1 / 35

Electromagnetic Probes of Medium Effects in Heavy-Ion Collisions

Electromagnetic Probes of Medium Effects in Heavy-Ion Collisions. Ralf Rapp Cyclotron Institute + Physics Department Texas A&M University College Station, USA International on Workshop “Probing QCD with Heavy Ions” Hirschegg, 21.01.05. Outline. 1. Introduction

jovan
Download Presentation

Electromagnetic Probes of Medium Effects in Heavy-Ion Collisions

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. Electromagnetic Probes of Medium Effects in Heavy-Ion Collisions Ralf Rapp Cyclotron Institute + Physics Department Texas A&M University College Station, USA International on Workshop “Probing QCD with Heavy Ions” Hirschegg, 21.01.05

  2. Outline 1. Introduction 2. Chiral Symmetry in QCD 3. E.M. Emission and in-Medium Effects  E.M. Correlation Function + Chiral Symmetry  Vector Mesons in Medium  Photon and Dilepton Rates 4. Exp. Puzzles and Theoretical Attempts  Low-pt “Anomalies” at SPS (WA98, CERES/NA45) 5. Perspectives for RHIC 6. Conclusions

  3. low-massee in-medr,w,f →ee Chiral Symmetry restoration? int-massee continuum emission p a1→ ee , qq→ee QGP radiation? qq low-energy g hadron decays/scatt. a1→pg, pr→pg Medium effects? high-energy g continuum emission HG vs. QGP , O(as) QGP radiation? 1.) Four Pillars of Thermal E.M. Radiation Thermal rate: q0≈0.5GeV  Tmax≈0.17GeV , q0≈1.5GeV  Tmax=0.5GeV

  4. qR qL • Profound Consequences: • energy gap: • ↔ mass generation! • massless Goldstone bosonsp0,± • “chiral partners” split,DM≈0.5GeV: > > > > - - qR qL JP=0±1± 1/2± 2.) Chiral Symmetry in QCD:Vacuum SU(2)L × SU(2)R invariant (mu,d ≈ 0) - Spontaneous Breaking:strongqqattraction  Bose Condensate fillsQCD vacuum! [cf. Superconductor: ‹ee›≠0 Magnet ‹M›≠0 , … ]

  5. = O(1) = O(αs ) e+ e- γ 3.) 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:dependence onT, mB, mp , medium effects, … • system evolution:V(t), T(t), mB(t), transverse expansion, … • nonthermal sources: Drell-Yan, open-charm, hadron decays, … • consistency!

  6. rI =1 r+w+f _ qq 3.1 E.M. Correlator in Vacuum: s(e+e-→hadrons) h1 h2 e+ e- q q … _ s ≥ (1.5GeV)2 : pQCD continuum s < (1.5GeV)2 : V-meson spectral functs.

  7. At Tc: Chiral Restoration or:rlongchiral partner ofp≡ “Vector Manifestation” [Harada+ Yamawaki ’01] 3.2 Low-Mass Dileptons + Chiral Symmetry Im Πem(M)dominated by r-meson → chiral partner: a1(1260) Vacuum pQCD cont.

  8. Intermediate-Mass Dileptons 30% QGP [RR+ Shuryak ’99] Direct Photons [Turbide,RR+Gale’04] 3.3 Electromagnetic Probes at SPS: Anno ~2002 Low-Mass Dileptons Medium Effects! 10% QGP Baryon Density!

  9. 3.4. Vector Mesons in Medium r Sp > Sp > (b) Effective Field Theory HLS with rL≡p (“VM”); vacuum: loop exp.O(p/Lc , mr /Lc , g) In-Med.:T-dep. of bare mr(0), gr via matching to OPE, Lmatch<Lc + RG-running to on-shell  dropping r-mass [Harada, Yamawaki, Sasaki etal] [Chanfray etal, Herrmann etal, RR etal, Koch etal, Weise etal, Post etal, Eletsky etal, Oset etal, …] (a) Hadronic Many-Body Theory Dr(M,q:mB,T)=[M2-mr2-Srpp-SrB-SrM ]-1 Propagator: Constraints: -B,M→rN,rp -gN,gA,pN→rN - QCDSRs, lattice B*,a1,K1... N,p,K…

  10. rB/r0 0 0.1 0.7 2.6 Model Comparison [Eletsky etal ’01] [RR+Wambach ’99] r –Meson Spectral Functions Hot+Dense Matter Hot Meson Gas [RR+Gale ’99] [RR+Wambach ’99] • r-meson “melts” in hot and dense matter • baryon density rB more important than temperature

  11. - - [qq→ee] [qq+O(as)-HTL] Dilepton Emission Rates :dRee /dM2 ~ fB ImPem [Braaten,Pisarski +Yuan ’90] • HTL much • enhanced over • Born rate • “matching” of • HG and QGP • automatic! • Quark-Hadron • Duality ?!

  12. r Sp Hot and Dense Hadron Gas Emission Rates Low energy: vector dominance Sp q  Im Πem(q0=q) ~ Im Dvec(q0=q) g q p γ p,a1,w High energy: meson exchange r p In-med QGP ≈ total HG ! to be understood… [Kapusta,Lichard+Seibert ’91, … , Turbide,RR+Gale’04] 3.5 Thermal Photons Quark-Gluon Plasma “Naïve” LO: q + q (g) → g (q) +γ But:other contributions inO(αs) collinear enhanced Dg=(t-mD2)-1~1/αs Bremsstrahlung Pair-ann.+scatt. + ladder resummation (LPM) [Aurenche etal ’00, Arnold,Moore+Yaffe ’01]

  13. Expanding Fireball + pQCD [Turbide,RR+Gale’04] • pQCD+Cronin at qt >1.5GeV •  T0=205MeV suff., HG-dom. 4.1 Direct Photon Spectra: WA98 at SPS Hydrodynamics: QGP + HG [Huovinen,Ruuskanen+Räsänen ’02] • T0≈260MeV, QGP-dominated • still true if pp→gX included

  14. 4.1.2 WA98 “Low-qt Anomaly” Expanding Fireball Model Includepp→ppgS-wave [Turbide,RR+Gale’04] • current HG rate much below • 30% longer tFB 30% increase • slight improvement • in-medium “s” or D ?!

  15. Lower pt-cut • enhancement increases (well) • above theory • 40% longer lifetime insufficient 4.2 Low-Mass Dileptons Again: New CERES Data “Standard” pt-cut • theory: 30%-central scaled • by Nch ~ 375/250

  16. 4.2.2 Attempts at the Low-pt Anomaly II:Source Parameterization → LO-pQCD (QGP) emission rates (“quark-hadron duality”), space-time volume free parameter[Gallmeister+Kämpfer ’05] CERES/NA45 ’00 prelim • 2 sources required (shape!): T1≈170MeV + T2≈120MeV • shapes ok, but: very largeVFB∙ tFB(unrealistic …)

  17. 4.2.3 Attempts III:Disoriented Chiral Condensate → at Tc, condense in “misaligned” vacuum: ‹p› ≠ 0 , annihilate thermal p’s on DCC[Kluger,Koch,Randrup+Wang ’98] CERES/NA45 acceptance with pt>60MeV • DCC contribution ≈h Dalitz decay (much too small)

  18. 4.2.4 Attempts IV: QGP-like Emission → employ QGP-HTL rate in hadronic phase (just. at high mass) • enhancement above f almost ok ↔ NA50 • low mass?! Theoretically not justified …

  19. consistent with [Bratkovskaya etal ’98] 4.3 Low-Mass Dileptons at SIS / BEVALAC • Transport Calculation • [Shekhter,Fuchs etal ’03] • Extended VDM pp→ppw • “standard” calculation • factor 2-3 below data • improvement due to • decoherence in-medium • “optimal” values for • in-med. coll. broadening

  20. low mass: thermal dominant • int. mass:cc e+X , rescatt.? • e-X - 5.) Perspectives for RHIC I: Dileptons [Averbeck ‘01] [RR ’01] • Medium effects sensitive • to rB,tot=rB+rBbar !

  21. Dilepton Radiation ratio to pert. qq rate _ [Casalderrey+Shuryak’04] Mee/mq RHIC II: Bound States in the sQGP → based on finite-T lattice potentials approach to “zero-binding line”  ~ stable-massr-resonance [Shuryak,Zahed, Brown, …] • factor 2 enhancement • over pQCD rate!?

  22. 6.) Conclusions • Thermal E.M. Radiation in QCD: Pem(q0,q,mB,T) • - low mass: r,w,f,importance of baryon effects • - chiral restoration ↔r-a1degeneracy ( a1± → p± g ?!) • - thermal photons • extrapolations into phase transition region •  in-med HG and QGP shine equallybright • lattice calculations? deeper reason? • phenomenology for URHIC’s ok until 2002; • ’03/’04: low-pt anomalies in central Pb-Pb, new medium effects?? • much excitement ahead: NA60, HADES, PHENIX, ALICE,… • … and theory!

  23. Trento ECT* Workshop on Electromagnetic Probes in Heavy-Ion Collisions June 2-12, 2005 P. Braun-Munzinger, C. Gale + R. Rapp (coordinator)

  24. Additional Slides

  25. e+e- Emission Rates: dRee/dM ~ f B ImPem - - [qq→ee] [qq+O(as)] baryon effects important even at rB,net=0: sensitive to rB,tot=rB+rB , f more robust ↔ OZI in-med HG ≈ in-med QGP ! - Quark-Hadron Duality ?! (ii) Vector Mesons at RHIC

  26. 1- MEM 0- extracted [Laermann, Karsch ’04] 4.3 Lattice Studies of Medium Effects calculated on lattice p more stable than r below Tc?! (but: quenched)

  27. calculate integrate More direct! Proof of principle, not yet meaningful (need unquenched) 4.3.2 Comparison of Hadronic Models to LGT

  28. 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…

  29. 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]

  30. pS pS pS pS pS pP pP 5.1 Towards a Chiral + Resonance Scheme Options for resonance implementation: (i) generate dynamically from pion cloud [Lutz et al ‘03, …] (ii) genuine resonances on quark level → representations of chiral group [DeTar+Kunihiro ‘89, Jido etal ’00 ,…] e.g. p s N+ N(1535)- r a1D+ N(1520)- N(1900)+ D(1700)-(?) D(1920)+ rS (a1)S rS Importance of baryon spectroscopy to identify relevant decay modes!

  31. > D,N(1900)… Sp a1 Sp + + . . . > N(1520)… Sr > > Exp: - HADES(pA): a1→(p+p-)p - URHICs (AA): a1→pg 5.2 Current Status of a1(1260)

  32. 7.2 Perspectives on Photon Data at RHIC Predictions for Central Au-Au PHENIXData • large “pre-equilibrium” yield • from parton cascade (no LPM) • thermal yields ~ consistent • QGP undersat. small effect • consistent with pQCD only • disfavors parton cascade • not sensitive to thermal yet

  33. 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]

  34. Rho Spectral Function at Future GSI • high-density effects most prominent at low mass

  35. a=1±(qq) (qqq) Chiral breaking: Q2 < (1.5-2 GeV)2 , J± < 5/2 (?!) 2.1 Light Hadrons: Vacuum Correlation Function: Timelike (q2>0) : ImPa(q0,q) → physical excitations

More Related