Marcus Bleicher, CCAST- Workshop 2004 Strangeness Dynamics and Transverse Pressure in HIC Marcus...
-
Upload
amie-jenkins -
Category
Documents
-
view
222 -
download
1
Transcript of Marcus Bleicher, CCAST- Workshop 2004 Strangeness Dynamics and Transverse Pressure in HIC Marcus...
Marcus Bleicher, CCAST- Workshop 2004
Strangeness Dynamics andTransverse Pressure in HIC
Marcus Bleicher
Institut für Theoretische Physik
Goethe Universität Frankfurt
Germany
Marcus Bleicher, CCAST- Workshop 2004
Contents
• Chemical equilibrium stage:
The ‘horn’, the ‘step’
• Kinetic decoupling stage:
Resonance (non-) suppression
• Summary
Marcus Bleicher, CCAST- Workshop 2004
The tool: UrQMD
• Non-equilibrium transport model
• Hadrons and resonances
• String excitation and fragmentation
• Cross sections are parametrizedvia AQM or calculated by detailed balance
• Generates full space-time dynamics of hadrons and strings
Marcus Bleicher, CCAST- Workshop 2004
Part I: Evidence for the tri-critical point?
B
• 1st Order phase transition at high
•No P.T. at low
• Search for irregularities around Ebeam = 10-40 GeV:
Flow, strangeness, E-by-E
B
Marcus Bleicher, CCAST- Workshop 2004
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, CCAST- Workshop 2004
Excitation functions
4 and midrapidity abundancies: OK
Energy dependence: OK
Hadron-string models work well
Marcus Bleicher, CCAST- Workshop 2004
Excitation functions: ratios
• ‘Horn’ in the ratio not reproduced
• well reproduced
• relative strange baryon enhancement reproduced
/K
/K
/
Marcus Bleicher, CCAST- Workshop 2004
Ratio excitation functions: Summary
• Yields are well reproduced
• Most ratios can be understood in transport models
• Model K/pi ratio does not reproduce the strong peak observed in data
Marcus Bleicher, CCAST- Workshop 2004
Proton-Proton
• PP works well
• pQCD needed at RHIC
• PYTHIA included in
UrQMD 2.x and HSD
Marcus Bleicher, CCAST- Workshop 2004
Transverse mass spectra
• Standard UrQMD and HSD underestimate the data
• Additional resonances from 2-3 GeV do improve the description (UrQMD 2.1)
Marcus Bleicher, CCAST- Workshop 2004
Inverse slope systematics
• Standard transport models fail
• What is missing?
• Maybe high mass resonanceslike in UrQMD 2.1
• Maybe QGP pressure…
Marcus Bleicher, CCAST- Workshop 2004
Phase diagram• QGP might be reachedalready at 11 GeV!
• Tricritical point at 10-40 GeV
• No phase transition at RHIC
• Necessary to explore low energy region to study the phase transition
Marcus Bleicher, CCAST- Workshop 2004
Flow excitation functions: Summary
• Standard transport models can not describe radial flow
• Inclusion of high mass resonances leads to additional flow
• Assumption of an early QGP phase might create additional flow
Marcus Bleicher, CCAST- Workshop 2004
Part II: Probing the late stage of the reaction: Resonances
• Is there a (long living) hadronic rescattering stage at SPS and RHIC?
• Lifetime of the hadronic stage is measured by resonance absorption/re-feeding
• Use different resonances to explore this stage: e.g. mesons: baryons:
• Are resonances dissolved in matter?
,,),892( 0* fK
)1385(),1520(),1232(
Marcus Bleicher, CCAST- Workshop 2004
Hadronic vs leptonic channel
ρ0
ρ0
+
+
-
-
π- π+
ρ0
-
+
ρ0 ρ0π-
π+
π+
π-
Hot and dense medium
Au+Au
Particle yields
Particle spectra
time
pK
pK
Marcus Bleicher, CCAST- Workshop 2004
Statistical model fitting
• Particle ratios well reproduced
• Resonance ratios not reproduced(Braun-Munzinger, QM 2004)
• too low
• K*/K too high
Braun-Munzinger et al.
p/
Marcus Bleicher, CCAST- Workshop 2004
Yields and scaling in AABaryon resonances: Meson resonances:
All ratios a smooth, no sudden resonance disappearance
Marcus Bleicher, CCAST- Workshop 2004
Baryon resonances at RHICAll decaying resonances Finally observed resonances
Signal loss due to rescattering of daughters
Marcus Bleicher, CCAST- Workshop 2004
Meson resonances at RHICAll decaying resonances Finally observed resonances
Note that yields information about all decays (l.h.s), while yields information about r.h.s.
ee
Marcus Bleicher, CCAST- Workshop 2004
What about the centrality dependence?
• Where is the suppression?
• K*/K deceases!
• stays constant!p/
Marcus Bleicher, CCAST- Workshop 2004
Data vs. models Thermal model
[1]:T = 177 MeVB = 29 MeV
[1] P. Braun-Munzinger et.al., PLB 518(2001) 41 D.Magestro, private communication[2] Marcus Bleicher and Jörg Aichelin Phys. Lett. B530 (2002) 81. M. Bleicher and Horst Stöcker .Phys.G30 (2004) 111.
UrQMD [2]
Life time [fm/c] :(1020) = 40 (1520) = 13 K(892) = 4 ++ = 1.7
Rescattering and refeeding are needed rather long living hadron stage
Marcus Bleicher, CCAST- Workshop 2004
How can we understand these differences?
Tch freeze-out
Tkin freeze-out
• Strong decrease in kinetic freeze-out temperature from peripheral to central
• Kinetic freeze-out as low as 80 - 90 MeV
• Consequences for resonance re-feeding
Marcus Bleicher, CCAST- Workshop 2004
Estimate of re-feeding prob.
• can re-created until end of the reaction• re-creation is only possible near chemical freeze-out
Tmms
2
3221
Estimate of available energy for re-feeding at different reaction stages
Marcus Bleicher, CCAST- Workshop 2004
Decay time analysis
• In the model rho mesons are not re-created after T=120 MeV.Check with mass shift.Check hadronic vs leptonicCheck centrality dependence
• Deltas can be re-created until T=80-90 MeV.No centrality dependence
Marcus Bleicher, CCAST- Workshop 2004
Simple mass shift
• Breit-Wiegner distr. for the rho mass
• Fold with thermal distribution
Temperature dependent mass
• For T=150-100 MeV the mass is shifted by 10-20 MeV downwards
Marcus Bleicher, CCAST- Workshop 2004
Rho mass shift predictions
• Mass drops towards central reactions
• Mass drops towards low pt
Marcus Bleicher, CCAST- Workshop 2004
Summary
• K/ shows a peak around 20 GeV:-Peak can not be reproduced by transport models-Maybe sign of tri-critical point
• Observed transverse flow is large:-Strength of flow can not be described in standard transport models-May be sign of early QGP formation-Maybe sign of high mass resonances
• Resonances have been observed-Apparently no resonance dissolution-Statistical models fail to describe data-Strong re-feeding and absorption effects