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Register a new userMagnetic moments of the octet, low-lying charm, and low-lying bottom baryons in a nuclear medium
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Authors
Kazuo Tsushima
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We study the magnetic moments of the octet, low-lying charm, and low-lying bottom baryons with nonzero light quarks in symmetric nuclear matter. This is the first study of estimating the medium modifications of magnetic moments for these low-lying charm and bottom baryons.
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In-medium properties of the low-lying strange, charm, and bottom baryons in symmetric nuclear matter are studied in the quark-meson coupling (QMC) model. Results for the Lorentz-scalar effective masses, mean field potentials felt by the light quarks in the baryons, in-medium bag radii, and the lowest mode bag eigenvalues are presented for those calculated using the updated data. This study completes the in-medium properties of the low-lying baryons in symmetric nuclear matter in the QMC model, for the strange, charm and bottom baryons which contain one or two strange, one charm or one bottom quarks, as well as at least one light quark. Highlight is the prediction of the bottom baryon Lorentz-scalar effective masses, namely, the Lorentz-scalar effective mass of $Sigma_b$ becomes smaller than that of $Xi_b$ at moderate nuclear matter density, $m^*_{Sigma_b} < m^*_{Xi_b}$, although in vacuum $m_{Sigma_b} > m_{Xi_b}$. We study further the effects of the repulsive Lorentz-vector potentials on the excitation (total) energies of these bottom baryons.
In-medium properties of the low-lying baryons are studied in the quark-meson coupling (QMC) model, focusing on the $Sigma_b$ and $Xi_b$ baryons. It is predicted that the Lorentz-scalar effective mass of $Sigma_b$ becomes smaller than that of $Xi_b$ at moderate nuclear matter density, and as the density increases, namely, $m^*_{Sigma_b} < m^*_{Xi_b}$, although in vacuum $m_{Sigma_b} > m_{Xi_b}$. We also study the effects of the repulsive Lorentz-vector potentials on the excitation energies of these bottom baryons.
The strong and radiative decays of the low-lying $lambda$-mode $D$-wave $Lambda_{c(b)}$, $Sigma_{c(b)}$, $Xi_{c(b)}$, $Xi_{c(b)}$, and $Omega_{c(b)}$ baryons are studied in a constituent quark model. Our calculation shows the following: (i) The missing $lambda$-mode $D$-wave $Omega_{c(b)}$, $Lambda_{b}$, and $Xi_{b}$ baryons have a relatively narrow decay width of a few MeV or a few tens of MeV and their dominant strong and radiative decay channels can be ideal for searching for their signals in future experiments. (ii) The $lambda$-mode $1D$-wave excitations in the $Sigma_{c(b)}$ and $Xi_{c(b)}$ families appear to have a relatively broad width of $sim 50-200$ MeV.Most of the $1D$-wave states have large decay rates into the $1P$-wave heavy baryons via the pionic or kaonic strong decay processes, which should be taken seriously in future observations. (iii) Both $Lambda_c(2860)$ and $Xi_c(3050)$ seem to favor the $J^P=3/2^+$ excitation $|^2D_{lambdalambda} frac{3}{2}^+ rangle$ of $bar{mathbf{3}}_F$, while both $Lambda_c(2880)$ and $Xi_c(3080)$ may be assigned as the $J^P=5/2^+$ excitation $|^2D_{lambdalambda} frac{5}{2}^+ rangle$ of $bar{mathbf{3}}_F$. The nature of $Xi_c(3050)$ and $Xi_c(3080)$ could be tested by the radiative transitions $Xi_c(3055)^0to Xi_c(2790)^0 gamma$ and $Xi_c(3080)^0 to Xi_c(2815)^0 gamma$, respectively.
In situations where the low lying eigenmodes of the Dirac operator are suppressed one observed degeneracies of some meson masses. Based on these results a hidden symmetry was conjectured, which is not a symmetry of the Lagrangian but emerges in the quantization process. We show here how the difference between classes of meson propagators is governed by the low modes and shrinks when they disappear.
We present a calculation of low energy magnetic states of doubly-closed-shell nuclei. Our results have been obtained within the random phase approximation using different nucleon-nucleon interactions, having zero- or finite-range and including a possible contribution in the tensor channel.
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