Dileptons in HeavyIon Collisions

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Dileptons in Heavy-Ion Collisions
Ralf Rapp Cyclotron Institute Physics
Department Texas AM University College
Station, USA HIC4FAIR Workshop on Dense Matter
in Heavy-Ion Collisions and Supernovae Prerow,
10.-14.10.09
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1.) Intro-I Probing Strongly Interacting Matter

• Electromagnetic Probes
• penetrating lEM gtgt Rnuc
• Equilibrium
• EM spectral function
• Im PEM(q0,qmB,T)

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1.2) Intro-II Low-Mass Dileptons at CERN-SPS
CERES/NA45 2000
NA60 2005
mee GeV

• strong excess around M 0.5GeV (and M gt 1GeV )
  
• little excess in r, w, f region

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Outline
1.) Introduction 2.) Chiral Symmetry Vector
Mesons ? EM Emission and Vector Mesons ?
Chiral Symmetry Breaking ? r and a1 Meson
in Medium 3.) Dilepton Spectra at in A-A and g-A
? Thermal Emission and NA60 (SPS) ?
Photoproduction and CLAS (TJNAF) 4.) Conclusions
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2.1 Thermal Electromagnetic Emission
EM Current-Current Correlation Function
Thermal Dilepton and Photon Production Rates
Im ?em(M,q)
Im ?em(q0q)
r -meson dominated
ImPem ImDr ImDw /10 ImDf /5
Low Mass
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2.2 Chiral Symmetry QCD Vacuum
isospin chiral (left/right-handed)
invariant
But Higgs Mechanism in Strong Interactions qq
attraction ? Bose condensate fills QCD vacuum
Spontaneous Chiral Symmetry Breaking
-
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2.3 Hadron Spectra Chiral Symm. Breaking
Axial-/Vector Correlators
Constituent Quark Mass
Data lattice Bowman et al 02 Theory
Instanton Model DiakonovPetrov Shuryak 85
pQCD cont.

• Weinberg Sum Rule(s)

? chiral breaking q2 1 GeV2
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2.4 r-Meson in Medium Hadronic Interactions
Chanfray et al, Herrmann et al, RR et al, Koch
et al, Weise et al, Mosel et al, Eletsky et al,
Oset et al, Lutz et al
Dr (M,qmB ,T) M 2 - mr2 - Srpp - SrB - SrM
-1
r-Propagator
B,a1,K1...
Sp
r
r
SrB,rM
Srpp
Selfenergies
N,p,K
Sp
Constraints decays B,M? rN, rp, ...
scattering pN ? rN, gA,
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2.5 Axialvector in Medium Dynamical a1(1260)
p

a1 resonance
. . .
Vacuum
r

In Medium
. . .

• in-medium p r propagators
• substantial broadening of
• p-r scattering amplitude
• consequences for chiral
• restoration to be elaborated

Cabrera,Jido,RocaRR 09 in preparation
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3.) Dilepton Spectra in A-A and g-A
Thermal Dilepton Emission Rate
e e-
g
Im ?em(M,qmB,T)
Im ?em Im Dr
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3.1 Dilepton Rates Hadronic vs. QGP
dRee /dM2 ?d3q f
B(q0T) Im Pem

• Hard-Thermal-Loop Braaten et al 90
• enhanced over Born rate
• Hadronic and QGP rates
• degenerate around Tc
• Quark-Hadron Duality at all M ?!
• (? degenerate axialvector SF!)

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3.2 Dilepton Excess Spectra at SPS
Thermal Emission Spectrum

• average Gr (T150MeV) 350-400 MeV
• ? Gr (TTc) 600 MeV ? mr
• fireball lifetime tFB (6.51) fm/c

van HeesRR 06, Dusling et al 06, Ruppert et
al 07, Bratkovskaya et al 08
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3.2.2 NA60 Data vs. In-Medium Dimuon Rates
Mmm GeV
van Hees RR 07
RR,Wambach et al 99

• acceptance-corrected data directly reflect
  thermal rates!

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3.3 r Meson in Cold Nuclear Matter
Nuclear Photo-Production
r
e e-
g
invariant mass spectra
g A ? ee- X
CLAS/JLab 08
Theoretical Approach
Riek et al 08
in-medium r spectral function
elementary production amplitude

Fe - Ti
rN 0.5 r0
r
g
N
Mee GeV
M GeV
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4.) Conclusions

• Electromagnetic Probes
• - study matter properties in nuclear reactions
• - low mass in-medium vector mesons
• Chiral Symmetry Breaking (Restoration)
• - chiral partners r - a1 (degeneracy at Tc)
• Thermal Dilepton Rates
• - melting r toward Tc (quark-hadron duality?)
  
• Dilepton Spectra
• - quantitative agreement at SPS
• - ok at TJNAF (g-A)
• - failure at RHIC thus far

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3.2.2 Low-Mass Dileptons at RHIC PHENIX

• Successful approach at SPS fails at RHIC

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4.5 EM Probes in Central Pb-Au/Pb at SPS
Di-Electrons CERES/NA45
Photons WA98

• updated fireball (aT0.045?0.085/fm)
• very low-mass di-electrons ? (low-energy) photons

van HeesRR 07
Srivastava et al 05, LiuRR 06
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4.8 Axialvector in Medium Explicit a1(1260)
D,N(1900)
Sp
Sp
a1

. . .
N-1
Sr
N(1520)
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5.2.3 NA60 Dimuons Sensitivity to QGP and Tc

• vary critical and chemical-freezeout temperature
  (Tfo fix)

EoS-B
EoS-C

• overall shape of spectra robust duality of
  dilepton rate around Tc!
• yields slightly larger for large Tc (hadronic
  volume!), Dt lt 1fm/c
• intermediate mass (Mgt1GeV) QGP vs. hadronic
  depends on Tc

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2.5 Cold Nuclear Matter r Photo-Production
g A ? ee- X
CLAS/JLab GiBUU 08
Eg1.5-3 GeV
Fe -Ti
rN 0.5 r0
Riek et al 08
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2.6 Sum Rules and Order Parameters

• QCD-SRs

HatsudaLee 91, AsakawaKo 92, Klingl et al
97, Leupold et al 98, Kämpfer et al 03,
Ruppert et al 05

• Weinberg-SRs moments Vector-Axialvector

Weinberg 67, Das et al 67, KapustaShuryak
93
? Promising synergy of lQCD and effective models
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2.3.2 Acceptance-Corrected NA60 Spectra
Mmm GeV
Mmm GeV

• more involved at pTgt1.5GeV Drell-Yan,
  primordial/freezeout r ,

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X.) Example for Comprehensive Analysis NA60
Dileptons
Charmonium Flow
Charmonium Production
? thermal medium radiating from around Tc with
melted r , well-bound J/y with large
collectivity
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2.4 r Spectral Function at Lower Collision
Energies

• largest sensitivity for M 0.4 GeV - soft
  modes!
• Critical point s - wL mixing (q?0) with ms? 0,
• but w ? ee- signal (too) weak