We investigate the impact of ambiguities coming from the choice of optical potentials and nucleon-nucleon scattering cross sections on the spectroscopic factors extracted from the $^{12}$C($p$,$2p$)$^{11}$B reaction. These ambiguities are evaluated b
y analyzing the cross sections of the $^{12}$C($p$,$2p$)$^{11}$B reaction at 100 and 200 MeV within the framework of the distorted-wave impulse approximation with realistic choices of nuclear inputs. The results show that the studied ambiguities are considerably large in this energy region and careful choices of nuclear inputs used in the reaction calculations are required to extract reliable structure information.
The hadron-deuteron correlation function has attracted many interests as a potential method to access the three-hadron interactions. However, the weakly-bound nature of deuteron has not been considered in the preceding studies. In this study, the bre
akup effect of deuteron on the deuteron-$Xi^-$ ($d$-$Xi^-$) correlation function $C_{dXi^-}$ is investigated. The $d$-$Xi^-$ scattering is described by a nucleon-nucleon-$Xi$ three-body reaction model. The continuum-discretized coupled-channels method, which is a fully quantum-mechanical and non-perturbative reaction model, is adopted. $C_{dXi^-}$ turns out to be sensitive to the strong interaction and enhanced by the deuteron breakup effect by 6--8 % for the $d$-$Xi^-$ relative momentum below about 70 MeV/$c$. Low-lying neutron-neutron continuum states are responsible for this enhancement. Within the adopted model, the deuteron breakup effect on $C_{dXi^-}$ is found to be appreciable but not very significant. Except for the enhancement by several percent, studies on $C_{dXi^-}$ without the deuteron breakup effect can be justified.
Background: The triaxial and hexadecapole deformations of the K=0+ and K=2+ bands of 24Mg have been investigated by the inelastic scatterings of various probes, including electrons, protons, and alpha particles, for a prolonged time. However, it has
been challenging to explain the unique properties of the scatterings observed for the $4^+_1$ state through reaction calculations. Purpose: To investigate the structure and transition properties of the K=0+ and K=2+ bands of 24Mg employing the microscopic structure and reaction calculations via inelastic proton and alpha-scattering. Particularly, the E4 transitions to the $4^+_1$ and $4^+_2$ states were reexamined. Method: The structure of 24Mg was calculated employing the variation after the parity and total-angular momentum projections in the framework of the antisymmetrized molecular dynamics(AMD). The inelastic proton and alpha reactions were calculated by the microscopic coupled-channel (MCC) approach by folding the Melbourne g-matrix NN interaction with the AMD densities of 24Mg. Results: Reasonable results were obtained on the properties of the structure, including the energy spectra and E2 and E4 transitions of the K=0+ and K=2+ bands owing to the enhanced collectivity of triaxial deformation. The MCC+AMD calculation successfully reproduced the angular distributions of the $4^+_1$ and $4^+_2$ cross sections of proton scattering at incident energies of $E_p$=40--100MeV and alpha-scattering at $E_alpha$=100--400MeV. Conclusions: This is the first microscopic calculation that described the unique properties of the $0^+_1to 4^+_1$ transition. In the inelastic scattering to the $4^+_1$ state, the dominant two-step process of the $0^+_1to 2^+_1to 4^+_1$ transitions and the deconstructive interference is the weak one-step process were essential.
[Background:] The band structure of the negative-parity states of $^{24}$Mg has not yet been clarified. The $K^pi=0^-$, $K^pi=1^-$, and $K^pi=3^-$ bands have been suggested, but the assignments have been inconsistent between experiments and theories.
[Purpose:] Negative-parity states of $^{24}$Mg are investigated by microscopic structure and reaction calculations via proton and alpha inelastic scattering to clarify the band assignment for the observed negative-parity spectra. [Method:] The structure of $^{24}$Mg was calculated using the antisymmetrized molecular dynamics~(AMD). Proton and alpha inelastic reactions were calculated using microscopic coupled-channel (MCC) calculations by folding the Melbourne $g$-matrix $NN$ interaction with the AMD densities of $^{24}$Mg. [Results:] The member states of the $K^pi=0^+$, $K^pi=2^+$, $K^pi=0^-$, $K^pi=1^-$, and $K^pi=3^-$ bands of $^{24}$Mg were obtained through the AMD result. In the MCC+AMD results for proton and alpha elastic and inelastic cross sections, reasonable agreements were obtained with existing data, except in the case of the $4^+_1$ state. [Conclusions:] The $3^-$ state of the $K^pi=3^-$ band and the $1^-$ and $3^-$ states of the $K^pi=0^-$ bands were assigned to the $3^-_1$(7.62 MeV), $1^-_1$(7.56 MeV), and $3^-_2$(8.36 MeV) states, respectively. The present AMD calculation is the first microscopic structure calculation to reproduce the energy ordering of the $K^pi=0^-$, $K^pi=1^-$, and $K^pi=3^-$ bands of $^{24}$Mg.
Background: In the continuum-discretized coupled-channel method, a breakup cross section (BUX) is obtained as an admixture of several components of different channels in multi-channel scattering. Purpose: Our goal is to propose an approximate way of
decomposing the discretized BUX into components of each channel. This approximation is referred to as the probability separation (P-separation). Method: As an example, we consider $^{11}$Be scattering by using the three-body model with core excitation ($^{10}mathrm{Be}+n+mathrm{T}$, where T is a target). The structural part is constructed by the particle-rotor model and the reaction part is described by the distorted wave Born approximation (DWBA). Results: The validity of the P-separation is tested by comparing with the exact calculation. The approximate way reproduces the exact BUXs well regardless of the configurations and/or the resonance positions of $^{11}$Be. Conclusion: The method proposed here can be an alternative approach for decomposing discretized BUXs into components in four- or five-body scattering where the strict decomposition is hard to perform.
The virtual photon theory (VPT), which is based on first-order Coulomb dissociation restricted to the electric dipole ($E1$), has been successfully used to explain the breakup data for several cases. Our aim is to study the role of various higher-ord
er processes that are ignored in the VPT, such as the nuclear breakup, interference between nuclear and Coulomb amplitudes, and multistep breakup processes mainly due to strong continuum-continuum couplings in the breakup of two-body projectiles on a heavy target at both intermediate and higher incident energies. For the purpose of numerical calculations, we employed eikonal version of three-body continuum-discretized coupled-channels (CDCC) reaction model. Our results for the breakup of $^{11}$Be and $^{17}$F on $^{208}$Pb target at 100, 250, and 520 MeV/A, show the importance of nuclear breakup contribution, and its significant role in the multistep processes. The multistep effect on Coulomb breakup for core-neutron projectile was found to be negligible, whereas it was important for core-proton projectile. Coulomb-nuclear interference (CNI) effect was also found to be non-negligible. Quantitatively, the multistep effects due to the nuclear breakup was found to depend on the incident energy through the energy dependence of the core-target and nucleon-target nuclear potentials. The nuclear breakup component, the CNI effect, and the multistep breakup processes are all found to be non-negligible; hence, the assumptions adopted in the VPT for the accurate description of breakup cross sections are not valid.
The correspondence between the isoscalar monopole (IS0) transition strengths and $alpha$ inelastic cross sections, the $B({rm IS0})$-$(alpha,alpha)$ correspondence, is investigated for $^{24}$Mg($alpha,alpha$) at 130 and 386 MeV. We adopt a microscop
ic coupled-channel reaction framework to link structural inputs, diagonal and transition densities, for $^{24}$Mg obtained with antisymmetrized molecular dynamics to the ($alpha,alpha$) cross sections. We aim at clarifying how the $B({rm IS0})$-$(alpha,alpha)$ correspondence is affected by the nuclear distortion, the in-medium modification to the nucleon-nucleon effective interaction in the scattering process, and the coupled-channels effect. It is found that these effects are significant and the explanation of the $B({rm IS0})$-$(alpha,alpha)$ correspondence in the plane wave limit with the long-wavelength approximation, which is often used, makes no sense. Nevertheless, the $B({rm IS0})$-$(alpha,alpha)$ correspondence tends to remain because of a strong constraint on the transition densities between the ground state and the $0^+$ excited states. The correspondence is found to hold at 386 MeV with an error of about 20%-30%, while it is seriously stained at 130 MeV mainly by the strong nuclear distortion. It is also found that when a $0^+$ state that has a different structure from a simple $alpha$ cluster state is considered, the $B({rm IS0})$-$(alpha,alpha)$ correspondence becomes less valid. For a quantitative discussion on the $alpha$ clustering in $0^+$ excited states of nuclei, a microscopic description of both the structure and reaction parts will be necessary.
The discovery of gravitational waves has confirmed old theoretical predictions that binary systems formed with compact stars play a crucial role not only for cosmology and nuclear astrophysics. As a byproduct of these and subsequent observations, it
is now clear that neutron-star mergers can be a competitive site for the production of half of the elements heavier than iron in the universe following a sequence of fast neutron capture reactions known as the r process. In this article we discuss an effect which has been so far neglected in calculations of r-process nucleosynthesis in neutron star mergers. We show that the corrections due to the neutron environment even at relatively small neutron densities, within the bounds of numerical hydrodynamical simulations of neutron star mergers and after the onset of the r process, are non-negligible and need to be taken into account to accurately describe the elemental abundance as determined by observations.
Background: Proton-induced nucleon knockout $(p,pN)$ reactions have been successfully used to study the single-particle nature of stable nuclei in normal kinematics with the distorted-wave impulse approximation (DWIA) framework. Recently, these react
ions have been applied to rare-isotope beams at intermediate energies in inverse kinematics to study the quenching of spectroscopic factors. Purpose: Our goal is to investigate the effects of various corrections and uncertainties within the standard DWIA formalism on the $(p,pN)$ cross sections. The consistency of the extracted reduction factors between DWIA and other methods is also evaluated. Method: We analyze the $(p,2p)$ and $(p,pn)$ reactions data measured at the R$^3$B/LAND setup at GSI for carbon, nitrogen, and oxygen isotopes in the incident energy range of 300--450 MeV/u. Cross sections and reduction factors are calculated by using the DWIA method. The transverse momentum distribution of the $^{12}$C($p$,$2p$)$^{11}$B reaction is also investigated. Results: We have found that including the nonlocality corrections and the Mo ller factor affects the cross sections considerably. The proton-neutron asymmetry dependence of reduction factors extracted by the DWIA calculation is very weak and consistent with those given by other reaction methods and textit{ab initio} structure calculations. Conclusions: The results found in this work provide a detailed investigation of the DWIA method for $(p,pN)$ reactions at intermediate energies. They also suggest that some higher-order effects, which is essential for an accurate cross-section description at large recoil momentum, is missing in the current DWIA and other reaction models.
Recently, we have determined surface distributions of $alpha$ clusters in the ground state of $^{20}mathrm{Ne}$ from $alpha$-transfer cross sections, without investigating the properties of its excited states. In this paper we extend our comprehensio
n of $alpha$-cluster structures in excited states of nuclei through reaction studies. In particular we focus on $^{16}mathrm{O}$, for which attention has been paid to advances of structure theory and assignment regarding $4^+$-resonance states. We study the surface manifestation of the $alpha$-cluster states in both the ground and excited states of $^{16}mathrm{O}$ from the analysis of the $alpha$-transfer reaction $^{12}mathrm{C}(^6mathrm{Li},d)^{16}mathrm{O}$. The $alpha$-transfer reaction is described by the distorted-wave Born approximation. We test two microscopic wave functions as an input of reaction calculations. Then a phenomenological potential model is introduced to clarify the correspondence between cluster-wave functions and transfer-cross sections. Surface peaks of the $alpha$-wave function of $^{16}mathrm{O}(0^+)$ are sensitively probed by transfer-cross sections at forward angles, while it remains unclear how we trace the surface behavior of $^{16}mathrm{O}(4^+)$ from the cross sections. We are able to specify that the $alpha$-cluster structure in the $0_1^+$ and $0_2^+$ states prominently manifests itself at the radii $sim 4$ and $sim 4.5$~fm, respectively. It is remarkable that the $4_1^+$ state has the $^{12}mathrm{C}+alpha$-cluster component with the surface peak at the radius $sim 4$ or outer, whereas the $^{12}mathrm{C}+alpha$-cluster component in the $4_2^+$ state is found not to be dominant. The $4_2^+$ state is difficult to be interpreted by a simple potential model assuming the $^{12}mathrm{C}+alpha$ configuration only.
