Helmut Oeschler

Darmstadt University of Technology

Transition from Baryonic to Mesonic Freeze Out

SQM2006, March 28th, 2006

1. Experimental observation of maximal strangeness content around 30 A GeV

comparison with Statistical model

NPA 697(2002) 902

2. Freeze-out condition changes Phys. Lett. B615 (2005)

3. Possible deviation from usual freeze out around 30 A GeV?

4. Strangeness content of a ``corresponding´´

QGP

Chemical Freeze Out

J. Cleymans and K. Redlich, PRL 81 (1998) 5284

Baryons

Stat. Mod. : All exhibit maxima, but at different locations

Mesons

Stat. Mod. : Only K+/π + exhibits a maximum!

Maximum Strangeness around 30 AGeV

P. Braun-Munzinger, J. Cleymans, HO, K. Redlich, NPA 697(2002) 902

λS = 2 sŝ/(uū+ dđ)

Transition from baryonic to mesonic freeze out

entropy prop to T3

J. Cleymans, H.O., K. Redlich, S. Wheaton, Phys. Lett. B615 (2005)

Meson dominated

Baryon dominated

Transition

At this transistion the freeze out condition is changing!

Deviations from the simple unique freeze out possible?

S.Wheaton,

S. Wheaton et al., to appear

Freeze-Out Volume from HBTD. Adamova et al., CERES, PRL 90 (2003)

√√

K-/K+ Ratio from SIS up to RHIC

T(K-) < T(K+) at 1 – 2 A GeV

10-3

1

103

0 0.25 0.5

x101

x102

x103

x105

K+

Au+Au, 1.5AGeV

Ec.m.-m0c2 [GeV]

10x 2

10x 3

10x 4

10x 6

K-

θlab=40o±4o

0 0.25 0.5

A.Förster, KaoS Collab., PRL 91 (2003) 152301

K+

K-

Strangeness Content

A. Schmah et al., TU Darmstadt

Hadron gas Ideal gas of quarks

NPA 697(2002) 902

Why do we observe the strangeness

content of a Hadron Gas and not of a

Quark Gluon Plasma?

R.V. Gavai and S. Gupta, PRD 65 (2002) 094515

λs ~ χS / χu

• Observation qualitatively agree with Stat. Model. But deviations are seen!

• Different location of maxima as a test?

• Early freeze out of K+? Would increase its yield!

• Equilibrated quark gas would give a very high yield of strangeness!

Thank you!

Thank you!

Expected Centrality Dependence (SM)

Pion density

n(π) = exp(-Eπ/T)

Strangeness is conserved!

Kaon density

NN N Λ K+

n(K) = exp(-EK/T)

[g V ∫ … exp[-(EΛ-µB)/T]

J. Cleymans, HO, K. Redlich,

PRC 60 (1999)

Qualitative agreement! Except for AGS!

AGS

Au+Au 6 A GeV

P. Chung et al.,

E895 Coll.

PRL 91(2003)

Updated

M ~ (Apart ) α

All these observation agree with a hadron gas at chemical equilibrium

What did we learn?

Many arguments that „QGP“ has been formed.

1.What dynamics causes freeze out?

2. Where do we observe quark degrees?

Strangeness Enhancement

Data: WA97 New: NA57 Theory: S. Hamieh, K. Redlich A. Tounsi, PL B486 (2000) 61

Strangeness enhancement as a signal of QGP?

Canonical strangeness suppression?

λS = 2 sŝ/(uū+ dđ)

SIS: nuclear EoS, K+ and K-: Different freeze out

K- via strangeness exchange

SIS and AGS: Strangeness exchange important

Ξ at 6 AGeV yield in agreement with Stat. Mod.

Max. strangeness content around 30 AGeV

Transition from Baryonic to Mesonic Freeze Out

RHIC: Statistical model works very well

LHC:?

SIS: nuclear EoS, K+ and K-: Different freeze out

A. Förster et al.,(KaoS Coll.) PRL 91 (2003)

SIS and AGS: Strangeness exchange important

J. Cleymans et al., PLB 603 (2004)

Transition from Baryonic to Mesonic Freeze Out

J. Cleymans et al., Phys. Lett. B 615 (2005)

RHIC: Statistical model works very well

And beyond!

At LHC particle production will be dominated by hard processes!

Jets!

Will this destroy the simple picture (SM)?

More strangeness due to faster decay from the QGP?

Less strangeness due to fragmentation?

Will one observe a hadronic composition in jets as expected from the two parameters T and μB ?

Interesting already in pp collisions

… v2, jet quenching, heavy flavor,…

P. Braun-Munzinger, J. Cleymans, HO, K. Redlich, NPA 697(2002) 902

Do the slopes make a consistent picture?

Ni+Ni 1.93 AGeV

F. Uhlig, TU DA Diss.

Protons, K+ and pions

cross

K- differ!

T(stat. Model) = 74 MeV

PRC 59 (1999)

Transition

√

A. Mischke, Ph.D. thesis

Statistical Model

P. Braun-Munzinger, D. Magestro, K. Redlich, J. Stachel, PL B518 (2001) updated

Statistical Model

Statistical Model for SIS

J. Cleymans, H. O., K. Redlich, PRC 59 (1999)

Ebeam[AGeV]

K+

K-

0

100

200

05 10 15 20

Dynamics of K+ and K-

K+ yield established early by the high-density phase, not changed due to s-conservation (K+ from the interior)

K+ slopes (and angular distributions) dominated by rescattering

K- yield established late by Λ and π concentration (K- from the surface)

Even if K- from a thermal source of Λ and π, T(K-) is smaller than T(source). Only those K- are observed which did NOT had an interaction

Stat. Model describes the ratios, but does not describe T(K- ).

K- and K+ are linked

Au+Au and Ni+Ni 1.5 AGeV

A. Förster, F. Uhlig et al., KaoS PRL 91 (2003) 152301

dashed line: stat. Model

K- and K+ are linked via strangeness exchange

Λ π -> K- N

„Law of mass action“

J. Cleymans, et al. PLB603(2004)

Maximum around 30 A GeV