Update from Kaos

17.01.2008 Florian UhligStrangeness at SIS Energies

Update from Kaos


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


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)


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)


Midrapidity Distribution

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


Inclusive Invariant Cross Sectionat Midrapidity


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


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-


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


• 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


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°


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


Polar Anisotropy

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


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))



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


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


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


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


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


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


pt dependence of v2


pt dependence of v2


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


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 ?


Equation of State


Passing time

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Update from Kaos