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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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Christoph Blume University of Heidelberg

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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


Observables

Temperature

Strangeness

Resonances

Femtoscopy

Fluctuations

Kinetic Freeze-Out

Chemical Freeze-Out

Flow

Jets +

Heavy Flavor

Photons


Strangeness


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

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)


Pb+Pb@ √sNN = 17.3 GeV

UrQMD

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,

...

Examples:

UrQMD

HSD

NEXUS

(AMPT)

(EPOS)

...


Strange Particles


Strangeness Conservation

s

s

=

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


Measurement of Charged Kaons via dE/dx

Bethe-Bloch function:


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


Weak Decay Topologies

V0 Topology (K0s, Λ):

Ξ- (Cascade) Ω- Topology:


p

+

-

-

K0

-

Strangeness Production in a Pion-Proton Event

Associated production:


Strangeness Production in a Heavy Ion Event


Reconstruction via Decay Topology

NA49

NA57

NA57


Armenteros-Podolanski Plot


Strangeness Enhancement (SPS)

NA57: JPG32, 427 (2006)


Strangeness Enhancement (RHIC)

STAR: PRC77, 044908 (2008)


Enhancement Towards Lower Energies

√sNN (GeV)

Contrary to naive expectation

Same behavior for multi-strange particles?


Particle Ratios in p+p: RHIC and LHC

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

ALICE: arXiv:1012.3257


Ξ at Threshold Energies

Expectation for

statistical model

(Andronic et al.)

HADES: PRL103, 132301 (2009)


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/π Ratios

Quite sharp maximum in K+/π+ ratio

Indication for phase transition (?)

PRC77, 024903 (2008)

arXiv:1007.2613


/

+/

Energy Dependence of Hyperon/π Ratios

|y| < 0.4

/

-/

 = 1.5 (+ + -)

|y| < 0.5

PRC78, 034918 (2008)


Maximum of Relative Strangeness Production


Chemical Freeze-Out Curve


Chemical Freeze-Out in the QCD Phase Diagram


Spectra


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

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


Landau ... works also for Heavy Ions

BRAHMS: PRL94, 162301 (2005)


Width of the Φ Rapidity Distribution

Expectation for kaon coalescence

K+ + K- → Φ

PRC78, 044907 (2008)


Radial Expansion and Transverse Momentum Spectra

1/mT dN/dmT

1/mT dN/dmT

mT

mT

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

Central

Pb+Pb

158A GeV

E. Schnedermann and U. Heinz,

PRC50, 1675 (1994)


Energy Dependence of Kinetic Freeze-Out

arXiv:1007.2613


Energy Dependence of 〈mT〉

NA49: PRC77, 024903 (2008)


Radial Expansion of Strange Particles

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

NA57: JPG32, 2065 (2006)


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 Particles

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

STAR: PRL92, 182301 (2004)


Resonances


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


Recombination and Rescattering of Resonances

Picture adapted

from C. Markert

and P. Fachini

Hot and dense

medium

Particle yields

K*

K

π

π

K

K

Particle spectra

π

K*

Time


Measurement of Resonances: Σ(1385) and Λ(1520)

STAR: PRC71, 064902 (2005)


Rescattering after Chemical Freeze-Out

STAR: PRC71, 064902 (2005)


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 Φ Meson

No scaling with K+ × K-

(coalescence picture)

Scaling with (s-Quarks)2

Φ = ss

K+ ∝ s-Quarks

K- + Λ ∝ s-Quarks

_

_


K+/π + and Λ/π – Compared to Statistical Model

A. Andronic et al.,

PLB676, 142 (2009)


Energy Dependence of K/π Ratios

Quite sharp maximum in K+/π+ ratio

Indication for phase transition (?)

PRC77, 024903 (2008)


Antibaryon-Baryon Ratios

S = -3

S = -2

S = -1

S = 0

NA49: PRC78, 034918 (2008)


Baryon-Meson-Ratios


Baryon-Meson Ratio: Λ/K0s

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


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


Hadron from

fragmentation:

ph = zp, z < 1

Hadron from

coalescence:

ph = p1 + p2

Fragmentation vs Coalescence

Production of baryons favored relative to mesons in

coalescence picture


_

Baryon-Meson Ratio: Ω(sss)/Φ(ss)


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