marcus bleicher, tbs berkeley 2005 what have we learned from transport models? marcus bleicher...
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Marcus Bleicher, TBS Berkeley 2005
What have we learned from transport models?
Marcus Bleicher
Institut für Theoretische Physik
Goethe Universität Frankfurt
Germany
Marcus Bleicher, TBS Berkeley 2005
In collaboration with
• Elena Bratkovskaya
• Sascha Vogel
• Xianglei Zhu
• Stephane Haussler
• Hannah Petersen
• Diana Schumacher
Marcus Bleicher, TBS Berkeley 2005
Todays transport/cascade models
• RQMD (the grandfather of relativistic transport models) development stopped around 2000
• UrQMD (development started 1996 at Frankfurt)
• HSD (Giessen group)
• Parton cascades (ZPC, MPC, GPC, SPC aka VNI/B, ….)
NOT transport/cascade models:• HIJING• PYTHIA/FRITIOF• NEXUS, VENUS• DPM
Marcus Bleicher, TBS Berkeley 2005
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
• Generates full space-time dynamics of hadrons and strings
Marcus Bleicher, TBS Berkeley 2005
Included Particles
Marcus Bleicher, TBS Berkeley 2005
Resonance cross sections
Marcus Bleicher, TBS Berkeley 2005
• Initialization of projectile and target (Lorentz contracted Woods-Saxon)• Generate table with collision/decay sequence with
•Propagate to next collision•Perform collision according to cross sections - elastic scattering - inelastic scattering - resonance production - soft string formation and fragmentation - pQCD hard scattering / fragmentation• Update particle arrays, update collision table, perform next collisions
Reaction stages
Marcus Bleicher, TBS Berkeley 2005
Basic checks (I)
Marcus Bleicher, TBS Berkeley 2005
Basic Checks (II)
Unfortunately the data has poor quality
One has to rely on the extrapolation
This leads to ~10% systematic uncertainty
Marcus Bleicher, TBS Berkeley 2005
Baryon Stopping
Energy deposition is OK
Anything special here?
Marcus Bleicher, TBS Berkeley 2005
Particle Production
Extrapolation from pp to AA is OK
Marcus Bleicher, TBS Berkeley 2005
Collision Spectrum
• Initial stage scattering before 1.5 fm/c:Baryon stopping, meson production, may be QGP formation
• Thermalization stage (1.5 – 6 fm/c):Cooking QCD matter
• Hadronic freeze-out stage (6 – 10 fm/c):Elastic and pseudo-elastic hadron scatterings
Pb+Pb @ 160 AGeV
Marcus Bleicher, TBS Berkeley 2005
What can be studied:
• Kinetic observables: longitudinal pressure (Landau or Bjorken?)transverse pressure (radial flow & elliptic flow)
• Chemical observables: Strangeness enhancementFluctuationsResonances
Marcus Bleicher, TBS Berkeley 2005
• 1st Order phase transition at high
•No P.T. at low
• Search for irregularities around Ebeam = 10-40 GeV:
Flow, strangeness, E-by-E
Where do we expect interesting effects?
B
B
Plot adapted from L. Bravina
Marcus Bleicher, TBS Berkeley 2005
AA Excitation functions
• 4 and mid-y abundancies: OK
• Energy dependence: OK
• Hadron-string models work well
Marcus Bleicher, TBS Berkeley 2005
Check for strangeness enhancement compared to pp
•Strangeness enhancement is strongest at low energies
•Apparent Lambda enhancement from stopping
•Disappearance of canonical suppression
Marcus Bleicher, TBS Berkeley 2005
Excitation functions: ratios
• ‘Horn’ in the ratio not reproduced
• well reproduced
• relative strange baryon enhancement reproduced
/K
/K
/
Marcus Bleicher, TBS Berkeley 2005
Transverse Pressure:Proton-Proton
• PP works well
• pQCD needed at RHIC
• PYTHIA included in
UrQMD 2.x and HSD
Marcus Bleicher, TBS Berkeley 2005
Proton-Nucleus
• pA is well under control
• CC and SiSi are also under control
• What about AA?
Marcus Bleicher, TBS Berkeley 2005
Transverse mass spectra
• Standard UrQMD and HSD underestimate the data
• Additional resonances of 2-3 GeV mass may improve the description
Marcus Bleicher, TBS Berkeley 2005
Inverse slope systematics
• High mass resonances improve the description at low and high energies
• Cronin effect at high energies improves RHIC results
• How can we test those scenarios?
Marcus Bleicher, TBS Berkeley 2005
Hints from elliptic flow
• High mass resonances can not explain scaled v2 above 40 AGeV
• Data shows saturation of scaled v2
• Strong hint for large pressure and short mean free paths in the early stage of the reaction already from 30 AGeV on !
Data for h-
Marcus Bleicher, TBS Berkeley 2005
Elliptic flow (I)
From Xianglei Zhu
•Elliptic flow from string/hadron model is too small
• However, half of v2 is generated in the hadronic stage
Marcus Bleicher, TBS Berkeley 2005
Elliptic flow (II)
From Xianglei Zhu
•Qualitatively non-flow contributions are reproduced
•Large difference between real v2 and 2-particle cumulants
Marcus Bleicher, TBS Berkeley 2005
Elliptic flow (III)
From Xianglei Zhu
•Hadron/String dynamics predicts correct mass ordering
Marcus Bleicher, TBS Berkeley 2005
Elliptic flow (IV)
From Xianglei Zhu
• Scaling with nq is present in transport calculations
• Scaling is not a unique QGP signal!
Marcus Bleicher, TBS Berkeley 2005
Summary: or What I learned
Transport models produce to few pressure in the early stage above 30 GeV
However, at RHIC up to 50% of v2 are from hadronic stage
mass ordering is correct
non-flow correlations are correct