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Update on Search for Chiral Symmetry Restoration in Heavy-Ion Collisions

Update on Search for Chiral Symmetry Restoration in Heavy-Ion Collisions. Ralf Rapp Cyclotron Institute + Dept of Phys & Astro Texas A&M University College Station, USA 11 th Int. Conference on Nucleus-Nucleus Collisions San Antonio (Texas), 29.05.12.

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Update on Search for Chiral Symmetry Restoration in Heavy-Ion Collisions

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  1. Update on Search for Chiral Symmetry Restoration in Heavy-Ion Collisions Ralf Rapp Cyclotron Institute + Dept of Phys & Astro Texas A&M University College Station, USA 11th Int. Conference on Nucleus-Nucleus Collisions San Antonio (Texas), 29.05.12

  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 - - ≈ qq / qq “Tcchiral”~155MeV “Tcconf” ~170MeV [Fodor et al ’10] • cross-over(s) ↔ smooth e+e- rate • chiral restoration in “hadronic phase”?! • (low-mass dileptons!) • hadron resonance gas

  4. Outline 2.) Chiral Symmetry Breaking in Vacuum  “Higgs Mechanism”, Condensates + Mass Gap in QCD  Hadron Spectrum, Chiral Partners + Sum Rules 3.) EM Spectral Function in Medium  Hadronic Theory  QGP + Lattice QCD 4.) EM Probes in Heavy-Ion Collisions  Spectro-, Thermo-, Chrono- + Baro-meter  Thermal Photons  Pt Spectra + Collectivity 5.) Conclusions

  5. 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±

  6. 2.2 Chiral (Weinberg) Sum Rules • Quantify chiral symmetry breaking via observable spectral functions • Vector (r) - Axialvector (a1) spectral splitting [Weinberg ’67, Das et al ’67] t→(2n+1)p t→(2n)p [ALEPH ‘98, OPAL ‘99] pQCD pQCD • Key features of updated “fit”: [Hohler+RR ‘12] • r+a1 resonance, excited states (r’+a1’), universal continuum (pQCD!)

  7. 2.2.2 Evaluation of Chiral Sum Rules in Vacuum • pion decay • constants • chiral quark • condensates • vector-axialvector splitting (one of the) cleanest observable of • spontaneous chiral symmetry breaking • promising starting point to search for chiral restoration

  8. 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

  9. Outline 2.) Chiral Symmetry Breaking in Vacuum  “Higgs Mechanism”, Condensates + Mass Gap in QCD  Hadron Spectrum, Chiral Partners + Sum Rules 3.) EM Spectral Function in Medium  Hadronic Theory  QGP + Lattice QCD 4.) EM Probes in Heavy-Ion Collisions  Spectro-, Thermo-, Chrono- + Baro-meter  Thermal Photons  Pt Spectra + Collectivity 5.) Conclusions

  10. 3.1 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

  11. p Sp Sp Sp r Sr Sr Sr 3.2 Axialvector in Medium: 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:

  12. 3.3 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?!

  13. 3.3.2 Back to Spectral Function -Im Pem /(C T q0) • suggests approach to chiral restoration + deconfinement

  14. 3.4 Dilepton Rates: Hadronic - Lattice - Perturbative dRee /dM2 ~ ∫d3q f B(q0;T) Im PV dRee/d4q 1.4Tc (quenched) q=0 • 3-fold “degeneracy” toward~Tc • Quark-Hadron Duality at all M?! • ( degenerate axialvector SF) - [qq→ee] [HTL] [Ding et al ’10] [RR,Wambach et al ’99]

  15. 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)

  16. Outline 2.) Chiral Symmetry Breaking in Vacuum  “Higgs Mechanism”, Condensates + Mass Gap in QCD  Hadron Spectrum, Chiral Partners + Sum Rules 3.) EM Spectral Function in Medium  Hadronic Theory  QGP + Lattice QCD 4.) EM Probes in Heavy-Ion Collisions  Spectro-, Thermo-, Chrono- + Baro-meter  Thermal Photons  Pt Spectra + Collectivity 5.) Conclusions

  17. 4.1 Dilepton Rates vs. Exp.: NA60 “Spectrometer” • Evolve rates over fireball expansion: Thermal m+m- Emission Rate Acc.-correctedm+m- Excess Spectra In-In(158AGeV) [NA60 ‘09] Mmm [GeV] [van Hees+RR ’08] • invariant-mass spectrum directly • reflects thermal emission rate!

  18. 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 baryons Mmm [GeV]

  19. 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?!)

  20. 4.3 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 ealry QGP • emission [Holopainen et al ’11,…]

  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! [Turbide et al ’04] [van Hees et al ’11]

  22. 4.3.3 Thermal Photon Spectra + v2: PHENIX thermal + prim. g • both spectral slope and v2 point at • blue-shifted hadronic source… • to be tested in full hydro [van Hees,Gale+RR ’11]

  23. 4.4 QGP Barometer: Blue Shift vs. Temperature RHIC SPS • QGP-flow driven increase of Teff ~ T + M (bflow)2 at RHIC • temperature overcomes flowing late r’s → minimum (opposite to SPS!) • expect to be more pronounced at LHC

  24. 5.) Conclusions:Potential of Thermal EM Radiation • Spectrometer: “prototype” in-medium spectral function, • hadron-to-quark transition • Chiral Restoration: Weinberg + QCD sum rules, • lattice QCD (mB~0!) + perturbative limit • Quality control: rates (constraints, continuity), medium evolution, • consistency SIS-SPS-RHIC-LHC, … • Needed: high-quality data to determine spectral shape, then use • with flow diagnostics • (Non-) Redundancy of RHIC and LHC critical

  25. 4.7 Elliptic Flow Diagnostics (RHIC) [He et al ‘12] • maximum structure due to late r decays [Chatterjee et al ‘07, Zhuang et al ‘09]

  26. 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!)

  27. 2.3.2 NA60 Mass Spectra: pt Dependence Mmm [GeV] • more involved at pT>1.5GeV: Drell-Yan, primordial/freezeout r , …

  28. 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

  29. 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

  30. Outline 2.) Chiral Symmetry Breaking in Vacuum  “Higgs Mechanism”, Condensates + Mass Gap in QCD  Hadron Spectrum, Chiral Partners + Sum Rules 3.) EM Spectral Function in Medium  Hadronic Theory  QGP + Lattice QCD 4.) Highlights of EM Probes in Heavy-Ion Collisions  Spectro-, Thermo-, Chrono- + Baro-meter  Thermal Photons 5.) Low-Mass Dileptons at LHC  Mass Spectra + Collectivity 6.) Conclusions

  31. 5.1 Thermal Dileptons at LHC • charm comparable, accurate (in-medium) measurement critical • low-mass spectral shape in chiral restoration window

  32. 2.2 EM Probes at SPS • all calculated with the same e.m. spectral function! • thermal source: Ti≈210MeV, HG-dominated, r-meson melting!

  33. 2.) Transport: Electric Conductivity • hadronic theories (T~150MeV): • - chiral pert. theory (pion gas): sem / T ~ 0.11 e2 • - hadronic many-body theory: sem / T ~ 0.09 e2 [Fernandez-Fraile+ Gomez-Nicola ’07] • lattice QCD (T ~ (1.5-3) Tc ): • sem /T ~ (0.26±0.02) e2 [Gupta ’04, Aarts et al ’07, Ding et al. ‘11] • soft-photon limit of • thermal emission rate • EM Susceptibility ( → charge fluctuations): • Q2 -Q 2 =χem = Πem(q0=0,q→0)

  34. 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

  35. 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 - -

  36. = = 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”)

  37. 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

  38. 2.3.2 Acceptance-Corrected NA60 Spectra Mmm [GeV] Mmm [GeV] • more involved at pT>1.5GeV: Drell-Yan, primordial/freezeout r , …

  39. 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]

  40. 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

  41. 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)

  42. 4.4.1 Variations in QGP Radiation • improvements in QGP rate insufficient

  43. 4.4.2 Variations in Fireball Properties • variations in space-time evolution only • significant in (late) hadronic phase

  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. 1.2 Intro-II:EoS and Particle Content • Hadron Resonance Gas until close to Tc • - but far from non-interacting: • short-lived resonances R: • a + b → R → a + b,tR ≤ 1 fm/c • Parton Quasi-Particles shortly above Tc • - but large interaction measure I(T) = e -3P  both “phases” strongly coupled (hydro!): - large interaction rates → large collisional widths - resonance broadening → melting → quarks - broad parton quasi-particles - “Feshbach” resonances around Tc (coalescence!)

  46. 2.3.6 Hydrodynamics vs. Fireball Expansion • very good agreement • between original • hydro [Dusling/Zahed] • and fireball [Hees/Rapp]

  47. 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]

  48. 4.2 Low-Mass Dileptons: Chronometer In-In Nch>30 • first “explicit” measurement of interacting-fireball lifetime: • tFB≈ (7±1) fm/c

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