1. Christoph Blume University of Heidelberg
International School on: Quark-Gluon Plasma and Heavy Ion Collisions: Past, Present, Future Villa Gualino, Turino, Italy Soft Probes II
Christoph Blume
University of Heidelberg

2. Observables Temperature Strangeness Resonances Femtoscopy Fluctuations
Chemical Freeze-Out
Kinetic Freeze-Out
Temperature
Femtoscopy
Fluctuations
Flow
Jets +
Heavy Flavor
Photons
Strangeness
Resonances

3. Strangeness

4. Strangeness in Heavy Ion Physics
Strangeness enhancement as a QGP signature
J. Rafelski and B. Müller, PRL48, (1982)
P. Koch, B. Müller, and J. Rafelski, Phys. Rep. 142, 167 (1986)
Strangeness has to be produced (no s-Quarks in nucleons)
Thresholds are high in hadronic reactions,
e.g..: N + N  N + K+ +  (Ethres  700 MeV)
Fast equilibration in a QGP via partonic processes,
e.g. gluon-fusion
⇒ Enhancement of strange particle production in A+A relative
to p+p expected (in particular multi-strange particles)

5. Statistical Models Multiplicities determined by statistical weights
(⇒ chemical equilibrium)
Grand-canonical partition function:
⇒ Parameters: V, T, μB, γS
Details: see F. Becattini’s lecture
A.Andronic et al.
PLB673, 142 (2009)
F.Becattini et al.,
PRC69, (2004)

6. Hadronic Transport Models
Microscopic approach
Hadronic degrees of freedom
Non-equilibrium
Production mechanisms:
Measured and parameterized
cross sections
String-excitation and fragmentation
Medium effects,
Multi-meson fusion,
Mass shifts,
...
√sNN = 17.3 GeV
UrQMD
Examples:
UrQMD
HSD
NEXUS
(AMPT)
(EPOS)
...

7. Strange Particles

8. Major Strangeness Carriers: Kaons and Lambdas
Strangeness Conservation  =
Isospin Symmetry
K0 (ds)
K+ (us) 
K- (us)
 (uds)
>> 
If baryon density is high

9. Measurement of Charged Kaons via dE/dx
Bethe-Bloch function:

10. Combination of dE/dx and Time-Of-Flight (TOF)

11. Weak Decay Topologies
V0 Topology (K0s, Λ):
Ξ- (Cascade) Ω- Topology:

12. Strangeness Production in a Pion-Proton Event-  K0 p +
Associated production:

13. Strangeness Production in a Heavy Ion Event

14. Reconstruction via Decay Topology
NA49
NA57
NA57

15. Armenteros-Podolanski Plot

16. Strangeness Enhancement (SPS)
NA57: JPG32, 427 (2006)

17. Strangeness Enhancement (RHIC)
STAR: PRC77, (2008)

18. Enhancement Towards Lower Energies
√sNN (GeV)
Contrary to naive expectation
Same behavior for multi-strange particles?

19. Particle Ratios in p+p: RHIC and LHC
Increase of relative strangeness production in p+p with √s
ALICE: arXiv:

20. Ξ at Threshold Energies
Expectation for
statistical model
(Andronic et al.)
HADES: PRL103, (2009)

21. Strangeness Enhancement as QGP Signature ?
Is it a dominantly partonic effect or can hadronic processes lead to the same fast equilibration?
Multi-meson fusion processes
C. Greiner and S. Leupold, J. Phys. G 27, L95 (2001)
Dynamic equilibration at the phase boundary?
P. Braun-Munzinger, J. Stachel, and C. Wetterich, Phys. Lett. B 596, 61 (2004)
Hadronization generally a statistical phenomenon?
U. Heinz, Nucl. Phys. A 638, 357c (1998), R. Stock, Phys. Lett. B 456, 277 (1999)

22. Energy Dependence of K/π Ratios
Quite sharp maximum in K+/π+ ratio
Indication for phase transition (?)
PRC77, (2008)
arXiv:

23. Energy Dependence of Hyperon/π Ratios
/ −
-/
+/
 = 1.5 (+ + -)
PRC78, (2008)

24. Maximum of Relative Strangeness Production

25. Chemical Freeze-Out Curve

26. Chemical Freeze-Out in the QCD Phase Diagram

27. Spectra

28. Rapidity Distributions ...
BRAHMS: Au+Au, √sNN = 200 GeV

29. Landau ... p+p Data Prediction: dN/dy is Gaussian of a width given by:
Pion production ~ Entropy
Isentropic expansion
Description of the pion gas as a 3D relativistic fluid
Prediction:
dN/dy is Gaussian of a width given by:
L. D. Landau, Izv. Akad. Nauk. SSSR 17 (1953) 52
P. Carruthers and M. Duong-Van, PRD8 (1973) 859

30. Landau ... works also for Heavy Ions
BRAHMS: PRL94, (2005)

31. Width of the Φ Rapidity Distribution
Expectation for kaon coalescence
K+ + K- → Φ
PRC78, (2008)

32. Radial Expansion and Transverse Momentum SpectramT
1/mT dN/dmT mT
1/mT dN/dmT
No radial flow:
exponential spectrum
(p+p collisions)
With radial flow:
add. boost by expansion (vT)
⇒ blue shifted spectrum

33. Blast Wave Analysis of Particle Spectra
Central
Pb+Pb
158A GeV
E. Schnedermann and U. Heinz,
PRC50, 1675 (1994)

34. Energy Dependence of Kinetic Freeze-Out
arXiv:

35. Energy Dependence of 〈mT〉
NA49: PRC77, (2008)

36. Radial Expansion of Strange Particles
What about heavy particles (Ξ, Ω, J/ψ) ?
NA57: JPG32, 2065 (2006)

37. Radial Expansion of Strange Particles
Particles with low hadronic cross sections: Ξ, Ω, J/ψ
⇒ Not sensitive to flow in hadronic, but maybe to partonic phase
N. Xu and M. Kaneta, NPA698, 306 (2002) 306.

38. Radial Expansion of Strange Particles
Multi-strange particles sensitive to the partonic flow contribution (?)
STAR: PRL92, (2004)

39. Resonances

40. Resonances Strong decays ⇒ short lifetimes that can be in the
order of the fireball lifetime
Examples:
K(892) → K+ + π - : cτ = 3.91 fm
Φ(1020) → K+ + K- : cτ = 46.5 fm
Σ-(1385) → Λ + π - : cτ = 5.08 fm
Λ(1520) → p + K- : cτ = 12.7 fm
Should be sensitive to the late phase of the hadronic fireball
Regeneration
Rescattering of decay products
⇒ Provide information on the time span between
chemical and kinetic freeze-out

41. Recombination and Rescattering of Resonances
Hot and dense
medium
Particle yields
Particle spectra
Time K* π K
Picture adapted
from C. Markert
and P. Fachini

42. Measurement of Resonances: Σ(1385) and Λ(1520)
STAR: PRC71, (2005)

43. Rescattering after Chemical Freeze-Out
STAR: PRC71, (2005)

44. Comparison to Chemical Equilibrium Expectation
Pb+Pb, √sNN = 17.3 GeV
Pb+Pb, √sNN = 17.3 GeV
NA49: pub. in preparation
HGM: F. Becattini et al.

46. Scaling Properties of the Φ Meson
No scaling with K+ × K-
(coalescence picture)
Scaling with (s-Quarks)2
Φ = ss
K ∝ s-Quarks
K- + Λ ∝ s-Quarks _

47. K+/π + and Λ/π – Compared to Statistical Model
A. Andronic et al.,
PLB676, 142 (2009)

48. Energy Dependence of K/π Ratios
Quite sharp maximum in K+/π+ ratio
Indication for phase transition (?)
PRC77, (2008)

49. Antibaryon-Baryon Ratios
NA49: PRC78, (2008)

50. Baryon-Meson-Ratios

51. Baryon-Meson Ratio: Λ/K0s
Λ/K0s > 1: Cannot be understood in string fragmentation picture

52. Hadronization Mechanisms
Fragmentation (Lund model)
String fragments via qq creation
Original parton momentum is
divided among resulting partons _
Quark coalescence
Hadrons form by combining quarks
from quark soup (QGP)
Would be dominating at intermediate pt

53. Fragmentation vs Coalescence
Hadron from
fragmentation:
ph = z p, z < 1
coalescence:
ph = p1 + p2
Production of baryons favored relative to mesons in
coalescence picture

54. Baryon-Meson Ratio: Ω(sss)/Φ(ss)_
Baryon-Meson Ratio: Ω(sss)/Φ(ss)