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Register a new userConstraints on the $Lambda$-neutron interaction from charge symmetry breaking in the $mathbf{^4_Lambda rm bf He}$--$mathbf{^4_Lambda rm bf H}$ hypernuclei
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We utilize the experimentally known difference of the $Lambda$ separation energies of the mirror hypernuclei ${^4_Lambda rm He}$ and ${^4_Lambda rm H}$ to constrain the $Lambda$-neutron interaction. We include the leading charge-symmetry breaking (CSB) interaction into our hyperon-nucleon interaction derived within chiral effective field theory at next-to-leading order. In particular, we determine the strength of the two arising CSB contact terms by a fit to the differences of the separation energies of these hypernuclei in the $0^+$ and $1^+$ states, respectively. By construction, the resulting interaction describes all low energy hyperon-nucleon scattering data, the hypertriton and the CSB in ${^4_Lambda rm He}$-${^4_Lambda rm H}$ accurately. This allows us to provide first predictions for the $Lambda$n scattering lengths, based solely on available hypernuclear data.
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The determination of the magnon diffusion length (MDL) is important for increasing the efficiency of spin Seebeck effect (SSE) based devices utilising non-metallic magnets. We extract the MDL at $50$ and $300,rm{K}$ in an $rm{Fe}_{3}rm{O}_{4}$ single crystal from the magnon dispersion obtained using inelastic neutron scattering (INS) and find them to be equal within error. We then measure the heat flux normalised SSE responses and in-plane magnetization of $rm{Fe}_{3}rm{O}_{4}$ thin films and normalise by the static magnetization contribution to the SSE before determining the MDLs from a fit of the thickness dependence. We find that the MDLs determined in this way are smaller than that measured from INS which maybe due to differences in magnon propagation between bulk and thin film $rm{Fe}_{3}rm{O}_{4}$.
We study the effects of final state interactions in the non-mesonic weak decay $Lambda N rightarrow nN$ (n is a neutron and N is either a neutron or a proton) of the hypernucleus $_Lambda^4$He. Using a three-body model the effects of distortion of the interaction of the emitted nucleon pair with the residual nucleus is considered. We also study the influence of the final state interaction between the emitted nucleons using the Migdal-Watson model. The effect of spin symmetries in the final state of the pair is also considered. Based on our calculations, we conclude that final state interactions play a minor role in the kinetic energy spectrum of the emitted nucleon pair.
To comprehend the recent Brookhaven National Laboratory experiment E788 on $^4_Lambda$He, we have outlined a simple theoretical framework, based on the independent-particle shell model, for the one-nucleon-induced nonmesonic weak decay spectra. Basically, the shapes of all the spectra are tailored by the kinematics of the corresponding phase space, depending very weakly on the dynamics, which is gauged here by the one-meson-exchange-potential. In spite of the straightforwardness of the approach a good agreement with data is acheived. This might be an indication that the final-state-interactions and the two-nucleon induced processes are not very important in the decay of this hypernucleus. We have also found that the $pi+K$ exchange potential with soft vertex-form-factor cutoffs $(Lambda_pi approx 0.7$ GeV, $Lambda_K approx 0.9$ GeV), is able to account simultaneously for the available experimental data related to $Gamma_p$ and $Gamma_n$ for $^4_Lambda$H, $^4_Lambda$He, and $^5_Lambda$He.
We report new measurements of the neutron charge form factor at low momentum transfer using quasielastic electrodisintegration of the deuteron. Longitudinally polarized electrons at an energy of 850 MeV were scattered from an isotopically pure, highly polarized deuterium gas target. The scattered electrons and coincident neutrons were measured by the Bates Large Acceptance Spectrometer Toroid (BLAST) detector. The neutron form factor ratio $G^{n}_{E}/G^{n}_{M}$ was extracted from the beam-target vector asymmetry $A_{ed}^{V}$ at four-momentum transfers $Q^{2}=0.14$, 0.20, 0.29 and 0.42 (GeV/c)$^{2}$.
{it Ab initio} calculation of the total cross section for the reactions $^{4}rm{He}(gamma,p)^3rm{H}$ and $^{4}rm{He}(gamma,n)^3rm{He}$ is presented, using state-of-the-art nuclear forces. The Lorentz integral transform (LIT) method is applied, which allows exact treatment of the final state interaction (FSI). The dynamic equations are solved using the effective interaction hyperspherical harmonics (EIHH) method. In this calculation of the cross sections the three-nucleon force is fully taken into account, except in the source term of the LIT equation for the FSI transition matrix element.
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