1 / 47

Thermal Electromagnetic Radiation in Heavy-Ion Collisions

Thermal Electromagnetic Radiation in Heavy-Ion Collisions. Ralf Rapp Cyclotron Institute + Dept of Phys & Astro Texas A&M University College Station, USA 34 th International School of Nuclear Physics “Probing the Extremes of Matter with Heavy Ions”

kbliss
Download Presentation

Thermal Electromagnetic Radiation 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. Thermal Electromagnetic Radiation in Heavy-Ion Collisions Ralf Rapp Cyclotron Institute + Dept of Phys & Astro Texas A&M University College Station, USA 34th International School of Nuclear Physics “Probing the Extremes of Matter with Heavy Ions” Erice (Sicily, Italy), 20.09.12

  2. 1.) Intro: EM Spectral Function + Fate of Resonances Im Pem(M) in Vacuum Im Πem(M,q;mB,T) • Electromagn. spectral function • -√s < 2 GeV: non-perturbative • -√s > 2 GeV: perturbative (“dual”) • Vector resonances “prototypes” • - representative for bulk hadrons: • neither Goldstone nor heavy flavor • Modifications of resonances • ↔ phase structure: • - hadron gas → Quark-Gluon Plasma • - realization of transition? e+e-→ hadrons √s = M

  3. 1.2 Phase Transition(s) in Lattice QCD Tpcc~155MeV [Fodor et al ’10] • cross-over(s) ↔ smooth EM emission rates across Tpc • chiral restoration in “hadronic phase”? (low-mass dileptons!) • hadron resonance gas - - ≈ qq / qq0

  4. Outline 2.) Spectral Function + Emission Temperature  In-Medium r + Dilepton Rates  Dilepton Mass Spectra + Slopes  Excitation Function + Elliptic Flow 3.) Chiral Symmetry Restoration  Chiral Condensate  Weinberg + QCD Sum Rules  Euclidean Correlators 4.) Conclusions

  5. 2.1 Vector Mesons in Hadronic Matter > rB /r0 0 0.1 0.7 2.6 > [Chanfray et al, Herrmann et al, Asakawa et al, RR et al, Koch et al, Klingl et al, Post et al, Eletsky et al, Harada 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, … SPS RHIC / LHC

  6. 2.2 Dilepton Rates: Hadronic - Lattice - Perturbative dRee /dM2 ~ ∫d3q f B(q0;T) Im Pem dRee/d4q 1.4Tc (quenched) q=0 • continuous rate through Tpc • 3-fold “degeneracy” toward~Tpc - [qq→ee] [HTL] [Ding et al ’10] [RR,Wambach et al ’99]

  7. 2.3 Dilepton Rates vs. Exp.: NA60 “Spectrometer” • Evolve rates over fireball expansion: Acc.-correctedm+m- Excess Spectra In-In(17.3GeV) [NA60 ‘09] [van Hees+RR ’08] Mmm [GeV] • invariant-mass spectrum directly reflects thermal emission rate!

  8. 2.4 Dilepton Thermometer: Slope Parameters Invariant Rate vs. M-Spectra Transverse-Momentum Spectra cont. Tc=160MeV Tc=190MeV r • Low mass: radiation from around T ~ Tpcc ~ 150MeV • Intermediate mass: T ~ 170 MeV and above • Consistent with pT slopes incl. flow: Teff ~ T + M (bflow)2

  9. 2.5 Low-Mass e+e- Excitation Function: SPS - RHIC Pb-Au(8.8GeV) Au-Au min. bias QM12 Pb-Au(17.3GeV) • no apparent change of the emission source • consistent with “universal” medium effect around Tpc • partition hadronic/QGP depends on EoS, total yield ~ invariant

  10. 2.6 Direct Photons at RHIC Spectra Elliptic Flow ← excess radiation • Teffexcess = (220±25) MeV • QGP radiation? • radial flow? • v2g,dir comparable to pions! • under-predicted by early QGP • emission [Holopainen et al ’11,…]

  11. 2.6.2 Thermal Photon Spectra + v2 thermal + prim. g [van Hees,Gale+RR ’11] • hadronic emission close to Tpc essential (continuous rate!) • flow blue-shift: Teff ~ T √(1+b)/(1-b) • e.g. b=0.3: T ~ 220/1.35~ 160 MeV • small slope + large v2 suggest main emission around Tpc • confirmed with hydro evolution [He at al in prep.]

  12. Outline 2.) Spectral Function + Emission Temperature  In-Medium r + Dilepton Rates  Dilepton Mass Spectra + Slopes  Excitation Function + Elliptic Flow 3.) Chiral Symmetry Restoration  Chiral Condensate  Weinberg + QCD Sum Rules  Euclidean Correlators 4.) Conclusions

  13. 3.1 Chiral Condensate + r-Meson Broadening > Sp effective hadronic theory > - Sp • h = mq h|qq|h > 0 contains quark core + pion cloud • = Shcore + Shcloud ~ + • matches spectral medium effects: resonances + pion cloud • resonances + chiral mixing drive r-SF toward chiral restoration - - qq / qq0

  14. 3.2 Spectral Functions + Weinberg Sum Rules • Quantify chiral symmetry breaking via observable spectral functions • Vector (r) - Axialvector (a1) spectral splitting [Weinberg ’67, Das et al ’67; Kapusta+Shuryak ‘93] t→(2n+1)p t→(2n)p [ALEPH ’98,OPAL ‘99] rA/s rV/s pQCD pQCD • Updated “fit”: [Hohler+RR ‘12] • r+a1 resonance, excited states (r’+a1’), universal continuum (pQCD!)

  15. 3.2.2 Evaluation of Chiral Sum Rules in Vacuum • pion decay • constants • chiral quark • condensates • vector-axialvector splitting quantitative observable of • spontaneous chiral symmetry breaking • promising starting point to analyze chiral restoration

  16. 3.3 QCD Sum Rules at Finite Temperature [Hatsuda+Lee’91, Asakawa+Ko ’93, Klingl et al ’97, Leupold et al ’98, Kämpfer et al ‘03, Ruppert et al ’05] rV/s T [GeV] Percentage Deviation • r and r’ melting • compatible with • chiral restoration [Hohler +RR ‘12]

  17. 3.4 Vector Correlator in Thermal Lattice QCD • Euclidean Correlation fct. Lattice (quenched) [Ding et al ‘10] Hadronic Many-Body [RR ‘02] • “Parton-Hadron Duality” of lattice and in-medium hadronic?

  18. 4.) Conclusions • Low-mass dilepton spectra in URHIC point at universal source • r-meson gradually melts into QGP continuum radiation • prevalent emission temperature around Tpc~150MeV (slopes, v2) • mechanisms underlying r-melting (p cloud + resonances) find • counterparts in hadronic S-terms, which restore chiral symmetry • quantitative studies relating r-SF to chiral order parameters with • QCD and Weinberg-type sum rules • Future precise characterization of EM emission source at • RHIC/LHC + CBM/NICA/SIS holds rich info on QCD phase • diagram (spectral shape, source collectivity + lifetime)

  19. 2.3 QCD Sum Rules: r and a1 in Vacuum • dispersion relation: [Shifman,Vainshtein+Zakharov ’79] • lhs:hadronic spectral fct. • rhs:operator product expansion • 4-quark + gluon condensate dominant vector axialvector

  20. 4.5 QGP Barometer: Blue Shift vs. Temperature SPS RHIC • QGP-flow driven increase of Teff ~ T + M (bflow)2 at RHIC • high pt: high T wins over high-flow r’s → minimum (opposite to SPS!) • saturates at “true” early temperature T0 (no flow)

  21. 4.3.2 Revisit Ingredients Emission Rates Fireball Evolution • multi-strange hadrons at “Tc” • v2bulkfully built up at hadronization • chemical potentials for p, K, … • Hadron - QGP continuity! • conservative estimates… [Turbide et al ’04] [van Hees et al ’11]

  22. 4.1.3 Mass Spectra as Thermometer Emp. scatt. ampl. + T-r approximation Hadronic many-body Chiral virial expansion Thermometer [NA60, CERN Courier Nov. 2009] • Overall slope T~150-200MeV (true T, no blue shift!)

  23. 4.1.2 Sensitivity to Spectral Function In-Medium r-Meson Width • avg. Gr(T~150MeV)~370MeVGr (T~Tc) ≈ 600 MeV → mr • driven by (anti-) baryons Mmm [GeV]

  24. 5.1 Thermal Dileptons at LHC • charm comparable, accurate (in-medium) measurement critical • low-mass spectral shape in chiral restoration window

  25. 5.2 Chiral Restoration Window at LHC • low-mass spectral shape in chiral restoration window: • ~60% of thermal low-mass yield in “chiral transition region” • (T=125-180MeV) • enrich with (low-) pt cuts

  26. 4.3 Dimuon pt-Spectra and Slopes: Barometer Effective Slopes Teff • theo. slopes originally too soft • increase fireball acceleration, • e.g. a┴ = 0.085/fm → 0.1/fm • insensitive to Tc=160-190MeV

  27. 3.4.2 Back to Spectral Function • suggests approach to chiral restoration + deconfinement

  28. 4.2 Low-Mass e+e- at RHIC: PHENIX vs. STAR • “large” enhancement not accounted • for by theory • cannot be filled by QGP radiation… • (very) low-mass region • overpredicted… (SPS?!)

  29. 4.4 Elliptic Flow of Dileptons at RHIC • maximum structure due to • late r decays [He et al ‘12] [Chatterjee et al ‘07, Zhuang et al ‘09]

  30. 4.2 Low-Mass Dileptons: Chronometer In-In Nch>30 • first “explicit” measurement of interacting-fireball lifetime: • tFB≈ (7±1) fm/c

  31. p Sp Sp Sp r Sr Sr Sr 3.2 Axialvector in Nucl. Matter: Dynamical a1(1260) p a1 resonance + + . . . = Vacuum: r In Medium: + + . . . [Cabrera,Jido, Roca+RR ’09] • in-medium p + r propagators • broadening of p-r scatt. Amplitude • pion decay constant in medium:

  32. 3.6 Strategies to Test For Chiral Restoration eff. theory for VC + AV spectral functs. Lat-QCD Euclidean correlators vac. data + elem. reacts. (gA→eeX, …) constrain Lagrangian (low T, rN) constrainVC + AV : QCD SR Lat-QCD condensates + c ord. par. EM data in heavy-ion coll. test VC - AV: chiral SRs global analysis of M, pt, v2 Realistic bulk evol. (hydro,…) Agreement with data? Chiral restoration?

  33. 4.1 Quantitative Bulk-Medium Evolution • initial conditions (compact, initial flow?) • EoS: lattice (QGP, Tc~170MeV) + chemically frozen hadronic phase • spectra + elliptic flow: multistrange at Tch ~ 160MeV • p, K, p, L, … at Tfo ~ 110MeV • v2 saturates at Tch, good light-/strange-hadron phenomenology [He et al ’11]

  34. qR qL > > > > - - qL qR 2.1 Chiral Symmetry + QCD Vacuum : flavor + “chiral” (left/right) invariant • “Higgs” Mechanism in Strong Interactions: • qqattraction  condensate fills QCD vacuum! • Spontaneous Chiral Symmetry Breaking - • Profound Consequences: • effective quark mass: • ↔ mass generation! • near-massless Goldstone bosons p0,± • “chiral partners” split: DM ≈ 0.5GeV JP=0±1± 1/2±

  35. 2.3.2 NA60 Mass Spectra: pt Dependence Mmm [GeV] • more involved at pT>1.5GeV: Drell-Yan, primordial/freezeout r , …

  36. 4.4.3 Origin of the Low-Mass Excess in PHENIX? • QGP radiation insufficient: • space-time , lattice QGP rate + • resum. pert. rates too small • must be of long-lived hadronic origin • Disoriented Chiral Condensate (DCC)? • Lumps of self-bound pion liquid? • Challenge: consistency with hadronic data, NA60 spectra! [Bjorken et al ’93, Rajagopal+Wilczek ’93] - “baked Alaska” ↔ small T - rapid quench+large domains ↔ central A-A - ptherm + pDCC → e+ e- ↔ M~0.3GeV, small pt [Z.Huang+X.N.Wang ’96 Kluger,Koch,Randrup ‘98]

  37. 2.2 EM Probes at SPS • all calculated with the same e.m. spectral function! • thermal source: Ti≈210MeV, HG-dominated, r-meson melting!

  38. 5.2 Intermediate-Mass Dileptons: Thermometer • use invariant continuum radiation (M>1GeV): no blue shift, Tslope = T ! Thermometer • independent of partition HG vs QGP (dilepton rate continuous/dual) • initial temperature Ti ~ 190-220 MeV at CERN-SPS

  39. 4.7.2 Light Vector Mesons at RHIC + LHC • baryon effects important even at rB,tot= 0 : • sensitive to rBtot= rB + rB (r-N and r-N interactions identical) • w also melts, f more robust ↔ OZI - -

  40. = = 5.3 Intermediate Mass Emission: “Chiral Mixing” [Dey, Eletsky +Ioffe ’90] • low-energy pion interactions fixed by chiral symmetry 0 0 0 0 • mixing parameter • degeneracy with perturbative • spectral fct. down to M~1GeV • physical processes at M≥ 1GeV: • pa1→ e+e- etc. (“4p annihilation”)

  41. 3.2 Dimuon pt-Spectra and Slopes: Barometer pions: Tch=160MeV a┴ =0.1/fm pions: Tch=175MeV a┴ =0.085/fm • modify fireball evolution: • e.g. a┴ = 0.085/fm → 0.1/fm • both large and small Tccompatible • with excess dilepton slopes

  42. 2.3.3 Spectrometer III: Before Acceptance Correction emp. ampl. + “hard” fireball hadr. many-body + fireball schem. broad./drop. + HSD transport chiral virial + hydro • Discrimination power much reduced • can compensate spectral “deficit” by larger flow: lift pairs into acceptance

  43. 4.2 Improved Low-Mass QGP Emission • LO pQCD spectral function: rV(q0,q) = 6∕9 3M2/2p [1+QHTL(q0)] • 3-momentum augmented lattice-QCD rate (finite g rate)

  44. 4.1 Nuclear Photoproduction: rMeson in Cold Matter g + A → e+e- X • extracted • “in-med” r-width • Gr≈ 220 MeV e+ e- Eg≈1.5-3 GeV g r [CLAS+GiBUU ‘08] • Microscopic Approach: + in-med. r spectral fct. product. amplitude full calculation fix density 0.4r0 Fe-Ti r g N [Riek et al ’08, ‘10] M[GeV] • r-broadening reduced at high 3-momentum; need low momentum cut!

  45. 2.3.6 Hydrodynamics vs. Fireball Expansion • very good agreement • between original • hydro [Dusling/Zahed] • and fireball [Hees/Rapp]

  46. 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]

  47. 3.5 Summary: Criteria for Chiral Restoration • Vector (r) – Axialvector (a1) degenerate [Weinberg ’67, Das et al ’67] pQCD • QCD sum rules: • medium modifications ↔ vanishing of condensates • Agreement with thermal lattice-QCD • Approach to perturbative rate (QGP)

More Related