K+^+ production in proton-nucleus reactions and the role of momentum-dependent potentials

The production of $K^+$ mesons in proton-nucleus collisions from 1.0 to 2.5 GeV is analyzed with respect to one-step nucleon-nucleon $(NN\to N Y K^+$) and two-step $\Delta$-nucleon $(\Delta N \to K^+ Y N$) or pion-nucleon $(\pi N \to K^+ Y$) production channels on the basis of a coupled-channel transport approach (CBUU) including the kaon final state interactions. The influence of momentum-dependent potentials for the nucleon, hyperon and kaon in the final state are studied as well as the importance of $K^+$ elastic rescattering in the target nucleus. The transport calculations are compared to the experimental $K^+$ spectra taken at LBL Berkeley, SATURNE, CELSIUS, GSI and COSY-J\"ulich. It is found that the momentum-dependent baryon potentials effect the excitation function of the $K^+$ cross section; at low bombarding energies of $\sim$ 1.0 GeV the attractive baryon potentials in the final state lead to a relative enhancement of the kaon yield whereas the net repulsive potential at bombarding energies $\sim$ 2 GeV causes a decrease of the $K^+$ cross section. Furthermore it is pointed out, that especially the $K^+$ spectra at low momenta (or kinetic energy $T_K$) allow to determine the in-medium $K^+$ potential almost model independently due to a relative shift of the $K^+$ spectra in kinetic energy that arises from the acceleration of the kaons when propagating out of the nuclear medium to free space, i.e. converting potential energy to kinetic energy of the free kaon.Comment: 11 pages, LaTeX, including 10 postscript figures, submitted to Eur. Phys. J.

Heavy Hyperon--Antihyperon Production

Based on the experience from the production of anti-Lambda Lambda and anti-Sigma Sigma pairs at LEAR (experiment PS185) it is suggested to continue the investigations towards the heavier antihyperon--hyperon pairs anti-Xi Xi and anti-Omega Omega in view of: (1) the production dynamics of the heavier antihyperon--hyperon out of the anti-p p annihilation (2) a comparison of the (3s 3anti-s quark system) anti-Omega Omega to the (3 (anti-s s)) 3 phi meson production, where both systems have similar masses (3.345 and 3.057, respectively) and identical valence quark content. A systematic study of the antihyperon--hyperon production with increasing strangeness content is interesting for the following reasons: The anti-Omega Omega production is the creation of two spin 3/2 objects out of the two spin 1/2 anti-p p particles. Results of the PS185 experiments prove a clear dominance of the spin triplet anti-s s dissociation. In the Omega anti-Omega the three s-quarks (three anti-s quarks) are aligned to spin 3/2 each. If the three anti-s s pairs are now all in spin triplet configurations when created out of the gluonic interaction they should have spin parity quantum number as 3^- as long as Omega anti-Omega is created with relative L=0 angular momentum. The comparison of the Omega anti-Omega baryon pair to the phi phi phi three meson production (where the three anti-s s quark pairs might not but can be produced without relative correlation) would provide a unique determination of the intermediate matter state. Measurements of excitation functions and polarization transfers should be used to examine these gluon rich anti-p p --> anti-Omega Omega and anti-p p --> phi phi phi reaction channels. Such experiments should be performed at the PANDA detector at the FAIR facility of the GSI.Comment: 4 pages, 2 figures, Presented at LEAP05: International Conference on Low Energy Antiproton Physics, Bonn - Juelich, Germany, May 16-22, 200

Transport analysis of K+ production in proton-nucleus reactions

The production of $K^+$ mesons in proton-nucleus collisions from 1.0 to 2.3 GeV is analyzed with respect to one-step nucleon-nucleon $(NN\to N Y K^+$) and two-step $\Delta$-nucleon $(\Delta N \to K^+ Y N$) or pion-nucleon $(\pi N \to K^+ Y$) production channels on the basis of a coupled-channel transport approach (CBUU) including the kaon final-state-interactions (FSI). Momentum-dependent potentials for the nucleon, hyperon and kaon in the final state are included as well as $K^+$ elastic rescattering in the target nucleus. The transport calculations are compared to the experimental $K^+$ spectra taken at COSY-J\"ulich. Our systematic analysis of $K^+$ spectra from $^{12}C$, $^{63}Cu$, $^{107}Ag$ and $^{197}Au$ targets as well as their momentum differential ratios gives a repulsive $K^+$ potential of $20\pm 5$ MeV at normal nuclear matter density.Comment: 7 pages, 5 figures, submitted to Eur. Phys. J.

Compound nucleus contribution to the alpha particle scattering on 28Si nuclei

Compound nucleus contribution to the elastic and inelastic scattering of alpha particles on 28Si nuclei is estimated. The analysis is based on the Hauser-Feshbach theory of compound reactions. For two selected alpha particle energies the experimental energy averaged angular distributions are compared with those calculated as an incoherent sum of direct and compound nucleus (for ground and 1.78 MeV states) or pure compound nucleus (for 4.61 MeV state) cross-sections

Six-nucleon spectroscopic amplitudes for 1p - shell nuclei. Pt. 2 Calculations and applications

Spectroscopic amplitudes for separation of six-nucleon clusters in low-lying states corresponding to the (ls)4(lp)2 shell-model configuration were calculated for lp-shell nuclei. The calculations were performed with the aid of intermediate-coupling model wave functions. The selectivity in excitation of the states produced in six-nucleon cluster transfer reactions with lp-shell nuclei is discussed. Sum rules for six-nucleon pickup and stripping are given

The lifetime of the Lambda hyperon bound in hypernuclei produced by p+U collisions

The nonmesonic decay of the Lambda hyperon has been investigated by observation of delayed fission from heavy hypernuclei produced in proton-U collisions at Tp = 1.9 GeV. The lifetime of heavy hypernuclei with masses A approximately 220 obtained in the present work, i.e. tau = 138 +- 6 (stat.) +-m 17 (syst.) ps, is the most accurate result for heavy hypernuclei produced in proton and antiproton induced collisions on a U target so far. PACS: {13.30.-a}{Decays of baryons} {13.75.Ev}{Hyperon-nucleon interaction} {21.80}{Hypernuclei} {25.80.Pw}{Hyperon-induced reactions}Comment: 16 pages, 4 Postscript figures, uses file appolb.cls (included), submitted to Acta Physica Polonica B, http://th-www.if.uj.edu.pl/act

On the Delta I = 1/2 rule in the Lambda N ----> N N reaction

It is shown that the mass dependence of the $\Lambda$-lifetime in heavy hypernuclei is sensitive to the ratio of neutron-induced to proton-induced non-mesonic decay rates R_n/R_p. A comparison of the experimental mass dependence of the lifetimes with the calculated ones for different values of R_n/R_p leads to the conclusion that this ratio is larger than 2 on the confidence level of 0.75. This suggests that the phenomenological $\Delta$I=1/2 rule might be violated for the nonmesonic decay of the $\Lambda$-hyperon.Comment: 3 pages, 2 figures, to be published in European Physical Journal

The optical model and distorted-wave analysis of cross-sections for the scattering of the 24-28 MeV alpha particles from 28Si

The interaction of alpha particles with nuclei is still not well understood [1, 2]. In particular, difficulties arise in the scattering on A = 4n nuclei [3]. It seems that a simultaneous analysis of the elastic and inelastic processes permits solving some of these problems. Our analysis is based on the experimental data for the elastic and inelastic scattering of alpha particles on 28Si nuclei, obtained with the Cracow U-120 cyclotron. The angular distributions for the elastic [4] and inelastic [5] scattering leading to the first two excited states in 28Si were measured for the alpha bombarding energies of 24, 25, 26, 26.5, 27 and 28 MeV in the angular range from 2 5 ' to 179' (in lab system). The elastic process was described by means of the optical model and the inelastic one by the distorted wave theory. The possibility of resolving some of the optical model ambiguities was studied

l-dependent resonance absorption in the optical model description of alpha particle elastic scattering

The interaction of alpha particles with atomic nuclei is a useful tool for the investigation of the reaction mechanism and the structure of nucleus. Many experiments concerning the elastic scattering of alpha particles on atomic nuclei show some phenomena which are not fully understood [1-3]. Earlier investigations of the elastic alpha particle scattering from 12C [4, 5], ieO [4, 6], 20Ne [8], 24Mg [7, 8], 28Si [9, 10] and 40Ca [11-13] have revealed a strong energy dependence of the backward cross-section. The confrontation of theoretical predictions with the experiments shows that for these nuclei it is rather difficult to obtain good optical model fits to the elastic differential cross-sections in the full range of the scattering angles[…