1,010,209 research outputs found
Strangeness Balance in HADES Experiments and the Xi- Enhancement
HADES data on a strangeness production in Ar+KCl collisions at 1.76A GeV are
analyzed within a minimal statistical model. The total negative strangeness
content is fixed by the observed K^+ multiplicities on event-by-event basis.
Particles with negative strangeness are assumed to remain in chemical
equilibrium with themselves and in thermal equilibrium with the environment
until a common freeze-out. Exact strangeness conservation in each collision
event is explicitly preserved. This implies that Xi baryons can be released
only in events where two or more kaons are produced. An increase of the
fireball volume due to application of a centrality trigger in HADES experiments
is taken into account. We find that experimental ratios of K-/K+, Lambda/K+ and
Sigma/K+ can be satisfactorily described provided in-medium potentials are
taken into account. However, the calculated Xi-/Lambda/K+ ratio proves to be
significantly smaller compared to the measured value (8 times lower than the
experimental median value and 3 times lower than the lower error bar). Various
scenarios to explain observed Xi enhancement are discussed. Arguments are given
in favor of the Xi production in direct reactions. The rates of the possible
production processes are estimated and compared.Comment: 13 pages, 3 figure
Strangeness Modes in Nuclei Tested by Anti-Neutrinos
Production of negative strangeness in reactions of inelastic anti-neutrino
scattering on a nucleus provides information on the modification of strange
degrees of freedom in nuclear matter. We calculate cross-sections of the
reaction channels and
\bar{\nu}_{e(\mu)} + p \to \Lb + e^+(\mu^+) and investigate their sensitivity
to the medium effects. In particular, we consider effects induced by the
presence of a low-energy excitation mode in the spectrum, associated with
the correlated -particle and proton-hole states, and the
renormalization of the weak interaction in medium. In order to avoid double
counting, various contributions to anti-neutrino scattering are classified with
the help of the optical theorem, formulated within the non-equilibrium Green's
function technique.Comment: 19 pages, 3 figures, feynMF diagram
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