Helmut OeschlerDarmstadt University of Technology

Strangeness Production at 1 -2 AGeV

Erice, September 2008

Results mainly from the KaoS Collaboration

Phys. Rev. C (2007)

Detailed IQMD Calculations

Phys. Rep. in preparation

with C. Hartnack, J. Aichelin

Au+Au

C+C

Creation of Strange Mesons

udu

uu

uds

su

p

K-

K- absorption

udu

udu

n

p

udd

su

K+

su

p

K

ddu

n

uds

n

p

udd s

u

K+

ddu

nudu

uds

n

du

udd

su

K+

Mean free path of Kaons and Antikaons

K+: "nearly" undisturbed messengers

mean free path at ρ0:λ(π) = 0.3 fmλ(K+) = 5 fmλ(K-) = 0.8 fm

K- absorption by strangeness exchange reactions: K- p → Y πo

K+ production below and at threshold

IQMD calculations, Au+Au central collisionsComparision with data

Before getting started: Are the pions okay?

Data: A. Wagner et al., KaoS

N/Z ratio and Coulomb

KaoS Collaboration, PRC 75 (2007)

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

Is s exch. in equil.?

Law-of-mass action

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

K- and K

+ are linked

M ~ Aγ

IQMD C. Hartnack et al., PRL 93 (2004)

Time Evolution of K+ and K- Production

C.Hartnack, H.O., J. Aichelin, PRL 90(2003)

Strangeness exchange dominates! Only 20% of all K- survive!

Kaon Spectra

PRC 75 (2007)

Trend of the K+ slopes

What determines the shape of the K+ spectra?

According to IQMD calculations

Slopes of K- are lower!

Influence on K- spectra

Au+Au: only 20% survive

about 30% of those do not scatter

K+ yield determined at production

K+ spectral shape at last collision

K- yield and spectral shape at last collision

Out-of-plane Emission

Ni+Ni 1.93 AGeV (F .Uhlig, PRL 95 (2005))

IQMD Calculations (C. Hartnack et al.)

F. Uhlig, et al., KaoS, PRL 95 (2005)

Latest from KaoS: v2 as a function of pt Au+Au 1.5 AGeV, M. Ploskon, KaoS to be published!

IQMD calculations, C. Hartnack

T. Gaitanos et al., EPJ A12, 421 (2001)

The nuclear equation of state

Densities reached in Au+Au ≈ 2-3 ρ0, in C+C much less

KaoS Collaboration

C. Sturm et al.,

PRL 86 (2001)

A.Förster et al.,

PR C75 (2007)

RQMD: C. Fuchs et al.,

PRL 86 (2001)

IQMD: C. Hartnack et al.,

PRL 96 (2006)

Results confirmed also with several calculations and other observables!

C. Hartnack, HO, J. Aichelin, PRL 96 (2006)

• K+ yield determined at production which is around twice ρ0

• K+ spectra dominated by scattering, some influence by KN potential

• K- yield dominated by strangeness exchange at densities around ρ0

• K- spectra influenced by absorption, scattering and potential

Best observable for KN Potential?

K+ yield

K- yield

K-/K+ ratio

Difference in slopes

Spectra at low momenta

v2 (K+)

v2 (K-)

*

-

-

-

**

* (*)

* ?

Input ?

Input, K+, pi, …

Same only K+ cancels

K+ rescattering

K- decay

Difficult to measure

Contribution of rescatt.?

Emission time and potential(?)K+(AuAu)/K+(CC) * * * EOS! Most uncertainties

cancel

Grazie!