Update from Kaos

1. Update from Kaos Florian Uhlig Strangeness at SIS Energies

2. 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 Florian Uhlig Strangeness at SIS Energies

3. 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) Florian Uhlig Strangeness at SIS Energies

4. 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 Florian Uhlig Strangeness at SIS Energies

5. Midrapidity Distribution • Select point which are inside cm=90°±10° Florian Uhlig Strangeness at SIS Energies

6. Inclusive Invariant Cross Sectionat Midrapidity Florian Uhlig Strangeness at SIS Energies

7. 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 Florian Uhlig Strangeness at SIS Energies

8. 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- Florian Uhlig Strangeness at SIS Energies

9. 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 Florian Uhlig Strangeness at SIS Energies

10. Equation of State • 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 Florian Uhlig Strangeness at SIS Energies

11. Centrality Dependence 1.5 AGeV, 40° • Group data in 5 centrality bins defined by multiplicity in LAH • Apart calculated using a Glauber calculation • M=/(fr) with fr beeing the fraction of the total reaction cross section in the bin • M ~Apart Florian Uhlig Strangeness at SIS Energies

12. K-/K+-Ratio • Constant K+/K- ratio • K+ produced together with Y to conserve strangeness • K- produced via strangeness-exchange reaction YK-N • Production mechanism of K+ and K- coupled by strangeness-exchange reaction Florian Uhlig Strangeness at SIS Energies

13. Polar Anisotropy • No effect of KN-potentials seen • Polar anisotropy caused by rescattering ? • Different emission times ? Florian Uhlig Strangeness at SIS Energies

14. Azimuthal Particle Emission Side-flow Elliptic flow Florian Uhlig Strangeness at SIS Energies

15. Azimuthal Particle Emission Side-flow v1 < 0 Elliptic flow +/- 180deg dN/df 1 + 2v1cos(f) + 2v2cos(2f) Florian Uhlig Strangeness at SIS Energies

16. Azimuthal Particle Emission Side-flow v2 < 0 mid-rapidity Elliptic flow +/- 90deg dN/df 1 + 2v1cos(f) + 2v2cos(2f) Florian Uhlig Strangeness at SIS Energies

17. Collective Flow at Target Rapidity Ni+Ni 1.93 AGeV • 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 Florian Uhlig Strangeness at SIS Energies

18. Collective Flow of Kaons Ni+Ni 1.93 AGeV Ni+Ni 1.93 AGeV • Similar behavior for kaons, but K >>  • K+N-potential FOPI Daten: P. Crochet et al., Phys. Lett. B 486, 2000 RBUU: W. Cassing and E. Bratkoskaya, Phys. Rep. 308, 1999 Florian Uhlig Strangeness at SIS Energies

19. Passing Time Ni+Ni 1.93 AGeV Midrapidity  • Decreasing v2 with increasing Ebeam • Scattering/Absorbtion of pions in spectator matter • Compare different collision systems • Passing time tp=2R/c Florian Uhlig Strangeness at SIS Energies

20. K+ around Midrapidity KN potential repulsive for K+ • Transport calculations: • with potential • w/o potential 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 Data: Y. Shin et al., Phys. Rev. Lett. 81 (1998) 1576 Florian Uhlig Strangeness at SIS Energies

21. K- around Midrapidity Semi-central 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- ??? Florian Uhlig Strangeness at SIS Energies

22. pt dependence of v2 Florian Uhlig Strangeness at SIS Energies

23. pt dependence of v2 Florian Uhlig Strangeness at SIS Energies

24. pt dependence of v2transport models A. Mishra et al., Phys. Rev. C 70 (2004) 044904 W. Cassing et al., Nucl. Phys.  A 727 (2003) 59-94 C. Hartnack Florian Uhlig Strangeness at SIS Energies

25. 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 ? Florian Uhlig Strangeness at SIS Energies

26. Equation of State Florian Uhlig Strangeness at SIS Energies

27. Passing time Florian Uhlig Strangeness at SIS Energies