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Register a new user$Lambda^+_c$- and $Lambda_b$-hypernuclei
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$Lambda^+_c$- and $Lambda_b$-hypernuclei are studied in the quark-meson coupling (QMC) model. Comparisons are made with the results for $Lambda$-hypernuclei studied in the same model previously. Although the scalar and vector potentials felt by the $Lambda$, $Lambda_c^+$ and $Lambda_b$ in the corresponding hypernuclei multiplet which has the same baryon numbers are quite similar, the wave functions obtained, e.g., for $1s_{1/2}$ state, are very different. The $Lambda^+_c$ baryon density distribution in $^{209}_{Lambda^+_c}$Pb is much more pushed away from the center than that for the $Lambda$ in $^{209}_Lambda$Pb due to the Coulomb force. On the contrary, the $Lambda_b$ baryon density distributions in $Lambda_b$-hypernuclei are much larger near the origin than those for the $Lambda$ in the corresponding $Lambda$-hypernuclei due to its heavy mass. It is also found that level spacing for the $Lambda_b$ single-particle energies is much smaller than that for the $Lambda$ and $Lambda^+_c$.
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We discuss low-lying collective excitations of $Lambda$ hypernuclei using the self-consistent mean-field approaches. We first discuss the deformation properties of $Lambda$ hypernuclei in the $sd$-shell region. Based on the relativistic mean-field (RMF) approach, we show that the oblate deformation for $^{28}$Si nucleus may disappear when a $Lambda$ particle is added to this nucleus. We then discuss the rotational excitations of $^{25}_{Lambda}$Mg nucleus using the three-dimensional potential energy surface in the deformation plane obtained with the Skyrme-Hartree-Fock method. The deformation of $^{25}_{Lambda}$Mg nucleus is predicted to be slightly reduced due to an addition of $Lambda$ particle. We demonstrate that this leads to a reduction of electromagnetic transition probability, $B(E2)$, in the ground state rotational band. We also present an application of random phase approximation (RPA) to hypernuclei, and show that a new dipole mode, which we call a soft dipole $Lambda$ mode, appears in hypernuclei, which can be interpreted as an oscillation of $Lambda$ particle against the core nucleus.
We present the first lattice-QCD calculation of the form factors governing the charm-baryon semileptonic decays $Lambda_c to Lambda^*(1520)ell^+ u_ell$. As in our previous calculation of the $Lambda_b to Lambda^*(1520)$ form factors, we work in the $Lambda^*(1520)$ rest frame, but here we use four different heavy-baryon momenta instead of just two. Because of the lower mass of the $Lambda_c$, the moderately-sized momenta used here are sufficient to determine the form factors in the full kinematic range of the semileptonic decay. We also update the analysis of our lattice results for the $Lambda_b to Lambda^*(1520)$ and $Lambda_b to Lambda_c^*(2595,2625)$ form factors by imposing exact relations among the different form factors at zero recoil that follow from rotational symmetry. Imposing these relations ensures the correct behavior of the angular observables near the endpoint.
We calculate the $Lambda Lambda to YN$ transition rate of ${^{phantom{Lambda}6}_{Lambda Lambda}}$He by the hybrid picture, the $pi$ and $K$ exchanges plus the direct quark processes. It is found that the hyperon-induced decay is weaker than the nucleon-induced decay, but the former may reveal the short-range mechanism of the weak transition and also give a clear signal of the strong $Delta I=3/2$ transition. The $Lambda Lambda to Y N$ transition in double-$Lambda$ hypernucleus is complement to the $Lambda N to NN$ transition as it occurs only in the J=0 channel, while the J=1 transition is dominant in the $Lambda N to NN$ case.
Within a combined approach we investigate the main features of the production of hyper-fragments in relativistic heavy-ion collisions. The formation of hyperons is modelled within the UrQMD and HSD transport codes. To describe the hyperon capture by nucleons and nuclear residues a coalescence of baryons (CB) model was developed. We demonstrate that the origin of hypernuclei of various masses can be explained by typical baryon interactions, and that it is similar to processes leading to the production of conventional nuclei. At high beam energies we predict a saturation of the yields of all hyper-fragments, therefore, this kind of reactions can be studied with high yields even at the accelerators of moderate relativistic energies.
We extend the relativistic point coupling model to single-$Lambda$ hypernuclei. For this purpose, we add $N$-$Lambda$ effective contact couplings to the model Lagrangian, and determine the parameters by fitting to the experimental data for $Lambda$ binding energies. Our model well reproduces the data over a wide range of mass region although some of our interactions yield the reverse ordering of the spin-orbit partners from that of nucleons for heavy hypernuclei. The consistency of the interaction with the quark model predictions is also discussed.
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