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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. Observables. Temperature. Strangeness Resonances. Femtoscopy Fluctuations. Kinetic Freeze-Out.

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International School on:Quark-Gluon Plasma and Heavy Ion Collisions:Past, Present, FutureVilla Gualino, Turino, ItalySoft Probes II

Christoph Blume

University of Heidelberg







Kinetic Freeze-Out

Chemical Freeze-Out


Jets +

Heavy Flavor


strangeness in heavy ion physics
Strangeness in Heavy Ion Physics

Strangeness enhancement as a QGP signature

J. Rafelski and B. Müller, PRL48, 1066 (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)

statistical models
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, 024905 (2004)

hadronic transport models

Pb+Pb@ √sNN = 17.3 GeV


Hadronic Transport Models

Microscopic approach

Hadronic degrees of freedom


Production mechanisms:

Measured and parameterized

cross sections

String-excitation and fragmentation

Medium effects,

Multi-meson fusion,

Mass shifts,









major strangeness carriers kaons and lambdas

Strangeness Conservation




Isospin Symmetry

Isospin Symmetry

K+ (us)

K- (us)

K0 (ds)

 (uds)

K0 (ds)

Major Strangeness Carriers: Kaons and Lambdas



 (uds)

If baryon density is high

weak decay topologies
Weak Decay Topologies

V0 Topology (K0s, Λ):

Ξ- (Cascade) Ω- Topology:

strangeness production in a pion proton event







Strangeness Production in a Pion-Proton Event

Associated production:

strangeness enhancement sps
Strangeness Enhancement (SPS)

NA57: JPG32, 427 (2006)

strangeness enhancement rhic
Strangeness Enhancement (RHIC)

STAR: PRC77, 044908 (2008)

enhancement towards lower energies
Enhancement Towards Lower Energies

√sNN (GeV)

Contrary to naive expectation

Same behavior for multi-strange particles?

particle ratios in p p rhic and lhc
Particle Ratios in p+p: RHIC and LHC

Increase of relative strangeness production in p+p with √s

ALICE: arXiv:1012.3257

at threshold energies
Ξ at Threshold Energies

Expectation for

statistical model

(Andronic et al.)

HADES: PRL103, 132301 (2009)

strangeness enhancement as qgp signature
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)

energy dependence of k ratios
Energy Dependence of K/π Ratios

Quite sharp maximum in K+/π+ ratio

Indication for phase transition (?)

PRC77, 024903 (2008)


energy dependence of hyperon ratios



Energy Dependence of Hyperon/π Ratios

|y| < 0.4



 = 1.5 (+ + -)

|y| < 0.5

PRC78, 034918 (2008)

rapidity distributions
Rapidity Distributions ...

BRAHMS: Au+Au, √sNN = 200 GeV

Landau ...

p+p Data

Pion production ~ Entropy

Isentropic expansion

Description of the pion gas as a 3D relativistic fluid


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

landau works also for heavy ions
Landau ... works also for Heavy Ions

BRAHMS: PRL94, 162301 (2005)

width of the rapidity distribution
Width of the Φ Rapidity Distribution

Expectation for kaon coalescence

K+ + K- → Φ

PRC78, 044907 (2008)

radial expansion and transverse momentum spectra
Radial Expansion and Transverse Momentum Spectra

1/mT dN/dmT

1/mT dN/dmT



No radial flow:

exponential spectrum

(p+p collisions)

With radial flow:

add. boost by expansion (vT)

⇒ blue shifted spectrum

blast wave analysis of particle spectra
Blast Wave Analysis of Particle Spectra



158A GeV

E. Schnedermann and U. Heinz,

PRC50, 1675 (1994)

energy dependence of m t
Energy Dependence of 〈mT〉

NA49: PRC77, 024903 (2008)

radial expansion of strange particles
Radial Expansion of Strange Particles

What about heavy particles (Ξ, Ω, J/ψ) ?

NA57: JPG32, 2065 (2006)

radial expansion of strange particles1
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.

radial expansion of strange particles2
Radial Expansion of Strange Particles

Multi-strange particles sensitive to the partonic flow contribution (?)

STAR: PRL92, 182301 (2004)


Strong decays ⇒ short lifetimes that can be in the

order of the fireball lifetime


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


Rescattering of decay products

⇒ Provide information on the time span between

chemical and kinetic freeze-out

recombination and rescattering of resonances
Recombination and Rescattering of Resonances

Picture adapted

from C. Markert

and P. Fachini

Hot and dense


Particle yields







Particle spectra




rescattering after chemical freeze out
Rescattering after Chemical Freeze-Out

STAR: PRC71, 064902 (2005)

comparison to chemical equilibrium expectation
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.

scaling properties of the meson
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



k and compared to statistical model
K+/π + and Λ/π – Compared to Statistical Model

A. Andronic et al.,

PLB676, 142 (2009)

energy dependence of k ratios1
Energy Dependence of K/π Ratios

Quite sharp maximum in K+/π+ ratio

Indication for phase transition (?)

PRC77, 024903 (2008)

antibaryon baryon ratios
Antibaryon-Baryon Ratios

S = -3

S = -2

S = -1

S = 0

NA49: PRC78, 034918 (2008)

baryon meson ratio k 0 s
Baryon-Meson Ratio: Λ/K0s

Λ/K0s > 1: Cannot be understood in string fragmentation picture

hadronization mechanisms
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

fragmentation vs coalescence

Hadron from


ph = zp, z < 1

Hadron from


ph = p1 + p2

Fragmentation vs Coalescence

Production of baryons favored relative to mesons in

coalescence picture