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Spectroscopic factors as a probe of nuclear shape in $^{44}$S via one-neutron knockout reaction

Ranojit Barman, Masaaki Kimura, Yoshiki Chazono, Kazuki Yoshida, Kazuyuki Ogata, Rajdeep Chatterjee

Abstract

Background: Neutron-rich nucleus $^{44}$S lies in the region where traditional $N=28$ shell closure weakens, leading to the emergence of shape coexistence and large-amplitude collective motion (LACM). Understanding the nature and degree of shape mixing in this nucleus remains an important and fascinating problem. Purpose: We investigate the manifestation of shape fluctuations in $^{44}$S and examine how the electric transitions and the spectroscopic factors from one-neutron knockout reactions can serve as probes of shapes mixing. Method: The antisymmetrized molecular dynamics combined with the generator coordinate method (AMD+GCM) is used to study the structure of $^{44}$S and $^{43}$S. Calculations are performed by using Gogny effective interactions with two different parameter sets, D1S and D1M, to explore the interaction dependence of shape mixing. Monopole and quadrupole transition strengths and spectroscopic factors are evaluated. The cross sections for the $^{44}$S$(p,pn)^{43}$S reaction are calculated within the distorted wave impulse approximation (DWIA). Results: The calculations reveal a strong interaction dependence of shape fluctuation in $^{44}$S. The structural differences obtained from D1S and D1M interactions produce distinct patterns of the electric transitions, the spectroscopic factors, and the cross sections for $^{44}$S$(p,pn)^{43}$S knockout reaction. Conclusion: The population of $3/2^-$ and $7/2^-$ states of $^{43}$S is particularly sensitive to the underlying shape fluctuation in $^{44}$S. Thus, the measurement of $^{44}$S$(p,pn)^{43}$S reaction can provide a direct experimental probe.

Spectroscopic factors as a probe of nuclear shape in $^{44}$S via one-neutron knockout reaction

Abstract

Background: Neutron-rich nucleus S lies in the region where traditional shell closure weakens, leading to the emergence of shape coexistence and large-amplitude collective motion (LACM). Understanding the nature and degree of shape mixing in this nucleus remains an important and fascinating problem. Purpose: We investigate the manifestation of shape fluctuations in S and examine how the electric transitions and the spectroscopic factors from one-neutron knockout reactions can serve as probes of shapes mixing. Method: The antisymmetrized molecular dynamics combined with the generator coordinate method (AMD+GCM) is used to study the structure of S and S. Calculations are performed by using Gogny effective interactions with two different parameter sets, D1S and D1M, to explore the interaction dependence of shape mixing. Monopole and quadrupole transition strengths and spectroscopic factors are evaluated. The cross sections for the SS reaction are calculated within the distorted wave impulse approximation (DWIA). Results: The calculations reveal a strong interaction dependence of shape fluctuation in S. The structural differences obtained from D1S and D1M interactions produce distinct patterns of the electric transitions, the spectroscopic factors, and the cross sections for SS knockout reaction. Conclusion: The population of and states of S is particularly sensitive to the underlying shape fluctuation in S. Thus, the measurement of SS reaction can provide a direct experimental probe.
Paper Structure (11 sections, 18 equations, 7 figures, 3 tables)

This paper contains 11 sections, 18 equations, 7 figures, 3 tables.

Table of Contents

  1. INTRODUCTION
  2. FORMALISM
  3. Framework of AMD+GCM
  4. Distorted Wave Impulse Approximation
  5. Results and discussion
  6. Large shape fluctuation of $^{44}$S and its interaction dependence
  7. Signature of large-amplitude collective motion in electromagnetic transitions
  8. Low-lying structures of $^{43}$S relevant to $^{44}\text{S}(p,pn)^{43}\text{S}$ reaction
  9. Overlap amplitudes and spectroscopic factors for the $^{44}\text{S}(p,pn)^{43}\text{S}$ reaction
  10. $^{44}\text{S}(p,pn)^{43}\text{S}$ at 250 MeV/nucleon
  11. Summary and conclusions

Figures (7)

  • Figure 1: The energy surfaces and GCM overlaps for the $0^+$ states of $^{44}$S obtained with (a) the Gogny D1S and (b) the Gogny D1M parameter sets. The contour lines represent the energies of the $0^+$ states at intervals of 1 MeV relative to their respective minima. The color plots show the values of the GCM overlap defined in Eq. \ref{['eq:ovlp']}. The filled white circles indicate the positions of the maximum GCM overlap.
  • Figure 2: Same as Fig. \ref{['fig:44S.J0+_ovlp']}, but for the $2^+$ states. The contour lines represent the energies obtained after the $K$ mixing, shown at an interval of 1 MeV with respect to their minimum energies.
  • Figure 3: Excitation spectra of $^{44}$S. Experimental data is taken from Santiago-Gonzalez_PhysRevC.83.061305.
  • Figure 4: Excitation spectra of $^{43}$S. Experimental data are taken from Refs. Longfellow2021_PRCMomiyama_43S.
  • Figure 5: The energy surfaces and GCM overlaps for the $1/2^-$, $3/2^-$, $5/2^-$ and $7/2^-$ states of $^{43}$S calculated with Gogny D1S effective interaction. The contour lines represent the energies of the $K$-mixed states at an interval of 1 MeV from their minimum energies. The filled white circles represent the maximum value of the GCM overlap.
  • ...and 2 more figures