Update from Kaos

17.01.2008 Florian UhligStrangeness at SIS Energies

Update from Kaos

17.01.2008 Florian UhligStrangeness at SIS Energies

Outline

• Kaon Production– Inclusive results

• Slopes• Polar anisotropy• Multiplicities• Equation of State

– Centrality dependence• K-/K+-Ratio• Polar anisotropy

• Azimuthal Particle Emission

Data: A. Förster et. al, Phys. Rev. C75 (2007) 024906

17.01.2008 Florian UhligStrangeness at SIS Energies

Setup

• Selective Kaon trigger (ToF, Cherenkov)

• Background reduction (3MWPCs, double ToF measurements)

• Reaction plane reconstruction (Small-Angle Hodoscope) and event characterization – centrality (Large-Angle Hodoscope)

17.01.2008 Florian UhligStrangeness at SIS Energies

Inclusive Production Cross Section

• Inclusive = no centrality selection

• Extract slopes and total production cross scection with one consistent method

• Lines are result of simultaneous fit

€

Ed3σ

dp3=C 1+ a2 cos

2(θcm )[ ]Ecm exp(−EcmT)

17.01.2008 Florian UhligStrangeness at SIS Energies

Midrapidity Distribution

• Select point which are inside cm=90°±10°

17.01.2008 Florian UhligStrangeness at SIS Energies

Inclusive Invariant Cross Sectionat Midrapidity

17.01.2008 Florian UhligStrangeness at SIS Energies

Slopes

• Fit midrapidity spectra with Maxwell-Boltzmann function

• Slopes are increasing with increasing beam energy

• K+ slope higher than K- slope at same beam energy

• At same centrality K+ slope higher than K- slope

17.01.2008 Florian UhligStrangeness at SIS Energies

Polar Anisotropy

• Energy dependence is determined at midrapidity

• Normalize data points inv(Ecm, cm) to inv(Ecm, cm=90°)

• Forward-backward preference

• More pronounced for K+ than K-

• Different freeze-out conditions (times and/or potentials) for K+ and K-

17.01.2008 Florian UhligStrangeness at SIS Energies

Multiplicities

• Results of simultaneous fits are used to extrapolate to phase-space regions not measured

• Calculate total reaction cross section using Glauber calculations

• Strong rise due to the proximity of thresholds in binary NN collisions

17.01.2008 Florian UhligStrangeness at SIS Energies

• K+ produced in multi step collisions• Baryonic density reached in Au+Au

reactions is 2-3 0 and depends on compression modulus of nuclear matter KN, weak dependence and lower density in C+C collisions

• (M/A)AU/(M/A)C is sensitiv to KN

• Experimental uncertainties partly cancel

• Ratio hardly affected by less known input to transport model calculations

• Models favour soft EoS

Equation of State

17.01.2008 Florian UhligStrangeness at SIS Energies

Centrality Dependence

• Group data in 5 centrality bins defined by multiplicity in LAH

• Apart calculated using a Glauber calculation

• M=/(fr) with fr beeing the fraction of the total reaction cross section in the bin

• M ~Apart

1.5 AGeV, 40°

17.01.2008 Florian UhligStrangeness at SIS Energies

K-/K+-Ratio

• Constant K+/K- ratio• K+ produced together with Y to

conserve strangeness• K- produced via strangeness-

exchange reaction YK-N• Production mechanism of K+

and K- coupled by strangeness-exchange reaction

17.01.2008 Florian UhligStrangeness at SIS Energies

Polar Anisotropy

• No effect of KN-potentials seen• Polar anisotropy caused by rescattering ?• Different emission times ?

17.01.2008 Florian UhligStrangeness at SIS Energies

Azimuthal Particle Emission

17.01.2008 Florian UhligStrangeness at SIS Energies

Azimuthal Particle Emission

-180 -90 0 90 180

0

0.2

[Deg]φ

p < 0.15n 0.05 < y

-180 -90 0 90 180

0

0.2

[Deg]φ

p < 0.15n 0.05 < y

0.01± = -0.27 1v

0.01± = -0.02 2v

v1 < 0

+/- 180deg

dN/ddN/d 1 + 21 + 2vv11cos(cos() + 2) + 2vv22cos(2cos(2))

17.01.2008 Florian UhligStrangeness at SIS Energies

Azimuthal Particle Emission

dN/ddN/d 1 + 21 + 2vv11cos(cos() + 2) + 2vv22cos(2cos(2))

-180 -90 0 90 1800

0.1

[Deg]φ

+

-180 -90 0 90 1800

0.1

[Deg]φ

+

0.01± = 0.03 1v

0.01± = -0.13 2v+/- 90deg

v2 < 0mid-rapiditymid-rapidity

17.01.2008 Florian UhligStrangeness at SIS Energies

Collective Flow at Target Rapidity

•Protons show expected flow•Nice agreement between KaoS and FOPI

•shadowing of pions - short mean

•Emission time depends on energy

FOPI Data: A. Andronic et al. Phys. Rev., C64:041604, 2001.

KaoS Data: M. Ploskon, PhD Thesis, University Frankfurt, 2005 F.Uhlig, PhD Thesis, TU Darmstadt, 2003

Ni+Ni 1.93 AGeV

17.01.2008 Florian UhligStrangeness at SIS Energies

Collective Flow of Kaons

• Similar behavior for kaons, but K >>

• K+N-potential

FOPI Daten: P. Crochet et al., Phys. Lett. B 486, 2000RBUU: W. Cassing and E. Bratkoskaya,Phys. Rep. 308, 1999

Ni+Ni 1.93 AGeVNi+Ni 1.93 AGeV

17.01.2008 Florian UhligStrangeness at SIS Energies

Passing Time

• Decreasing v2 with increasing Ebeam• Scattering/Absorbtion of pions in spectator matter

• Compare different collision systems• Passing time tp=2R/c

Ni+Ni 1.93 AGeV Midrapidity

17.01.2008 Florian UhligStrangeness at SIS Energies

K+ around Midrapidity

Data: Y. Shin et al., Phys. Rev. Lett. 81 (1998) 1576

RBUU Stony Brook:G.Q.Li et al., Phys. Lett. B 381 (1996)

QMD Tübingen: Z.S. Wang et al., Eur. Phys. J. A5 (1999) 275

KN potential repulsive for K+

Transport calculations:• with potential• w/o potential

17.01.2008 Florian UhligStrangeness at SIS Energies

K- around Midrapidity

Data: Ni+Ni 1.93 AGeV[F.Uhlig, A. Förster et al.,Phys.Rev.Lett. 95 (2005) 012301

IQMD: Ch. Hartnack

In-Plane flow of K- ???

Semi-central

17.01.2008 Florian UhligStrangeness at SIS Energies

pt dependence of v2

17.01.2008 Florian UhligStrangeness at SIS Energies

pt dependence of v2

17.01.2008 Florian UhligStrangeness at SIS Energies

pt dependence of v2 transport models

A. Mishra et al.,Phys. Rev. C 70 (2004) 044904 W. Cassing et al., Nucl. Phys.  A 727 (2003) 59-94

C. Hartnack

17.01.2008 Florian UhligStrangeness at SIS Energies

Summary• K+ excitation function measured with heavy-ion collisions

favours rather soft EoS• Different freeze-out conditions for K+ and K-

• K+/K- ratio as a function of Apart -> strangeness-exchange – the dominant production channel for K-

• Pion clock – high energetic pions emitted early• Elliptic flow of K+ mesons – evidence for repulsive K+N

potential or rescattering ?• Elliptic flow of K- - an evidence for attractive K-N potential or

rather high sensitivity to emission time ?

17.01.2008 Florian UhligStrangeness at SIS Energies

Equation of State

17.01.2008 Florian UhligStrangeness at SIS Energies

Passing time