavor conserved under strong interactions c and b are also hard probes, i. e. their production can be reliably calculated in pqcd. 4

5 Color screening Induced color density φ a Static color charge (heavy quark) generates screened potential 5

6 Quark masses Higgs quark field Quark quark Heat melts the quark condensate: QCD mass disappears above T c. (Partial) chiral symmetry restoration condensate 6

7 Confinement The mechanism behind quark confinement in the vacuum is still not well understood, but it is quantitatively described by lattice QCD. Quark confinement above Tc disappears due to color screening. Effective description of quark confinement and the deconfinement transition exists: Polyakov loop model (P-NJL). L r = P exp ( ig β 0 dτa b 4 (x, τ) λb r 2 ) P-loop average projects color rep s. 3 = N 1 ( c tr L ) 3 = 1 ( 3 eiφ 1 + eiφ 2 + e i(φ 1 φ 2 ) ) tr L = 0 Confinement tr L = 1 Deconfinement Interplay between P-loop and quark condensate explains coincidence of Tc for deconfinement and chiral symmetry restoration. 7

8 PNJL phenomenology Fukushima; Roessner, Ratti, Weise;... 8

9 Strangeness enhanced The original idea (Rafelski): N(s ) N(q) = 1 2 m s T 2 K 2 ( m s / T )e µ B /(3T ) = 1 5 We almost always have more s than u or d quarks. When quark matter reassembles into hadrons, some of the numerous s quarks may, instead of being bound into kaons, form multiply Λ, Ξ, Ω strange antibaryons, such as. gg ss is essential for rapid strangeness equilibration! (JR & BM) Almost 30 years of investigation: The liberation of quark and gluon degrees of freedom (not necessarily thermalization) is required for strangeness equilibration. 9

10 s-enhancement at RHIC (sss) (qss) (qqs) STAR STAR 10

11 s-production revisited 3-flavor PNJL model (Fukushima): f q (k) = l 3 λ + +2 l 3 λ λ l 3 λ + +3 l 3 λ λ 3 + f q (k) = l 3 λ +2 l 3 λ 2 + λ l 3 λ +3 l 3 λ 2 + λ 3 qq Hung-Ming Tsai ss with λ ± = exp[ (E(k) µ)/t ] l 8 4/9 l 3 f g (k) = 1 8 n=1 tr L n 8 e n k /T A q = 1 2 A g = 1 2 4m 2 s 4m 2 s dss dss δ 1 4m2 q s δ ( s (k 1 + k 2 ) 2) σ q q s s (s) ( s (k 1 + k 2 ) 2) σ gg s s (s) d 3 k 1 (2π) 3 E(k 1 ) d 3 k 1 (2π) 3 k 1 d 3 k 2 (2π) 3 E(k 2 ) (2 36)f q(k 1 )f q (k 2 ) d 3 k 2 (2π) 3 k 2 ( )f g(k 1 )f g (k 2 ) 11

12 Parton distributions / f FD f q Ratio of quark distribitions functions for µ=0.1 GeV Quarks T=0.3 GeV T=0.2 GeV T=0.18 GeV T = 300 MeV T = 200 MeV / f BE f g Ratio of gluon distribitions functions Hung-Ming Tsai Gluons T=0.3 GeV T=0.2 GeV T=0.18 GeV T = 300 MeV 0.2 T = 180 MeV 0.2 T = 200 MeV T = 180 MeV k (GeV) k (GeV) f i ( k;p) T / f ( i k) Gluons more strongly suppressed near Tc than quarks, in spite of additional mechanism for quarks (χsb). 12

13 ss rate in PNJL model Hung-Ming Tsai gg ss qq ss dominates q and g disappear, hadrons dominate (hadronic rates calculable in, e.g.: (P)NJL model; UrQMD, JAM) 13

14 Hadro-Chemistry 14

15 Chemical equilibrium γ s / γ q = 1.00 ± 0.01 Sudden hadronization from deconfined state? 15

16 Statistical model Particle/antiparticle yield: Baryons, e.g., Λ = (uds): Y ± i (p) = γ i exp E (p) µ i i T γ Λ = γ q 2 γ s, µ Λ = 2µ q + µ s Mesons, e.g., K - = (sū): γ K = γ s γ q, µ K = µ s µ q γ s / γ q = 1 γ s,γ q > 1 implies relative equilibration of strange quarks. implies over-abundance of baryons. RHIC data: γs = γq = 1 for Tch MeV; or: γs > γq > 1 for Tch 140 MeV. 16

17 Out of equilibrium Quality of data on identified hadrons and even resonances suggests that a comprehensive assessment of the interplay between dynamical hadronization and final-state hadron chemical reactions is timely. It is well known that particle number changing reactions incrementally cease as the hadron gas expands and cools, and γs,γq become greater than 1, even if γs = γq =1 at hadronization: Chemical equilibrium at Tf,kin 100 MeV underpredicts protons and antiprotons by factor 3! Theoretical tools (e.g. UrQMD or JAM cascades following hadronization) exist to study the implications of any conceivable hadronization scenario. Systematic comparisons of different scenarios in light of the RHIC (and SPS, and soon LHC) data is missing. Opportunity for Theory-Experiment collaboration. 17

18 v 2 (p T ) hadronization Failure of ideal hydrodynamics tells us how hadrons form: New at RHIC! Mass splitting characteristic property of hydrodynamics 18

19 Quark number scaling of v 2 In the recombination regime, meson and baryon v 2 can be obtained from the quark v 2 : v 2 M ( p ) q T = 2v 2 ( p T / 2) v B ( 2 p ) q T = 3v 2 ( p T / 3) T,µ,v Emitting medium is composed of unconfined, flowing quarks. 19

20 Sudden hadronization? Precocious quark number scaling: Accident or indicator of sudden hadronization? Bulk viscosity is large near Tc H. Meyer (quenched QCD) p eff = p ς v ζ/s Large ζ can induce thermodynamic instability (Fries, BM, Schäfer, arxiv: ) or hydrodynamic instabilities (Torrieri & Mishustin, arxiv: ), forcing fireball to hadronize suddenly. 20

21 Probing beyond the hadronic horizon with hadrons containing only s-, c-, and b-quarks 21

22 Ω/ϕ probes ϕ-mesons are produced via coalescence of apparently thermalized quarks in central Au+Au collisions. This observation implies hot and dense matter with partonic collectivity has been formed at RHIC. (STAR) 22

23 Heavy flavors: c, b Production process is unaffected by medium. Electrons from heavy flavor decays Transport & hadronization are affected by medium - evidence: RAA and v2 seen at RHIC. Bound states dissolve in the medium due to color screening and thermal ionization - and form by recombination near Tc? Comprehensive QCD-based theoretical framework missing: HQET + QCD-SR + HTL? 23

24 Thermal charmonium? Partonic flow? f (m T ) exp( m T / T s ) J/ψ Ω STAR Ξ ϕ 24

25 Statistical charmonium? Formation of J/ψ by statistical recombination of perturbatively produced, later thermalized charm quarks provides best representation of RHIC data: Andronic, Braun-Munzinger, Redlich & Stachel 25

26 The Future 26

27 Detector upgrades STAR forward meson spectrometer DAQ & TPC electronics Time of Flight barrel heavy flavor tracker barrel silicon tracker forward tracker PHENIX -completed ongoing in preparation hadron blind detector muon Trigger silicon vertex barrel (VTX) forward silicon forward EM calorimeter 27

28 Higher energies LHC CMS ALICE ATLAS 28

29 Theory Identify the model independent medium properties which can be determined with the help of quark flavor probes (susceptibilities, chemical relaxation times, diffusion coefficients, correlation/screening lengths, etc.) and develop robust observables which can be measured with precision. Develop a program involving collaboration among theorists and between theorists and experimentalists to extract physics from data. Adopt / join TEC-HQM model for hadronization and charm dynamics? 29

30 THE END 30