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Thermal Photons in Strong Interactions

Thermal Photons in Strong Interactions. Ralf Rapp Cyclotron Inst. + Physics Dept. Texas A&M University College Station, USA College Station, 24.09.04. c PT many-body degrees of freedom? QGP (2 ↔ 2) (3-body,...) (resonances?) consistent extrapolate pQCD.

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Thermal Photons in Strong Interactions

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  1. Thermal Photons in Strong Interactions Ralf Rapp Cyclotron Inst. + Physics Dept. Texas A&M University College Station, USA College Station, 24.09.04

  2. cPTmany-bodydegrees of freedom?QGP (2 ↔ 2)(3-body,...) (resonances?) consistentextrapolatepQCD 0 0.05 0.3 0.75 e[GeVfm-3] 120 150-160 175 T [MeV] ½r0 2r0 5r0rhadron Introduction I:E.M. Probes in Strong Interactions • g-ray spectroscopy of atomic nuclei: collective phenomena • DIS off the nucleon: - parton model, PDF’s (high Q2) • - nonpert. structure of nucleon [JLAB] • thermal emission: - compact stars (?!) • - heavy-ion collisions • What is the electromagnetic spectrum of matter?

  3. Outline 1. Introduction 2. Thermal Photon Emission Rates 2.1 Generalities 2.2 Quark-Gluon Plasma:Complete LO 2.3 Hadronic Matter:-Meson Gas - Baryonic Contributions - Medium Effects 3. Relativistic Heavy-Ion Collisions 3.1 Nonthermal Sources 3.2 Thermal Evolution 3.3 Comparison to SPS and RHIC Data 4. High-Density QCD: Colorsuperconductor 5. Conclusions

  4. = O(1) = O(αs ) e+ e- γ Introduction II:Electromagnetic Emission Rates E.M. Correlation Function: Im Πem(M,q) Im Πem(q0=q) also: e.m susceptibility (charge fluct):χ = Πem(q0=0,q→0) • In URHICs: • source strength:depend. onT, mB, mp ; medium effects, … • system evolution:V(t), T(t), mB(t); transverse expansion, … • nonthermal sources:e+e-: Drell-Yan, open-charm; g: initial/ • consistency! pre-equil.

  5. T Im Πem(q0=q) p γ r cut 2 p γ kinetic theory: r p |M|2 2. Thermal Photon Radiation 2.1 Generalities Emission Rate per 4-volume and 3-momentum transverse photon selfenergy many-body language: in-medium effects, resummations, …

  6. But: other contributions toO(αs) collinear enhanced Dg=(t-mD2)-1 ~ 1/αs Bremsstrahlung Pair-ann.+scatt. + ladder resummation (LPM) [Aurenche etal ’00, Arnold,Moore+Yaffe ’01] 2.2 Quark-Gluon Plasma “Naïve” Leading Order Processes: q + q (g) → g (q) + γ q q g [Kapusta etal ’91, Baier etal ’92]

  7. HLS MYM Kap.’91 (no a1) p p γ γ • Photon-producing reactions: p,a1 r p r p p,a1 mostly at dominant (q0>0.5GeV) gauge invariance! q0<0.5GeV a1-strength problematic 2.3.1 Hot Hadronic Matter: p-r-a1 Gas Chiral Lagrangian + Axial/Vector-mesons, e.g. HLS or MYM: • (g0,m0,s,x)fit tomr,a1 ,Gr,a1 • D/SandG(a1→pγ)not optimal [Song ’93, Halasz etal ’98,…]

  8. Factor 3-4 suppression at intermediate and high photon energies 2.3.1.b Hadronic Formfactors • quantitative analysis: account for finite hadron size • improves a1phenomenology • t-channel exchange: gauge invariance nontrivial [Kapusta etal ’91] • simplified approach: [Turbide,Gale+RR ’04] with

  9. p γ p γ p K K* K K* (ii) wt-Channel p γ Gwrplarge! potentially important … w [Turbide,Gale +RR ’04] r p 2.3.2 Further Meson Gas Sources (i) Strangeness Contributions: SU(3)F MYM ~25%of pp→ργ ~40%of pr→pγ! (iii) Higher Resonances Ax-Vec:a1,h1→pg,Vec:w,w’,w’’→pgother:p(1300)→pg f1→rg,K1→KgK*→Kg a2(1320)→pg

  10. r Sp > Sp > g N → p N,D gN gA g N → B* p-ex [Urban,Buballa,RR+Wambach ’98] 2.3.3 Baryonic Contributions • use in-medium r –spectral funct: • constrained by nucl. g-absorption: B*,a1,K1... N,p,K…

  11. 2.3.3(b) Photon Rates from r Spectral Function:Baryons + Meson-Resonances • baryonic contributions • dominant forq0<1GeV • (CERES enhancement!) • also true at RHIC+LHC: • atT=180MeV, mB=0 mB=220MeV

  12. 2.3.4 HG Emission Rates: Summary • wt-channel (very) important • at high energy • formfactor suppression (2-4) • strangeness significant • baryons at low energy mB=220MeV [Turbide,RR+Gale ’04]

  13. 2.3.5 In-Medium Effects • many-body approach: encoded in vector-spectral function, • relevant below M , q0 ~ 1-1.5 GeV • “dropping masses”: • large enhancement due • to increased phase space • [Song+Fai ’98, Alam etal ’03] • unless: • vector coupling decreases • towards Tc (HLS, a→1) • [Harada+Yamawaki ’01, • Halasz etal ’98]

  14. Similar findings for • thermal dilepton rates • not yet understood … 2.3.6 Hadron Gas vs. QGP Emission • complete LO QGP rate • ~2-3 above tree-level rate • in-med HG + Meson-Ex • (bottom-up) • ≈ • complete LO QGP • (top-down) • “quark-hadron duality” ?!

  15. e+ e- J/y r Au + Au QGP ?! Hadron Gas “Freeze-Out” • Signatures of the QGP? • Suppression of J/y Mesons • Decays of r-Mesons • Photons … Au + Au → X 3. Relativistic Heavy-Ion Collisions

  16. Nuclear Effects: pA → gX • “Cronin”: gaussian kt-smear. • cf. pA → πX • AA: <Dkt2>AA≈ 2<Dkt2>pA 3.1 Nonthermal Sources Initial hard production: pp → γX scaling with xT=2pT /√s , + power-law fit[Srivastava ’01]

  17. HG: chemistry and trans. flow HG: chemistry [LHC] T [GeV] • R~exp(3mp) for pr→pg , … • yield up at low qt , down above • large blue shift from coll. flow • conserved BB use entropy • build-up of mp>0 (Np=const) • accelerated cooling 3.2 Thermal Evolution:QGP→ Mix→ HG QGP: initial conditions [SPS] • t0=1fm/c → t0=0.5fm/c: ~2-3 • s=CdQGT3; dQG=40 → 32: ~2 • pre-equilibrium?!

  18. Expanding Fireball + Initial [Turbide,RR+Gale’04] • initial+Cronin at qt >1.5GeV •  T0=205MeV suff., HG dom. 3.3 Comparison to Data I: WA98 at SPS Hydrodynamics: QGP + HG [Huovinen,Ruuskanen+Räsänen ’02] • T0≈260MeV, QGP-dominated • still true if pp→gX included

  19. Include pp→ppgS-wave • slight improvement • in-medium “s” or D ?! 3.3 Comp. to Data II: WA98 “Low-qt Anomaly” Expanding Fireball Model [Turbide,RR+Gale’04] • current HG rate much below • 30% longer tFB 30% increase

  20. 3.3 Perspectives on Data III: RHIC Predictions for Central Au-Au PHENIX Data • large “pre-equilibrium” yield • from parton cascade (no LPM) • thermal yields ~ consistent • QGP undersat. small effect • consistent with initial only • disfavors parton cascade • not sensitive to thermal yet

  21. Photon Emissivities Effective theory description of “hadronic” processes: γ γ  exceeds e+e-→γγforT≥5MeV [Vogt,Ouyed+RR] 4. Photon Emission from Colorsuperconductor Cold Quark Matter → (qq) Cooper pairs, Dqq≈100MeV mq» ms2 : u-d-s symmetrically paired (Color-Flavor-Locking)  ciral symmetry broken, Goldstone bosons, mp2 ~ mq2 ≈ (10MeV)2

  22. 5. Conclusions • significant progress in E.-M. radiation from QCD matter: • - QGP: soft collinear enhancement → complete leading order • - HG: more complete (strangeness, baryons, w t-chan, FF’s) • extrapolations into phase transition region •  HG and QGP shine equally bright • deeper reason? lattice calculations? • phenomenology for URHIC’s compares favorably • with existing data • consistency with dileptons • much excitement ahead: PHENIX, NA60, HADES, ALICE,… • and theory!

  23. Additional Slides

  24. Photon Properties in Colorsuperconductors

  25. 2.2.2 1± Mesons: B*,a1,K1... r Sp + > N,p,K… Sp > Significance of high rB at low M Elab=20-40AGeV optimal?! (i) r(770) Constraints: - branching ratiosB,M→rN,rp -gN,gAabsorpt.,pN→rN - QCD sum rules

  26. NN-1DN-1 Sp D + + + + ... > > > > > pD→N(1440), N(1520), D(1600) > in-medium vertex corrections incl. g’ p-cloud, (“induced interaction”) (1+ f p - f N) thermal p-gas > > 2.2.4 In-Medium Baryons: D(1232) long history in nuclear physics ! (pA , gA ) e.g. nuclear photoabsorption:MD, GDup by 20MeV  little attention at finite temperature  D-Propagator at finite rB and T[van Hees + RR ’04]

  27. (i) Check: D in Vacuum and in Nuclei → ok !

  28. (ii) D(1232) in URHICs  broadening: Bose factor, pD→B  repulsion: pDN-1, pNN-1 not yet included: (pN→D)

  29. calculate integrate More direct! Proof of principle, not yet meaningful (need unquenched) Comparison of Hadronic Models to LGT

  30. Im Πem(M,q) Im Πem(q0=q) 2.2.6 Observables in URHICs e+ e- γ (i) Lepton Pairs(ii) Photons [Turbide,Gale+RR ’03] • consistent with dileptons • pp Brems with soft s at low q? baryon density effects!

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