1 / 30

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.

jleal
Télécharger la présentation

Thermal Photons in Strong Interactions

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  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!

More Related