Testing microscopically derived descriptions of nuclear collectivity: Coulomb excitation of 22Mg

Abstract

Many-body nuclear theory utilizing microscopic or chiral potentials has developed to the point that collectivity might be dealt with in an ab initio framework without the use of effective charges; for example with the proper evolution of operators, or alternatively, through the use of an appropriate and manageable subset of particle-hole excitations.We present a precise determination of E2 strength in 22 Mg and its mirror 22 Ne by Coulomb excitation, allowing for rigorous comparisons with theory. No-core symplectic shell-model calculations were performed and agree with the new B(E2) values while in-medium similarity-renormalization-group calculations consistently underpredict the absolute strength, with the missing strength found to have both isoscalar and isovector components.

Nonempirical Interactions for the Nuclear Shell Model: An Update

“…Supporing this interpretation, unpublished calculations in a small space where exact diagonalizations are possible show unambiguously that the IMSRG(2) truncation misses a significant fraction of the E2 strength, and that capturing the full strength requires inclusion of correlated many-particle many-hole excitations. In addition, symmetry-adapted no-core shell model calculations of sd shell nuclei yielded significantly larger E2 strength using the same starting interaction (231).…”

“…IMSRG and CCEI/SMCC emerged (139,140,142,143,179). The VS-IMSRG, in particular, has been widely used to compute ground and excited-state energies (129,142,143,(225)(226)(227)(228)(229)(230)(231)(232)(233)(234)(235)(236)(237)(238), although theoretical uncertainties stemming from the method still prove challenging (see Sec. 6).…”

An ab-initio Gamow shell model approach with a core

“…We can see that the uses ofŜ -box up to the third order andQ-box up to the second order offer good descriptions of 24 O and 24 F. As a consequence, in the following calculations, we will use the one-bodyŜ -box up to the third order and the two-bodyQ-box up to the second order to construct the valence-space Hamiltonians within the GHF (Berggren) basis. Let us give a summary of the calculation procedure: (i) we start from the chiral NN interaction NNLO opt [40] expressed in 13 major HO shells with the commonly used oscillator frequency Ω = 20 − 24 MeV [34,46,47]; (ii) we perform GHF calculations using the NNLO opt potential to produce the Berggren single-particle basis. The neutron νd 3/2 , νp 1/2 , νp 3/2 and ν f 7/2 partial waves are treated in the GHF (Berggren) basis, while other neutron channels and all proton channels are handled in the traditional HF basis (i.e., obtained by diagonalizing the HF potential in a HO basis instead of in the Berggren basis).…”

Testing ab initio nuclear structure in neutron-rich nuclei: Lifetime measurements of second 2+ state in C16 and Ciemała1, Ziliani2, Crespi3 et al. 2020Phys. Rev. C161110View full textAdd to dashboardCite

“…Electric and magnetic γ decays provide a more demanding complementary test of theoretical approaches. So far, EM decays in light-and medium-mass systems have only been explored in few cases [24][25][26][27][28][29]. In contrast to energies or β decays, ab initio methods do not yet consistently describe all the data related to EM transitions.…”