Thermal Photons in Strong Interactions Ralf Rapp Cyclotron

Thermal Photons in Strong Interactions Ralf Rapp Cyclotron Inst. + Physics Dept. Texas A&M University College Station, USA College Station, 24. 09. 04

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 Q 2) - nonpert. structure of nucleon [JLAB] • thermal emission: - compact stars (? !) - heavy-ion collisions What is the electromagnetic spectrum of matter? c. PT many-body (2 ↔ 2) consistent 0 0. 05 120 ½r 0 degrees of freedom? QGP (3 -body, . . . ) extrapolate 0. 3 150 -160 2 r 0 0. 75 175 5 r 0 (resonances? ) p. QCD e[Ge. Vfm-3] T [Me. V] rhadron

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

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

2. Thermal Photon Radiation 2. 1 Generalities Emission Rate per 4 -volume and 3 -momentum T Im Πem(q 0=q) many-body language: p γ r transverse photon selfenergy cut kinetic theory: p γ r p in-medium effects, resummations, … 2 |M|2

2. 2 Quark-Gluon Plasma “Naïve” Leading Order Processes: q + q (g) → g (q) + γ q q g [Kapusta etal ’ 91, Baier etal ’ 92] But: other contributions to O(αs) collinear enhanced Dg=(t-m. D 2)-1 ~ 1/αs Bremsstrahlung Pair-ann. +scatt. + ladder resummation (LPM) [Aurenche etal ’ 00, Arnold, Moore+Yaffe ’ 01]

2. 3. 1 Hot Hadronic Matter: p-r-a 1 Gas Chiral Lagrangian + Axial/Vector-mesons, e. g. HLS or MYM: • (g 0, m 0, s, x) fit to mr, a 1 , Gr, a 1 D/S and G(a 1→pγ) not optimal [Song ’ 93, Halasz etal ’ 98, …] HLS MYM Kap. ’ 91 (no a 1) • Photon-producing reactions: p γ p p r r γ p, a 1 p mostly at dominant (q 0>0. 5 Ge. V) q 0<0. 5 Ge. V a 1 -strength problematic p, a 1 gauge invariance!

2. 3. 1. b Hadronic Formfactors • quantitative analysis: account for finite hadron size • improves a 1 phenomenology • t-channel exchange: gauge invariance nontrivial [Kapusta etal ’ 91] simplified approach: [Turbide, Gale+RR ’ 04] with Factor 3 -4 suppression at intermediate and high photon energies

2. 3. 2 Further Meson Gas Sources (i) Strangeness Contributions: SU(3)F MYM p γ K K* ~25% of pp→ργ (ii) w t-Channel [Turbide, Gale +RR ’ 04] p K* p w r γ p p γ K ~40% of pr→pγ ! Gwrp large! potentially important … (iii) Higher Resonances Ax-Vec: a 1, h 1→pg, Vec: f 1→rg , K 1→Kg w, w’’→pg other: p(1300)→pg K*→Kg a 2(1320)→pg

2. 3. 3 Baryonic Contributions • use in-medium r –spectral funct: • constrained by nucl. g-absorption: r Sp Sp B*, a 1, K 1. . . > N, p, K… g N → p N, D g N → B* > [Urban, Buballa, RR+Wambach ’ 98] g. N g. A p-ex

2. 3. 3(b) Photon Rates from r Spectral Function: Baryons + Meson-Resonances • baryonic contributions dominant for q 0<1 Ge. V (CERES enhancement!) • also true at RHIC+LHC: m. B=220 Me. V at T=180 Me. V, m. B=0

2. 3. 4 HG Emission Rates: Summary • w t-channel (very) important at high energy • formfactor suppression (2 -4) • strangeness significant m. B=220 Me. V [Turbide, RR+Gale ’ 04] • baryons at low energy

2. 3. 5 In-Medium Effects • many-body approach: encoded in vector-spectral function, relevant below M , q 0 ~ 1 -1. 5 Ge. V • “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]

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” ? ! • Similar findings for thermal dilepton rates not yet understood …

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

3. 1 Nonthermal Sources Initial hard production: pp → γX Nuclear Effects: p. A → g. X scaling with x. T=2 p. T /√s , + power-law fit [Srivastava ’ 01] • “Cronin”: gaussian kt-smear. • cf. p. A → πX • AA: <Dkt 2>AA≈ 2<Dkt 2>p. A

3. 2 Thermal Evolution: QGP→ Mix→ HG HG: chemistry and trans. chemistry [LHC]flow T [Ge. V] QGP: initial conditions [SPS] • t 0=1 fm/c → t 0=0. 5 fm/c: ~2 -3 • s=Cd. QGT 3; d. QG=40 → 32: ~2 • pre-equilibrium? ! • R~exp(3 mp) for pg , … • conserved BB pr use→entropy • yield up at of lowmqpt>0 , down above • build-up (Np=const) • large blue shiftcooling from coll. flow • accelerated

3. 3 Comparison to Data I: WA 98 at SPS Hydrodynamics: QGP + HG [Huovinen, Ruuskanen+Räsänen ’ 02] • T 0≈260 Me. V, QGP-dominated • still true if pp→g. X included Expanding Fireball + Initial [Turbide, RR+Gale’ 04] • initial+Cronin at qt >1. 5 Ge. V T 0=205 Me. V suff. , HG dom.

3. 3 Comp. to Data II: WA 98 “Low-qt Anomaly” Expanding Fireball Model [Turbide, RR+Gale’ 04] • current HG rate much below • 30% longer t. FB 30% increase Include pp→ppg S-wave • slight improvement • in-medium “s” or D ? !

3. 3 Perspectives on Data III: RHIC Predictions for Central Au-Au • large “pre-equilibrium” yield from parton cascade (no LPM) • thermal yields ~ consistent • QGP undersat. small effect PHENIX Data • consistent with initial only • disfavors parton cascade • not sensitive to thermal yet

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

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, NA 60, HADES, ALICE, … and theory!

Additional Slides

Photon Properties in Colorsuperconductors

r Sp Sp B*, a 1, K 1. . . + N, p, K… (i) r(770) > > 2. 2. 2 1± Mesons: Significance of high r. B at low M Constraints: - branching ratios B, M→r. N, rp - g. N, g. A absorpt. , p. N→r. N - QCD sum rules Elab=20 -40 AGe. V optimal? !

2. 2. 4 In-Medium Baryons: D(1232) long history in nuclear physics ! ( p. A , g. A ) e. g. nuclear photoabsorption: MD, GD up by 20 Me. V little attention at finite temperature D-Propagator at finite r. B and T in-medium p-cloud, (1+ f p - f N) > > + > DN-1 > D Sp NN-1 [van Hees + RR ’ 04] > vertex corrections incl. g’ (“induced interaction”) + + . . . > p. D→N(1440), N(1520), D(1600) thermal p-gas

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

(ii) D(1232) in URHICs broadening: Bose factor, p. D→B repulsion: p. DN-1, p. NN-1 not yet included: (p. N→D)

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

2. 2. 6 Observables in URHICs (i) Lepton Pairs e+ e. Im Πem(M, q) γ (ii) Photons Im Πem(q 0=q) [Turbide, Gale+RR ’ 03] baryon density effects! • consistent with dileptons • pp Brems with soft s at low q?