Thermal Photons in Strong Interactions

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Thermal Photons in Strong Interactions
Ralf Rapp Cyclotron Inst. Physics Dept. Texas
AM University College Station, USA College
Station, 24.09.04
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Introduction I E.M. Probes in Strong Interactions

• g-ray spectroscopy of atomic nuclei collective
  phenomena
• DIS off the nucleon - parton model, PDFs
  (high Q2)
• - nonpert.
  structure of nucleon JLAB
• thermal emission - compact stars (?!)
• - heavy-ion
  collisions
• What is the electromagnetic spectrum of
  matter?

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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
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Introduction II Electromagnetic Emission Rates
E.M. Correlation Function
Im ?em(M,q)
Im ?em(q0q)
also e.m susceptibility (charge fluct) ?
?em(q00,q?0)

• In URHICs
• source strength depend. on T, mB, mp medium
  effects,
• system evolution V(t), T(t), mB(t)
  transverse expansion,
• nonthermal sources ee- Drell-Yan,
  open-charm g initial/
• consistency!
  pre-equil.

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2. Thermal Photon Radiation
2.1 Generalities
Emission Rate per 4-volume and 3-momentum
transverse photon selfenergy
many-body language
in-medium effects, resummations,
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2.2 Quark-Gluon Plasma
Naïve Leading Order Processes q q (g) ? g
(q) ?
q
g
q
Kapusta etal 91, Baier etal 92
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2.3.1 Hot Hadronic Matter p-r-a1 Gas
Chiral Lagrangian Axial/Vector-mesons, e.g. HLS
or MYM

• (g0,m0,s,x) fit to mr,a1 , Gr,a1
• D/S and G(a1?p?) not optimal

Song 93, Halasz etal 98,
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2.3.1.b Hadronic Formfactors

• quantitative analysis account for finite
  hadron size
• improves a1 phenomenology
• t-channel exchange gauge invariance nontrivial
  Kapusta etal 91
• simplified approach
  Turbide,GaleRR 04

with
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2.3.2 Further Meson Gas Sources
(i) Strangeness Contributions SU(3)F MYM
25 of pp???
40 of pr?p? !
(iii) Higher Resonances Ax-Vec a1,h1?pg,
Vec w,w,w?pg other p(1300)?pg
f1?rg , K1?Kg K?Kg
a2(1320)?pg
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2.3.3 Baryonic Contributions

• use in-medium r spectral funct
• constrained by nucl. g-absorption

B,a1,K1...
N,p,K
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2.3.3(b) Photon Rates from r Spectral
FunctionBaryons Meson-Resonances

• baryonic contributions
• dominant for q0lt1GeV
• (CERES enhancement!)
• also true at RHICLHC
• at T180MeV, mB0

mB220MeV
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2.3.4 HG Emission Rates Summary

• w t-channel (very) important
• at high energy
• formfactor suppression (2-4)
• strangeness significant
• baryons at low energy

mB220MeV
Turbide,RRGale 04
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2.3.5 In-Medium Effects

• many-body approach encoded in vector-spectral
  function,
• 
  relevant below M , q0 1-1.5 GeV
• dropping masses
• large enhancement due
• to increased phase space
• SongFai 98, Alam etal 03
• unless
• vector coupling decreases
• towards Tc (HLS, a?1)
• HaradaYamawaki 01,
• Halasz etal 98

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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 ?!

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3. Relativistic Heavy-Ion Collisions
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3.1 Nonthermal Sources
Initial hard production pp ? ?X
scaling with xT2pT /vs , power-law fit
Srivastava 01
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3.2 Thermal Evolution QGP? Mix? HG
QGP initial conditions SPS

• t01fm/c ? t00.5fm/c 2-3
• sCdQGT3 dQG40 ? 32 2
• pre-equilibrium?!

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3.3 Comparison to Data I WA98 at SPS
Hydrodynamics QGP HG
Huovinen,RuuskanenRäsänen 02

• T0260MeV, QGP-dominated
• still true if pp?gX included

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3.3 Comp. to Data II WA98 Low-qt Anomaly
Expanding Fireball Model
Turbide,RRGale04

• current HG rate much below
• 30 longer tFB ? 30 increase

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3.3 Perspectives on Data III RHIC
Predictions for Central Au-Au
PHENIX Data

• large pre-equilibrium yield
• from parton cascade (no LPM)
• thermal yields consistent
• QGP undersat. small effect

• consistent with initial only
• disfavors parton cascade
• not sensitive to thermal yet

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4. Photon Emission from Colorsuperconductor
Cold Quark Matter ? (qq) Cooper pairs,
Dqq100MeV mq ms2 u-d-s symmetrically paired
(Color-Flavor-Locking) ? ciral symmetry broken,
Goldstone bosons, mp2 mq2 (10MeV)2
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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, FFs)

• extrapolations into phase transition region
• ? HG and QGP shine equally bright
• deeper reason? lattice calculations?

• phenomenology for URHICs compares favorably
• with existing data
• consistency with dileptons
• much excitement ahead PHENIX, NA60, HADES,
  ALICE,
• and
  theory!

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• Additional Slides

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Photon Properties in Colorsuperconductors
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(i) r(770)
2.2.2 1 Mesons
Constraints - branching ratios B,M?rN,rp - gN,
gA absorpt., pN?rN - QCD sum rules
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2.2.4 In-Medium Baryons D(1232)

• ? long history in nuclear physics ! ( pA , gA
  )
• e.g. nuclear photoabsorption MD, GD up by
  20MeV
• ? little attention at finite temperature
• ? D-Propagator at finite rB and T van
  Hees RR 04

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(i) Check D in Vacuum and in Nuclei
? ok !
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(ii) D(1232) in URHICs
? broadening Bose factor, pD?B ? repulsion
pDN-1, pNN-1
not yet included
(pN?D)
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Comparison of Hadronic Models to LGT
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2.2.6 Observables in URHICs
e e-
?

• (i) Lepton Pairs
  (ii) Photons

Turbide,GaleRR 03

• consistent with dileptons
• pp Brems with soft s at low q?

baryon density effects!