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Latest Results for Few-Body Systems

19 April 2024

• Positronium Negative Ion Embedded in Non-ideal Classical Plasmas: Doubly Excited Singlet S States

  Abstract

  The effects of the non-ideality (NI) of the classical plasmas on the doubly excited singlet S states in the positronium negative ion (Ps \(^-\) ) are investigated. The organised effect of the plasma is taken care of by means of a pseudopotential which is characterised by the Debye length D and the non-ideality parameter \(\gamma \) . Using an extensive wavefunction within the framework of the stabilization method, it has been possible to identify four doubly excited states (DES) in Ps \(^-\) . The convergence of the energy and the width of those states are corroborated by increasing the number of terms in the wavefunction. Our present calculation for the plasma-free case reproduces the established results. An inclusive study is made to quantify and qualify the changes experienced by the energies and the widths of those states due to the influence of the NI over a wide range. It is observed that the energy of each DES increases and the width of each DES diminishes due to the effect of the increasing NI of the plasma.

• Experiments of Few-Nucleon Scattering to Explore Three-Nucleon Forces

  Abstract

  Few-nucleon scattering offers a good opportunities to study dynamical aspects of three-nucleon forces, that are momentum, spin and isospin dependent. In the paper, the experimental results of deuteron-proton elastic scattering at \(\sim ~\mathrm 100\) MeV/nucleon obtained in the course of the study are presented. The experimental study of few-nucleon scattering has been recently extended to the proton- \(^3 \textrm{He}\) scattering with the aim of approaching the isospin \(T=3/2\) channel in three-nucleon forces. The data are in comparison with the rigorous numerical calculations based on state-of-the-art nuclear potentials with three-nucleon forces.

• Impact of the $$\hbox {N}^4\hbox {LO}$$ Short-Range Three-Nucleon Force Components on the Nucleon-Deuteron Spin Correlation Coefficients

  Abstract

  The spin correlation coefficients in the neutron-deuteron elastic scattering process at incoming neutron laboratory energies \(\hbox {E}=10\) , 135, 190, and 250 MeV are determined by solving the momentum space three-nucleon (3N) Faddeev equations. The chiral two-nucleon (2N) interaction with momentum-space semi-local (SMS) regularization up to the fifth order of chiral expansion ( \(\hbox {N}^4\hbox {LO}\) ), supplemented by the F-waves terms from the sixth order ( \(\hbox {N}^5\hbox {LO}\) ), is used. Additionally, the consistent 3N force (3NF) at the third order of chiral expansion, supplemented by the short-range contributions from \(\hbox {N}^4\hbox {LO}\) is applied. As a results, we give predictions for the complete set of spin correlation coefficients \(C_{\alpha ,\beta }\) . We find that the effect of the investigated three-nucleon \(\hbox {N}^4\hbox {LO}\) components amounts up to several dozen percent, depending on reaction energy, scattering angle and type of spin correlation coefficient itself. Our results can serve as a guide for future measurements of the spin correlation coefficients.