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Transport Model Analysis of UltraRelativistic AA interactions

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Stephane Haussler. Hannah Petersen. Diana Schumacher. Marcus Bleicher, APFB05, SUT Thailand ... via AQM or calculated by detailed balance. pQCD hard scattering ... – PowerPoint PPT presentation

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Title: Transport Model Analysis of UltraRelativistic AA interactions


1
Transport Model Analysis of Ultra-Relativistic
AA interactions
  • Marcus Bleicher
  • Institut für Theoretische Physik
  • Goethe Universität Frankfurt
  • Germany

2
Thanks to
  • Elena Bratkovskaya
  • Sascha Vogel
  • Xianglei Zhu
  • Stephane Haussler
  • Hannah Petersen
  • Diana Schumacher

3
Contents
  • Introduction
  • Strangeness as QGP signal
  • Experimental facts the horn
  • Strange fluctuations
  • Summary

4
The tool UrQMDv2.2
  • Non-equilibrium transport model
  • Hadrons and resonances
  • String excitation and fragmentation
  • Cross sections are parameterized
  • via AQM or calculated by detailed balance
  • pQCD hard scattering at high energies (not in
    v1.3)
  • Generates full space-time dynamics of hadrons
    and strings

5
Collision Spectrum
1fm/c
10fm/c
  • Initial stage scattering before 1.5 fm/c
    Baryon stopping, meson production,
  • Thermalization stage (1.5 6 fm/c) Cooking
    QCD matter, may be QGP formation
  • Hadronic freeze-out stage (6 10 fm/c)
    Elastic and pseudo-elastic hadron scatterings

PbPb _at_ 160 AGeV
6
Where do we expect QGP?
  • 1st Order phase transition at high
  • No P.T. at low
  • Search for irregularities around Ebeam 10-40
    GeV
  • Flow, strangeness, E-by-E

Plot adapted from L. Bravina
7
Strangeness enhancement
T0.2-0.3 GeV
? QGP has lower threshold for strangeness
production ? relative strangeness enhancement
8
PP Excitation functions
  • PP works nicely
  • Perturbative QCD is used for hard scatterings
    above 50 GeV

9
AA Excitation functions
  • 4 and mid-y abundancies OK
  • Energy dependence OK
  • Hadron-string models work well

10
Excitation functions ratios
  • Horn in the ratio not reproduced
  • well reproduced
  • relative strange baryon
    enhancement reproduced

11
Fluctuation studies Ratios
Taken from Christoph Roland
NA49 Preliminary
NA49 Preliminary
  • K/p fluctuations increase towards lower beam
    energy
  • Significant enhancement over hadronic cascade
    model
  • p/p fluctuations are negative
  • indicates a strong contribution from resonance
    decays

12
Baryon-Strangeness Correlations I
Definition
Idea Strangeness and baryon numbercarriers are
different in QGP and hadron gas.
First suggested by V. Koch et al., 2005
  • HG strangeness is decoupled from baryon number
    (mesons) ? small CBS correlation
  • QGP strangeness is fixed to baryon number
    (strange quark)? large CBS correlation

13
Baryon-Strangeness Correlations 2
  • Limiting cases for CBS
  • Large mB CBS ?3/2
  • large acc. window CBS ?0Explored with help
    of increasing rapidity window inAuAu reaction
    at RHIC
  • Present models yield similar results for small
    rapidity window
  • Different handling of the fragmentation
    region/spectators influences results at large
    rapidities

14
Baryon-Strangeness Correlations 3
Energy dependence of CBS allows to study the
onset of deconfinement transition Note that the
QGP result is for m0 Here ymaxlt0.5
  • Deviations from the HG are expected around high
    SPS energy region, due to QGP onset.

15
Baryon-Strangeness Correlations 4
Centrality dependence of CBS allows to study the
critical volume needed for QGP formation. Note
that the QGP result is for m0 ymaxlt0.5,
Ecm200AGeV
  • Hadron-string transport models predict no
    centrality dependence of CBS
  • A QGP transition leads to a strong centrality
    dependence

16
Summary
  • Hadron yields are well reproduced in models
  • Most ratios can be understood in transport
    models
  • Model K/p ratios do not reproduce the strong
    peak observed in data
  • In data, the dynamical fluctuation of K/p
    increase strongly towards 20 AGeV beam energy
    (not present in hadron-string models)
  • Baryon-strangeness correlations allow to pin
    down the onset of the QGP transition.

17
Conclusion
Most interesting energy range, because
  • K/p ratio enhanced
  • Large dynamical fluctuations
  • Latent heat is big

Will be explored by new GSI accelerator (near
Frankfurt)
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