No-core Shell Model/resonating-group Method Research Articles

Ab Initio NCSM/RGM for Three-Body Cluster Systems and Application to 4He+n+n

We introduce an extension of the ab initio no-core shell model/resonating group method (NCSM/RGM) in order to describe three-body cluster states. We present results for the 6He ground state within a 4He+n+n cluster basis as well as first results for the phase shifts of different channels of the 4He+n+n system which provide information about low-lying resonances of this nucleus.

Three-cluster dynamics within anab initioframework

We introduce a fully antisymmetrized treatment of three-cluster dynamics within the ab initio framework of the no-core shell model/resonating-group method (NCSM/RGM). Energy-independent non-local interactions among the three nuclear fragments are obtained from realistic nucleon-nucleon interactions and consistent ab initio many-body wave functions of the clusters. The three-cluster Schr\"odinger equation is solved with bound-state boundary conditions by means of the hyperspherical-harmonic method on a Lagrange mesh. We discuss the formalism in detail and give algebraic expressions for systems of two single nucleons plus a nucleus. Using a soft similarity-renormalization-group evolved chiral nucleon-nucleon potential, we apply the method to an $^4$He+$n+n$ description of $^6$He and compare the results to experiment and to a six-body diagonalization of the Hamiltonian performed within the harmonic-oscillator expansions of the NCSM. Differences between the two calculations provide a measure of core ($^4$He) polarization effects.

Structure of8B from elastic and inelastic7Be+pscattering

Background: Detailed experimental knowledge of the level structure of light weakly bound nuclei is necessary to guide the development of new theoretical approaches that combine nuclear structure with reaction dynamics.Purpose: The resonant structure of ${}^{8}$B is studied in this work.Method: Excitation functions for elastic and inelastic ${}^{7}$Be+$p$ scattering were measured using a ${}^{7}$Be rare isotope beam. Excitation energies ranging between 1.6 and 3.4 MeV were investigated. An $R$-matrix analysis of the excitation functions was performed.Results: New low-lying resonances at 1.9, 2.54, and 3.3 MeV in ${}^{8}$B are reported with spin-parity assignment 0${}^{+}$, 2${}^{+}$, and 1${}^{+}$, respectively. Comparison to the time-dependent continuum shell (TDCSM) model and ab initio no-core shell model/resonating-group method (NCSM/RGM) calculations is performed. This work is a more detailed analysis of the data first published as a Rapid Communication. J. P. Mitchell, G. V. Rogachev, E. D. Johnson, L. T. Baby, K. W. Kemper et al., [Phys. Rev. C 82, 011601(R) (2010)].Conclusions: Identification of the 0${}^{+}$, 2${}^{+}$, 1${}^{+}$ states that were predicted by some models at relatively low energy but never observed experimentally is an important step toward understanding the structure of ${}^{8}$B. Their identification was aided by having both elastic and inelastic scattering data. Direct comparison of the cross sections and phase shifts predicted by the TDCSM and ab initio no-core shell model coupled with the resonating group method is of particular interest and provides a good test for these theoretical approaches.

Unifiedab initioapproach to bound and unbound states: No-core shell model with continuum and its application to7He

We introduce a unified approach to nuclear bound and continuum states based on the coupling of the no-core shell model (NCSM), a bound-state technique, with the no-core shell model/resonating group method (NCSM/RGM), a nuclear scattering technique. This new ab initio method, no-core shell model with continuum (NCSMC), leads to convergence properties superior to either NCSM or NCSM/RGM while providing a balanced approach to different classes of states. In the NCSMC, the ansatz for the many-nucleon wave function includes (i) a square-integrable $A$-nucleon component expanded in a complete harmonic oscillator basis and (ii) a binary-cluster component with asymptotic boundary conditions that can properly describe weakly bound states, resonances, and scattering. The Schr\"odinger equation is transformed into a system of coupled-channel integral-differential equations that we solve using a modified microscopic $R$-matrix formalism within a Lagrange mesh basis. We demonstrate the usefulness of the approach by investigating the unbound ${}^{7}$He nucleus.

Ab initio many-body calculation of the [formula omitted] radiative capture

We apply the ab initio no-core shell model/resonating group method (NCSM/RGM) approach to calculate the cross section of the Be7(p,γ)B8 radiative capture. This reaction is important for understanding the solar neutrino flux. Starting from a selected similarity-transformed chiral nucleon–nucleon interaction that accurately describes two-nucleon data, we performed many-body calculations that simultaneously predict both the normalization and the shape of the S-factor. We study the dependence on the number of 7Be eigenstates included in the coupled-channel equations and on the size of the harmonic oscillator basis used for the expansion of the eigenstates and of the localized parts of the integration kernels. Our S-factor result at zero energy is on the lower side of, but consistent with, the latest evaluation.

Ab initiomany-body calculations of deuteron-He4scattering andLi6states

We extend the ab initio no-core shell model/resonating-group method (NCSM/RGM) to projectile-target binary-cluster states where the projectile is a deuteron. We discuss the formalism in detail and give algebraic expressions for the integration kernels. Using a soft similarity-renormalization-group evolved chiral nucleon-nucleon potential, we calculate deuteron-$^{4}\mathrm{He}$ scattering and investigate $^{6}\mathrm{Li}$ bound and unbound states. Virtual three-body breakup effects are obtained in an approximated way by including excited pseudostates of the deuteron in the calculation. We compare our results to experiment and to a standard NCSM calculation for $^{6}\mathrm{Li}$.