HADES versus DLS: no puzzle anymore

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HADES versus DLS  no puzzle anymore !
Elena Bratkovskaya 22.10.2007 , Workshop
Bremsstrahlung in dilepton production GSI,
Darmstadt
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10 years of DLS puzzle

• DLS-puzzle (since 1997)
• new (1997) DLS data for CC and CaCa at 1.04 A
  GeV are higher than the old (1995) DLS data by
  a factor of 5-7 at 0.15ltMlt0.5 GeV
• Transport models
• good description of pp and pd data from 1 to 5
  GeV
• missing yield at 0.15 lt M lt 0.5 GeV for CC and
  CaCa at 1.04 A GeV
• (similar results obtained by HSD 97 ,
• UrQMD98 and Tübingen QMD03)

10 years of waiting for HADES
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A decade of search for the solution of the DLS
puzzle

• Constraints on p, h by TAPS data
• HSD good description of TAPS data
• on p, h multiplicities and mT-spectra
• gt p (D), h dynamics under control !
• Other channels r, w
• accounting for in-medium effects (collisional
  broadening of vector meson spectral functions,
  dropping vector meson masses) does not provide
  enough enhancement at intermediate M
• contribution from N(1520)
• (E.B.C.M. Ko, PLB 445 (1999) 265)
• and higher baryonic resonances are small (cf. Gy.
  Wolf et al., PRC67 (2003) 044002)
• Also
• accounting for anisotropies in ee-
• emission gives only a small effect

HSD98
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DLS versus HADES
Experiment No contradiction between DLS and
HADES ! What about theory ?
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Dileptons from transport models

• HSD
• UrQMD 1.3 (1998)
• UrQMD 2.2 (2007) (Frankfurt)
• RQMD (Tübingen)
• IQMD (Nantes)
• BRoBUU (Rossendorf)

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Basic concept of HSD

• HSD Hadron-String-Dynamics transport approach
• for each particle species i (i N, R, Y, p, r,
  K, ) the phase-space density fi follows the
  transport equations
• with collision terms Icoll describing
• elastic and inelastic hadronic reactions
• baryon-baryon, meson-baryon, meson-meson
• formation and decay of baryonic and mesonic
  resonances
• string formation and decay (for inclusive
  particle production
• BB -gt X , mB -gtX, X many particles)
• implementation of detailed balance on the level
  of 1lt-gt2
• and 2lt-gt2 reactions ( 2lt-gtn multi-particle
  reactions in HSD)
• off-shell dynamics for short-lived states

BB lt-gt BB, BB lt-gt BBm mB lt-gt mB, mB lt-gt B
Baryons B(p, n, D(1232), N(1440), N(1535),
...) Mesons m(p, h, r, w, f, ...)
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Dilepton channels in HSD

• All particles decaying to dileptons are first
  produced in BB, mB or mm collisions

• Factorization of diagram in the transport
  approach

• The dilepton spectra are calculated
  perturbatively with the time integration method.

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Time integration method for dileptons
Reality
e
only ONE ee- pair with probability
Br(r-gtee-)4.5 .10-5
r
r
w
e-
Virtual time integ. method
t0
tabs
e
r
time
e-
tF
Calculate probability P(t) to emit an ee- pair
at each time t and integrate P(t) over time! r
t0 lt t lt tabs w t0 ltt lt infinity
tF final time of computation in the code t0
production time tabs absorption (or hadronic
decay) time
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The time integration method for dileptons in HSD
Dilepton emission rate
e
r
e-
t00
time
tF
Dilepton invariant mass spectra
tF lt t lt infinity
0 lt t lt tF
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NN bremsstrahlung - SPA
Phase-space corrected soft-photon cross section
Soft-Photon-Approximation (SPA)
N N -gt N N ee-
quasi- elastic N N -gt N N
elastic NN
off-shell correction factor
SPA implementation in HSD ee- production in
elastic NN collision with probability
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NN bremsstrahlung OBE-model
KaptariKämpfer, NPA 764 (2006) 338
OBE-model N N -gt N N ee-
post
pre
pre
post
gauge terms
The strategy to restore gauge invariance is model
dependent!
charged meson exchange
contact terms (from formfactors)
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Bremsstrahlung a new view on an old story

• New OBE-model (KaptariKämpfer, NPA 764 (2006)
  338)
• pn bremstrahlung is larger by a factor of 4 than
  it has been
• calculated before (and used in transport
  calculations)!
• pp bremstrahlung is smaller than pn, however,
  not zero consistent with the 1996 calculations
  from de Jong in a T-matrix approach

2007 (era of HADES) The DLS puzzle is solved by
accounting for a larger pn bremsstrahlung !!!
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HSD Dileptons from pp and pd - DLS

• bremsstrahlung is the dominant contribution in
  pd for 0.15 lt M lt 0.55 GeV at 1-1.5 A GeV

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HSD Dileptons from AA at 1 A GeV - DLS

• bremsstrahlung and D-Dalitz are the dominant
  contributions in AA for 0.15 lt M lt 0.55 GeV at 1
  A GeV !

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HSD Dileptons from CC at 1 and 2 A GeV - HADES
Preliminary HADES data

• HADES data show exponentially decreasing mass
  spectra
• Data are better described by in-medium scenarios
  with collisional broadening
• In-medium effects are more pronounced for heavy
  systems such as AuAu

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HSD Dilepton pT and y spectra from CC at 1 A
GeV - HADES
Preliminary HADES data

• HSD predictions for pT and y spectra are in good
  agreement
• with the HADES data for all M-bins!

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HSD Dilepton pT and y spectra from CC at 2 A
GeV - HADES
Mlt0.15 GeV/c2
Mgt0.55 GeV/c2
0.15ltMlt0.55 GeV/c2
Preliminary HADES data

• HSD predictions for pT and y spectra are in good
  agreement
• with the HADES data for all M-bins!

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Bremsstrahlung in UrQMD 1.3 (1998)
Ernst et al, PRC58 (1998) 447
SPA
Bremsstrahlung-UrQMD98 smaller than
bremsstrahlung-Kaptari06 by a factor of 3-6
SPA implementation in UrQMD (1998) ee-
production in elastic NN collisions (similar to
HSD)
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Dileptons from pp and pd - UrQMD 1.3
Ernst et al, PRC58 (1998) 447

• old bremsstrahlung missing yield for pd at
  0.15 lt M lt 0.55 GeV at 1-1.5 A GeV

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Dileptons from AA - UrQMD 1.3
Ernst et al, PRC58 (1998) 447

• old bremsstrahlung missing yield for AA at
  0.15 lt M lt 0.55 GeV at 1 A GeV
• (consistent with HSD with old SPA)

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Dileptons from AA - UrQMD 2.2 (2007)
D. Schumacher, S. Vogel, M. Bleicher, Acta
Phys.Hung. A27 (2006) 451
NO bremsstrahlung in UrQMD 2.2
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Dileptons from pp and pd - RQMD (Tübingen)
C. Fuchs et al., Phys. Rev. C67 025202(2003)

• NO bremsstrahlung missing yield for pd at
  0.15 lt M lt 0.55 GeV at 1-1.5 A GeV

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Dileptons from AA - RQMD (Tübingen)
C. Fuchs et al., Phys. Rev. C67 025202(2003)
HADES - RQMD07
DLS - RQMD03
1 A GeV

• NO bremsstrahlung in RQMD
• too strong D-Dalitz contribution (since no time
  integration?)

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Bremsstrahlung in IQMD (Nantes)
M. Thomere, C. Hartnack, G. Wolf, J. Aichelin,
PRC75 (2007) 064902
HADES CC, 2 A GeV
SPA implementation in IQMD (?) ee- production
in each NN collision (i.e. elastic and inelastic)
!? - differs from HSD and UrQMD98 (only elastic
NN collisions are counted!)
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Bremsstrahlung in BRoBUU (Rossendorf)
H.W. Barz, B. Kämpfer, Gy. Wolf, M. Zetenyi,
nucl-th/0605036
SPA implementation in BRoBUU (?) ee-
production in each NN collision (i.e. elastic and
inelastic) ! - similar to IQMD (Nantes)
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Test in HSDbremsstrahlung production in NN
collisions (only elastic vs. all)
In HSD assume ee- production from old SPA
bremsstrahlung in each NN collision (i.e. elastic
and inelastic reactions) gt can reproduce the
results by Gy. Wolf et al., i.e. IQMD (Nantes)
and BRoBUU (Rossendorf) !
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Summary Bremsstrahlung in transport models

• Transport models give similar results ONLY with
  the same
• initial input !
• gt REQUESTS
• unification of the treatment of dilepton
  production in transport models
• Similar cross sections for elementary channels
• Time-integration method for dilepton production
• Off-shell treatment of broad resonances
• Consistent microscopic calculations for ee-
• bremsstrahlung from NN and mN collisions!

We need clear separation of the individual
contributions in a form applicable in transport
codes, e.g. many-dimensional matrix (or
parametrization) for ds/dMdydpT (s,M,y,pT )
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Summary
HADES succeeded the DLS puzzle is solved !
Outlook need new pp and pd data from HADES for a
final check!