Ab-initio coupled-cluster effective interactions for the shell model: Application to neutron-rich oxygen and carbon isotopes

We derive and compute effective valence-space shell-model interactions from ab-initio coupled-cluster theory and apply them to open-shell and neutron-rich oxygen and carbon isotopes. Our shell-model interactions are based on nucleon-nucleon and three-nucleon forces from chiral effective-field theory. We compute the energies of ground and low-lying states, and find good agreement with experiment. In particular our calculations are consistent with the N=14, 16 shell closures in oxygen-22 and oxygen-24, while for carbon-20 the corresponding N=14 closure is weaker. We find good agreement between our coupled-cluster effective-interaction results with those obtained from standard single-reference coupled-cluster calculations for up to eight valence neutrons

Spectroscopy of 24Al and extraction of Gamow-Teller strengths with the 24Mg(3He,t) reaction at 420 MeV

The 24Mg(3He,t)24Al reaction has been studied at E(3He)=420 MeV. An energy resolution of 35 keV was achieved. Gamow-Teller strengths to discrete levels in 24Al are extracted by using a recently developed empirical relationship for the proportionality between Gamow-Teller strengths and differential cross sections at zero momentum transfer. Except for small discrepancies for a few weak excitations, good agreement with previous 24Mg(p,n) data and nuclear-structure calculations using the USDA/B interactions in the sd shell-model space is found. The excitation energy of several levels in 24Al of significance for determination of the 23Mg(p,gamma)24Al thermonuclear reaction rate were measured. Results are consistent with two of the three previous (3He,t) measurements, performed at much lower beam energies. However, a new state at Ex(24Al)=2.605(10) MeV was found and is the third state above the proton separation energy.Comment: 6 pages, 4 figure

Neutron-proton asymmetry dependence of spectroscopic factors in Ar isotopes

Spectroscopic factors have been extracted for proton rich 34Ar and neutron rich 46Ar using the (p,d) neutron transfer reaction. The experimental results show little reduction of the ground state neutron spectroscopic factor of the proton rich nucleus 34Ar compared to that of 46Ar. The results suggest that correlations, which generally reduce such spectroscopic factors, do not depend strongly on the neutron-proton asymmetry of the nucleus in this isotopic region as was reported in knockout reactions. The present results are consistent with results from systematic studies of transfer reactions but inconsistent with the trends observed in knockout reaction measurements.Comment: 11 pages, 2 figures. submitted to PR

Erratum: Symmetry broken and restored coupled-cluster theory: II. Global gauge symmetry and particle number (2017 J. Phys. G: Nucl. Part. Phys. 44 015103)

Erratum: Symmetry broken and restored coupled-cluster theory: II. Global gauge symmetry and particle number (2017 J. Phys. G: Nucl. Part. Phys. 44 015103

Symmetry broken and restored coupled-cluster theory: II. Global gauge symmetry and particle number

44 pages, 16 figuresInternational audienceWe have recently extended many-body perturbation theory and coupled-cluster theory performed on top of a Slater determinant breaking rotational symmetry to allow for the restoration of the angular momentum at any truncation order (T. Duguet, $\it J. Phys. G: Nucl. Part. Phys.$ 42, 025107 (2015). Following a similar route, we presently extend Bogoliubov many-body perturbation theory and Bogoliubov coupled cluster theory performed on top of a Bogoliubov reference state breaking global gauge symmetry to allow for the restoration of the particle number at any truncation order. Eventually, formalisms can be merged to handle $SU(2)$ and $U(1)$ symmetries at the same time. Several further extensions of the newly proposed many-body formalisms can be foreseen in the mid-term future. The long-term goal relates to the $ab\ initio$ description of near-degenerate finite quantum systems with an open-shell character

Nonsudden Limits of Heavy-Ion Induced Knockout Reactions

We report on the single neutron and proton removal reactions from unstable nuclei with large asymmetry dS = Sn - Sp at incident energies below 80 MeV/nucleon. Strong non-sudden effects are observed in the case of deeply-bound-nucleon removal. The corresponding parallel momentum distributions exhibit an abrupt cutoff at high momentum that corresponds to an energy threshold occurring when the incident energy per particle is of comparable magnitude to the nucleon separation energy. A large low momentum tail is related to both dissipative processes and the dynamics of the nucleon removal process. New limits for the applicability of the sudden and eikonal approximations in nucleon knockout are given.status: publishe