Investigation of subthreshold K+ and K- production

what remains from the KN potentials?C.Hartnack and J. Aichelin

SUBATECH, Ecole des Mines & CNRS & University, Nantes (France)

Outline: ● The IQMD model and its KN potentials● Comparison to KaoS Data● Slope of K+ and K- spectra● Influence of potentials and rescattering● Influence of channels and production times● Conclusion

The IQMD model

● Semiclassical microscopic model on an event by event basis● Full time-evolution of each event allows for a view inside the reaction● Includes nucleons, deltas , pions with their isospin degrees of freedom● Nuclear eos, Coulomb, asymmetry, Yukawa and momentum dep. pot.● Virtual treatment of strange particles allows for high statistics● KN optical potential

KN optical potential

Parametrisation :RMF calculations of J. Schaffner-Bielich

Attention: K- production process via hyperons may involve

K+ and K- potentials for K- production

K- pot.

K+pot

Comparison to KaoS DATA

● Calculations in good agreement with data by A.Foerster● KN potential penalizes K+ and K- production

Comparison of slopes for K+ and K-

● KaoS claims different slopes of K+ and K- but measures only limited momentum range ● K+ from IQMD show different slopes at low and high p

4π

Influence of potential and rescattering

● No influence of K+ potentials on the slope ● Rescattering influences high energy tail

Influence of potential on K- spectra

● Only K+ potential influences the K- slope: reduced production of hyperons● K- potential effect only at very low energies

Analysis of the production time

K+ are produced in the high density phase while surviving K- stem from later times

Definition of 3 time windows

early t< 8fm/c

mid 8<t<16fm/c

late t> 16fm/c

Time windows for K+

● Strong contribution of early times● Similar time profile for all channels

Time windows for K- spectra

● Slope depends on production time● Different channels show up at different times

Contribution of different channels

● K+ : no strong difference in slopes● K- : Different slopes for π–Y and B-Y

Conclusion

● K+ spectra show different slopes at low and high momenta

● KN-potentials show little effects on slope of K+ ● K- spectra are only slightly influenced by K- potentials

● B-Y and π-Y induced K-reactions:1) Appear at different times2) Show different slopes3) Consequently: the experimental slope allows to get

information on the production channels but not on the KN potentials

● Importance of the reaction dynamics for understanding the slopes of the spectra

Appendix (or stuff that you will only see if you really ask for it)

● K+ spectra, centrality dependence● K- spectra, centrality dependence ● K- spectra, influence of absorption ● cos() K+ to K-, K+ potential and rescattering● cos() K- potential and absorption● cos() K+ time-window, channels, centrality● cos() K- time-window, channels, centrality ● K+ K- azimuthal distributions at midrapidity● K+ K- azimuthal distributions: potential● K+ K- azimuthal distributions: rescattering ● Souvenirs of SQM 2001

Centrality dependence K+ spectra

Centrality dependence K- spectra

Influence of K- absorption

● Suppression of absorption recovers many K- produced in early times ● Influence especially at low momenta

K+ cos() distributions

K- cos() distributions

K+ cos() distributions

K- cos() distributions

K+&K- azimuthal distributions

K+ & K- azimuthal dist.: potential

K+ & K- azimuthal dist.: rescattering

Souvenirs from SQM 2001

Influence of KN potentials