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تسجيل مستخدم جديدHypertriton Electric Polarizability
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A rigorous formalism for determining the electric dipole polarizability of a three-hadron bound complex in the case that the system has only one bound (ground) state has been elaborated. On its basis, by applying a model wave function that takes into account specific features of the structure of the lightest hypernucleus and using the known low-energy experimental data for the p-n and lambda-d systems as input data, we have calculated the value of the electric dipole polarizability of the lambda hypertriton. It follows from our study that the polarizability of the lambda hypertriton is close to 3 fm^3 exceeding the polarizabilities of the ordinary three-nucleon nuclei by an order of magnitude.
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A simple analytical expression for the electric dipole polarizability of the three-hadron bound system having only one stable bound state has been derived neglecting by the higher orbital components of the off-shell three-body transition matrix at th
e energy of the bound state. As a case in point, we have estimated the electric dipole polarizability of the triton, using a cluster triton wave function and the Hulthen potential to describe the related p-n and n-d bound states.
The determination of nuclear symmetry energy, and in particular, its density dependence, is a long-standing problem for nuclear physics community. Previous studies have found that the product of electric dipole polarizability $alpha_D$ and symmetry e
nergy at saturation density $J$ has a strong linear correlation with $L$, the slope parameter of symmetry energy. However, current uncertainty of $J$ hinders the precise constraint on $L$. We investigate the correlations between electric dipole polarizability $alpha_D$ (or times symmetry energy at saturation density $J$) in Sn isotopes and the slope parameter of symmetry energy $L$ using the quasiparticle random-phase approximation based on Skyrme Hartree-Fock-Bogoliubov. A strong and model-independent linear correlation between $alpha_D$ and $L$ is found in neutron-rich Sn isotopes where pygmy dipole resonance (PDR) gives a considerable contribution to $alpha_D$, attributed to the pairing correlations playing important roles through PDR. This newly discovered linear correlation would help one to constrain $L$ and neutron-skin thickness $Delta R_textnormal{np}$ stiffly if $alpha_D$ is measured with high resolution in neutron-rich nuclei. Besides, a linear correlation between $alpha_D J$ in a nucleus around $beta$-stability line and $alpha_D$ in a neutron-rich nucleus can be used to assess $alpha_D$ in neutron-rich nuclei.
The nonmesonic decay of the hypertriton is calculated based on a hypertriton wavefunction and 3N scattering states, which are rigorous solutions of 3-body Faddeev equations using realistic NN and hyperon-nucleon interactions. The pion-exchange togeth
er with heavier meson exchanges for the $Lambda N to N N $ transition is considered. The total nonmesonic decay rate is found to be 0.5% of the free $Lambda$ decay rate. Integrated as well as differential decay rates are given. The p- and n- induced decays are discussed thoroughly and it is shown that the corresponding total rates cannot be measured individually.
Stimulated by recent indications that the binding energy of the hypertriton could be significantly larger than so far assumed, requirements of a more strongly bound $^3_Lambda {rm H}$ state for the hyperon-nucleon interaction and consequences for the
binding energies of $A=4,5$ and $7$ hypernuclei are investigated. As basis a $YN$ potential derived at next-to-leading order in chiral effective field theory is employed, Faddeev and Yakubovsky equations are solved to obtain the corresponding $3$- and $4$-body binding energies, respectively, and the Jacobi no-core shell model is used for $^5_Lambda$He and $^7_Lambda$Li. It is found that the spin-singlet $Lambda p$ interaction would have to be much more attractive which can be, however, accommodated within the bounds set by the available $Lambda p$ scattering data. The binding energies of the $^4_Lambda {rm He}$ hypernucleus are predicted to be closer to the empirical values than for $YN$ interactions that produce a more weakly bound $^3_Lambda {rm H}$. The quality of the description of the separation energy and excitation spectrum for $^7_Lambda$Li remains essentially unchanged.
The electric dipole strength distribution in Ca-48 between 5 and 25 MeV has been determined at RCNP, Osaka, from proton inelastic scattering experiments at forward angles. Combined with photoabsorption data at higher excitation energy, this enables f
or the first time the extraction of the electric dipole polarizability alpha_D(Ca-48) = 2.07(22) fm^3. Remarkably, the dipole response of Ca-48 is found to be very similar to that of Ca-40, consistent with a small neutron skin in Ca-48. The experimental results are in good agreement with ab initio calculations based on chiral effective field theory interactions and with state-of-the-art density-functional calculations, implying a neutron skin in Ca-48 of 0.14 - 0.20 fm.
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