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Register a new userThe Delta N -> NN transition in finite nuclei
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We perform a direct finite nucleus calculation of the partial width of a bound Delta isobar decaying through the non-mesonic decay mode, Delta N -> NN. This transition is modeled by the exchange of the long ranged pi meson and the shorter ranged rho meson. The contribution of this decay channel is found to be approximately 60 % of the decay width of the Delta particle in free space. Considering the additional pionic decay mode, we conclude that the total decay width of a bound Delta resonance in nuclei is of the order of 100 MeV and, consequently, no narrow Delta nuclear states exist, contrary to recent claims in the literature. Our results are in complete agreement with microscopic many-body calculations and phenomenological approaches performed in nuclear matter.
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Within the one boson exchange model, $Delta$-mass dependent M-matrix and its influence on the calculation of $NDelta to NN$ cross sections are investigated. Our calculations show that the $m_{Delta}$ dependence of $|textbf{p}_{NDelta}|$ and $|mathcal{M}|^2$ has effects on the calculations of $sigma_{NDeltato NN}$, especially around the threshold energy. We finally provide a table of accurate $sigma_{NDeltato NN}$ which can be used in the transport models.
We calculate the axial $Nto Delta(1232)$ and $Nto N^{star}(1440)$ transition form factors in a chiral constituent quark model. As required by the partial conservation of axial current ($PCAC$) condition, we include one- and two-body axial exchange currents. For the axial $Nto Delta(1232)$ form factors we compare with previous quark model calculations that use only one-body axial currents, and with experimental analyses. The paper provides the first calculation of all weak axial $Nto N^{star}(1440)$ form factors. Our main result is that exchange currents are very important for certain axial transition form factors. In addition to improving our understanding of nucleon structure, the present results are relevant for neutrino-nucleus scattering cross section predictions needed in the analysis of neutrino mixing experiments.
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.
In this paper, the in-medium $NNrightarrow NDelta$ cross section is calculated in the framework of the one-boson exchange model by including the isovector mesons, i.e. $delta$ and $rho$ mesons. Due to the isospin exchange in the $NNrightarrow NDelta$ process, the vector self-energies of the outgoing particles are modified relative to the incoming particles in isospin asymmetric nuclear matter, and it leads to the effective energies of the incoming $NN$ pair being different from the outgoing $NDelta$ pair. This effect is investigated in the calculation of the in-medium $NNrightarrow NDelta$ cross section. With the corrected energy conservation, the cross sections of the $Delta^{++}$ and $Delta^+$ channels are suppressed, and the cross sections of the $Delta^0$ and $Delta^-$ channels are enhanced relative to the results obtained without properly considering the potential energy changes. Our results further confirm the dependence of medium correction factor, $R=sigma_{ NNrightarrow NDelta}^*/sigma_{NNrightarrow NDelta}^{text{free}}$, on the charge state of $NNrightarrow NDelta$ especially around the threshold energy, but the isospin splitting of medium correction factor $R$ becomes weak at high beam energies.
We use an existing model of the $LambdaLambda N - Xi NN$ three-body system based in two-body separable interactions to study the $(I,J^P)=(1/2,1/2^+)$ three-body channel. For the $LambdaLambda$, $Xi N$, and $LambdaLambda - Xi N$ amplitudes we have constructed separable potentials based on the most recent results of the HAL QCD Collaboration. They are characterized by the existence of a resonance just below or above the $Xi N$ threshold in the so-called $H$-dibaryon channel, $(i,j^p)=(0,0^+)$. A three-body resonance appears {2.3} MeV above the $Xi d$ threshold. We show that if the $LambdaLambda - Xi N$ $H$-dibaryon channel is not considered, the $LambdaLambda N - Xi NN$ $S$ wave resonance disappears. Thus, the possible existence of a $LambdaLambda N - Xi NN$ resonance would be sensitive to the $LambdaLambda - Xi N$ interaction. The existence or nonexistence of this resonance could be evidenced by measuring, for example, the $Xi d$ cross section.
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