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Critical Enhancement of Thermal Photons

Critical Enhancement of Thermal Photons. Ralf Rapp Cyclotron Institute + Dept of Phys & Astro Texas A&M University College Station, USA With: H. van Hees (FIAS), Min He (Nanjing) 24 th International Conference on Ultrarelativistic Nucleus-Nucleus Collisions

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Critical Enhancement of Thermal Photons

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  1. Critical Enhancement of Thermal Photons Ralf Rapp Cyclotron Institute + Dept of Phys & Astro Texas A&M University College Station, USA With: H. van Hees (FIAS), Min He (Nanjing) 24th International Conference on Ultrarelativistic Nucleus-Nucleus Collisions Darmstadt (Germany), 18.-24.05.14

  2. 1.) Direct Photon “Puzzle” • Large enhancement • Soft slope • Large v2 • Low-mass Dileptons: • Universal source SPS → RHIC • Radiation around Tpc ~ 160MeV • M→0 limit!?

  3. 1.2 Phenomenology of Thermal Photons • Medium evolution: • Fireball or hydro • Emission rates: • Hadronic matter • QGP

  4. > 2 p γ r p 2.1 Thermal Photon Rates I: Hadronic Matter • Thermal Field Theory: N D [RUBW ’99] p B r p N-1 p Sp N -1 g B p N → gD N NN → gND • Kinetic Theory: pr a1KK* |M|2 [TRG ’04]

  5. 2.2 Thermal Photon Rates II: Quark-Gluon Plasma • “AMY-QGP”: complete LO rates (resummed perturbative) [Arnold,Moore+Yaffe ’01] q q g

  6. 2.3 Thermal Rate Summary no bar. • r spectral function dominates hadronic for q0 ≤ 1 GeV (q0lab ≤ 2GeV) • total hadronic ≈ LO QGP

  7. 3.) Bulk-Medium Evolution: Fireball vs. Hydro Pions + Protons f Mesons Tfo=160MeV Tfo=110MeV • lattice-EoS (Tpc~170MeV) + hadronic phase (Tch=160MeV) • multi-strange freezeout at Tch→ bulk-v2 saturates at Tch [He et al ’11, Hees et al `11]

  8. 4.1 Direct Photons I: RHIC Fireball Ideal Hydro • similar QGP, larger hadronic yield in fireball • largest emission around Tpc [van Hees, He+RR ’14]

  9. 4.1.2 Emission Characteristics Temperature Profile Fraction of Matter with T>Tfo Fireball Hydro Sactive / Stot t-t0 [fm/c] • Gradual freeze-out in hydro, cells never re-thermalize

  10. 4.2 Direct Photons II: LHC Fireball Hydro • increased QGP part → closer agreement fireball - hydro

  11. 4.3 Enhanced Photon Rates in Hydro • upscale photon rates by factor of 2, up to 3 for Tpc ± 30MeV RHIC LHC • getting close(r) to the data (more so with fireball)

  12. 5.) Conclusions • Thermal photon spectra with: • - LO-QGP + (r SF + meson exchange) • - Medium evol. with sequential f.o. → bulk-v2saturates at ~Tpc • - Radiative final-state decays •  Not (very) far from spectra + v2 data • Possible need for enhanced rate (natural around Tpc)

  13. 4.x Collective Flow Effect on Spectra Rate in Rest Frame Spectrum in Lab Frame q0lab [GeV] q0* [GeV] • Doppler shift q0lab ~ 2 q0* = 2 qlab ∙ u

  14. 4.x Effective Slope Parameters First-Order EoS (Tc=180MeV) Lattice EoS (Tpc=170MeV) [van Hees,Gale+RR ’11] [van Hees,He+RR ’14] • local temperatures T≤ 200MeV

  15. 4.x Decomposition of Hadronic Contribution Spectral Yields Elliptic Flow • r spectral function contribution appreciable

  16. 3.5 Collectivity of Dileptons: Blue Shift and v2 SPS RHIC • QGP-flow “arm” (M > 1GeV) rises at RHIC: Teff ~ T + M (bflow)2 • high pt: slope saturates at initial temperature T0 • v2 develops maximum at r mass! [He et al in prep]

  17. 3.2 Excitation Function: SPS - RHIC Pb-Au(8.8GeV) Au-Au (20-200GeV) QM12 Pb-Au(17.3GeV) • consistent excess emission source • suggests “universal” medium effect around Tpc • FAIR, LHC? [cf. also Bratkovskaya et al, Alam et al, Bleicher et al, Wang et al …]

  18. 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

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