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Vector Mesons in Medium and Dileptons in Heavy-Ion Collisions

Heavy-Quark Diffusion in the Primordial Quark-Gluon Liquid. Vector Mesons in Medium and Dileptons in Heavy-Ion Collisions. Ralf Rapp Cyclotron Institute + Physics Department Texas A&M University College Station, USA Strong Interaction Seminar TU M ünchen , 26.10.09.

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Vector Mesons in Medium and Dileptons in Heavy-Ion Collisions

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  1. Heavy-Quark Diffusion in the Primordial Quark-Gluon Liquid Vector Mesons in Medium and Dileptons in Heavy-Ion Collisions Ralf Rapp Cyclotron Institute + Physics Department Texas A&M University College Station, USA Strong Interaction Seminar TU München, 26.10.09

  2. 1.) Intro-I:Probing Strongly Interacting Matter • Electromagnetic Probes: • penetrating:lEM >> Rnuc • Equilibrium: • EM spectral function • Im PEM(q0,q;mB,T) • Information via EM Spectral Function: • degrees of freedom (parton vs. hadron) • transport properties (EM conductivity, susceptibility) • relation to order parameters (chiral symmetry) • measure of temperature

  3. 1.2) Intro-IIa: Low-Mass Dileptons at CERN-SPS CERES/NA45 [2000] NA60 [2005] mee [GeV] • strong excess around M ≈ 0.5GeV (and M > 1GeV ) • little excess in r, w, f region

  4. 1.2) Intro-IIb:Low-Mass Dileptons SIS + RHIC HADES [2008] PHENIX [2008] mee [GeV] • awaiting larger system sizes … • very large low-mass excess • awaiting HBD results (run-10) …

  5. Outline 1.) Introduction 2.) Chiral Symmetry + Vector Mesons  EM Emission and Vector Mesons  Chiral Symmetry Breaking  r and a1 Meson in Medium 3.) Dilepton Spectra in A-A and g-A  Thermal Emission and NA60 (SPS)  Photoproduction and CLAS (JLab) 4.) Conclusions

  6. e+ e- γ 2.1 Thermal Electromagnetic Emission EM Current-Current Correlation Function: Thermal Dilepton and Photon Production Rates: Im Πem(M,q) Im Πem(q0=q) r-meson dominated Low Mass: ImPem~ [ImDr + ImDw /10 + ImDf /5]

  7. qR qL • Profound Consequences: • effective quark-mass: • ↔ mass generation • massless Goldstone bosonsp0,±, • pion pole-strength fp = 93MeV • “chiral partners” split,DM ≈ 0.5GeV: > > > > - - qL qR JP=0±1± 1/2± 2.2 Chiral Symmetry + QCD Vacuum : isospin + “chiral” (left/right-handed) invariant But: “Higgs” Mechanism in Strong Interactions: qq attraction “Bose” condensate fills QCD vacuum Spontaneous Chiral Symmetry Breaking -

  8. 2.3 Hadron Spectra + Chiral Symm. Breaking Axial-/Vector Correlators Constituent Quark Mass “Data”: lattice [Bowman et al ‘02] Theory: Instanton Model [Diakonov+Petrov; Shuryak ‘85] pQCD cont. • Weinberg Sum Rule(s) • chiral breaking:|q2| ≤ 1 GeV2 • Gellmann Oakes Renner: • mp2 fp2 = mq‹0|qq|0› -

  9. 2.4 Sum Rules and Order Parameters • Weinberg-SRs: momentsVector-Axialvector [Weinberg ’67, Das et al ’67, Kapusta+Shuryak ‘93] • QCD-SRs [Hatsuda+Lee ’91, Asakawa+Ko ’92, Klingl et al ’97, Leupold et al ’98, Kämpfer et al ‘03, Ruppert et al ’05, Kwon et al ‘08]  Promising synergy of lQCD and effective models

  10. 2.5 r-Meson in Medium: Hadronic Interactions > rB /r0 0 0.1 0.7 2.6 > rMeson “Melting” Switch off Baryons [RR,Wambach et al ’99] [Chanfray et al, Herrmann et al, RR et al, Koch et al, Klingl et al, Mosel et al, Eletsky et al, Oset et al, Sasaki et al …] Dr (M,q;mB ,T) = [M 2 - mr2 -Srpp -SrB -SrM ] -1 r-Propagator: B*,a1,K1... r Sp r SrB,rM= Selfenergies: Srpp= N,p,K… Sp Constraints:decays:B,M→ rN, rp, ... ; scattering:pN→rN, gA, …

  11. p Sp Sp Sp r Sr Sr Sr 2.6 Axialvector in Medium: Dynamical a1(1260) p a1 resonance + + . . . = Vacuum: r In Medium: + + . . . • in-medium p + r propagators • substantial broadening of • p-r scattering amplitude • consequences for chiral • restoration to be elaborated [Cabrera,Jido,Roca+RR ’09 in preparation]

  12. e+ e- q q _ Thermal Sources:Relevance: - Quark-Gluon Plasma: high mass + temp. qq → e+e-, …M >1.5GeV, T >Tc - Hot + Dense Hadron Gas: M ≤ 1 GeV p+p- → e+e-, … T ≤ Tc - e+ e- p- p+ r(770) 3.) Dilepton Spectra in A-A and g-A Thermal Dilepton Emission Rate: e+ e- g* Im Πem(M,q;mB,T) Im Πem ~ Im Dr

  13. - [qq→ee] [HTL] 3.1 Dilepton Rates: Hadronic vs. QGPdRee /dM2 ~ ∫d3q f B(q0;T) ImPem • Hard-Thermal-Loop [Braaten et al ’90] • enhanced over Born rate • Hadronic and QGP rates • “degenerate” around~Tc • Quark-Hadron Duality at all M?! • ( degenerate axialvector SF!)

  14. 3.2 Dilepton “Excess” Spectra at SPS Thermal Emission Spectrum: • “average” Gr (T~150MeV) ~ 350-400 MeV • Gr (T~Tc) ≈ 600 MeV → mr • fireball lifetime: tFB ~ (6.5±1) fm/c [van Hees+RR ‘06, Dusling et al ’06, Ruppert et al ’07, Bratkovskaya et al ‘08]

  15. 3.2.2 NA60 Data vs. In-Medium Dimuon Rates Mmm [GeV] [van Hees +RR ’07] [RR,Wambach et al ’99] • acceptance-corrected data directly reflect thermal rates!

  16. Intermediate Mass Region 3.2.3 NA60 Dimuons: Sensitivity to QGP and Tc • vary critical and chemical-freezeout temperature (Tfo ~ 130 MeV fix) “EoS-B” “EoS-C” • overall shape of spectra robust: “duality” of dilepton rate around “Tc”! • yields slightly larger for large Tc (hadronic volume!), |Dt| < 1fm/c • intermediate mass (M>1GeV): QGP vs. hadronic depends on Tc

  17. 3.3 Low-Mass Dileptons at RHIC: PHENIX • Successful approach at SPS fails at RHIC

  18. 3.4 r Meson in Cold Nuclear Matter Theoretical Approach: [Riek et al ’08] in-medium r spectral function elementary production amplitude + Fe-Ti rN ≈ 0.5 r0 r g N Mee[GeV] M[GeV] Nuclear Photo-Production: r e+ e- g + A → e+e- X Eg=1.5-3GeV g [CLAS/JLab ‘08]

  19. 4.) Conclusions • Electromagnetic Probes • - study matter properties in nuclear reactions • - low mass: in-medium vector mesons • Chiral Symmetry Breaking (Restoration) • - chiral partners: r - a1 (degeneracy at Tc) • Thermal Dilepton Rates • - melting r toward Tc (quark-hadron duality?) • Dilepton Spectra • - quantitative agreement at SPS • - ok at TJNAF (g-A) • - failure at RHIC thus far

  20. 4.5 EM Probes in Central Pb-Au/Pb at SPS Di-Electrons [CERES/NA45] Photons [WA98] • updated fireball (aT=0.045→0.085/fm) • very low-mass di-electrons ↔ (low-energy) photons [van Hees+RR ‘07] [Srivastava et al ’05, Liu+RR ‘06]

  21. > > > > Exp: - HADES(pA): a1→(p+p-)p - URHICs (A-A) : a1→pg 4.8 Axialvector in Medium: Explicit a1(1260) D,N(1900)… Sp a1 Sp + + . . . N-1 Sr N(1520)…

  22. 2.5Cold Nuclear Matter: r Photo-Production g + A → e+e- X [CLAS/JLab +GiBUU ’08] Eg=1.5-3GeV Fe-Ti rN ≈ 0.5 r0 [Riek et al ’08]

  23. 2.3.2 Acceptance-Corrected NA60 Spectra Mmm [GeV] Mmm [GeV] • more involved at pT>1.5GeV: Drell-Yan, primordial/freezeout r , …

  24. X.) Example for Comprehensive Analysis: NA60 Dileptons Charmonium Flow Charmonium Production  thermal medium radiating from around Tc with meltedr , well-boundJ/y with large collectivity

  25. 2.4 r Spectral Function at Lower Collision Energies • largest sensitivity for M ≤ 0.4 GeV - soft modes! • Critical point:s - wL mixing (q≠0) withms→ 0, • but: w → e+e-signal (too) weak

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