Strangeness Dynamics and Transverse Pressure in HIC

1
Strangeness Dynamics andTransverse Pressure in
HIC

• Marcus Bleicher
• Institut für Theoretische Physik
• Goethe Universität Frankfurt
• Germany

2
For further reading

• E. L. Bratkovskaya et al, Strangeness dynamics
  and transverse pressure in relativistic nucleus
  nucleus collisions,'' Phys. Rev. C 69, 054907
  (2004)
• E. L. Bratkovskaya et al. , Strangeness
  dynamics in relativistic nucleus nucleus
  collisions,'' Prog. Part. Nucl. Phys. 53, 225
  (2004)
• M. Bleicher and H. Stocker, Dynamics and
  freeze-out of hadron resonances at RHIC,'' J.
  Phys. G 30, S111 (2004)
• M. Bleicher, Probing hadronization and
  freeze-out with multiple strange hadrons and
  strange resonances,'' Nucl. Phys. A 715, 85
  (2003)
• M. Bleicher and J. Aichelin, Strange resonance
  production Probing chemical and thermal
  freeze-out in relativistic heavy ion
  collisions,'' Phys. Lett. B 530, 81 (2002)

3
Contents

• Chemical equilibrium stage
• The horn, the step
• Kinetic decoupling stage
• Resonance (non-) suppression
• Summary

4
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

5
Part I Evidence for the tri-critical point?

• 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
6
PP Excitation functions

• PP works nicely in both models
• Pythia used for hard scatterings above 50 GeV

7
AA Excitation functions

• 4 and mid-y abundancies OK
• Energy dependence OK
• Hadron-string models work well

8
Excitation functions ratios

• Horn in the ratio not reproduced
• well reproduced
• relative strange baryon
  enhancement reproduced

9
Ratio excitation functions Summary

• Yields are well reproduced
• Most ratios can be understood in transport
  models
• Model K/pi ratios do not reproduce the strong
  peak observed in data

10
Proton-Proton

• PP works well
• pQCD needed at RHIC
• PYTHIA included in
• UrQMD 2.x and HSD

11
Proton-Nucleus

• pA is well under control
• What about AA?

12
Transverse mass spectra

• Standard UrQMD and HSD underestimate the data
• Additional resonances from 2-3 GeV may improve
  the description (UrQMD 2.1)

13
Inverse slope systematics

• Standard transport models fail
• What is missing?
• Maybe high mass resonanceslike in UrQMD 2.1
• Maybe Cronin effect at high
• energies (HSD)
• Maybe initial QGP pressure

14
Hints from elliptic flow

• Data shows saturation of scaled v2
• High mass resonances like in UrQMD 2.1 can not
  explain v2 above 40 AGeV
• Strong hint for initial QGP pressure from
  30 AGeV on !

30 AGeV
Data for h-
15
Phase diagram

• QGP might be reachedalready at low SPS energy
  !
• Tricritical point around 10-40 GeV
• No phase transition at RHIC
• Necessary to explore 10-30 AGeV energy region
  to study the phase transition

16
Flow excitation functions Summary

• Standard transport models can not describe
  radial flow
• Inclusion of high mass resonances leads to
  additional flow (maybe necessary at low
  energies)
• Inclusion of Cronin effect leads to additional
  flow (maybe necessary at high energies)
• Assumption of an early QGP phase might create
  additional flow

17
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?

18
Hadronic vs leptonic channel
AuAu
Hot and dense medium
Particle yields
L
K
K
p
Particle spectra
p
p
L
time
Adapted from C. Markert and P. Fachini
19
Statistical model fitting

• Particle ratios well reproduced
• Resonance ratios not reproduced
  (Braun-Munzinger, QM 2004)
• too low
• K/K too high

Kai Schweda et al., QM 2004
20
Yields and scaling in AA
Baryon resonances
Meson resonances
Yields
Ratios
All ratios a smooth, no sudden resonance
disappearance
21
Baryon resonances at RHIC
All decaying resonances
Finally observed resonances
AuAu, 5
Signal loss due to rescattering of daughters
22
Meson resonances at RHIC
All decaying resonances
Finally observed resonances
AuAu, 5
Note that yields information
about all decays (l.h.s), while
yields information about r.h.s.
23
What about the centrality dependence?

• Where is the suppression?
• K/K deceases!
• stays constant!

AuAu
Calculation by P. Fachini
24
Data vs. models
Thermal model 1 T 177 MeV mB 29 MeV
Life time fm/c ? (1020) 40 L(1520)
13 K(892) 4 ?
1.7 r (770) 1.3
UrQMD 2
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.
Rescattering and refeeding are needed
rather long living hadron stage
From C. Markert
25
How can we understand these differences?
STAR data

• 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

26
Estimate of re-feeding prob.
Estimate of available energy for re-feeding at
different reaction stages

• can re-created until end of the
  reaction
• re-creation is only possible near
  chemical freeze-out

27
Decay time analysis

• In the model rho mesons are not re-created after
  T120 MeV. Check with mass shift.
  Check hadronic vs leptonic Check centrality
  dependence
• Deltas can be re-created until T80-90 MeV.No
  centrality dependence of ratios

28
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- Flow can
  not be described in standard transport models-
  Maybe sign of early QGP formation- Maybe sign
  of high mass resonances (low energies)- Maybe
  Cronin enhancement (high energies)
• Resonances have been observed- Apparently no
  resonance dissolution- Statistical models fail
  to describe data- Strong re-feeding and
  absorption effects

29
Thanks

• Elena Bratkovskaya
• Henning Weber
• Christina Markert
• Patricia Fachini
• Manuel Reiter
• Sascha Vogel
• Xianglei Zhu

We do have a POST-DOC position!