**Convergence of ab initio calculated M1 observables: The role of symmetry, structure, and selection rules**

Zhou Zhou, Graduate Student, University of Notre Dame

Electromagnetic observables provide probes for nuclear structure. In particular, M1 observables provide information on angular momentum structure. Ab initio no-core shell model (NCSM) calculations for light (p-shell) nuclei provide predictions for M1 observables. In order to understand how the predicted M1 moments and transition strengths relate to the underlying structure of the nucleus, the contributions of the diﬀerent components of the M1 operator (orbital and spin, broken into isoscalar and isovector parts) are studied. Each of these components is subject to diﬀerent selection rules on angular momentum (orbital and spin) and isospin quantum numbers. The joint Lanczos decomposition method is applied to determine the dominant L and S contributions to the calculated wave functions and thus understand the relevant selection rules for each transition. In this seminar, the convergence properties of NCSM calculations for M1 observables, including the role of symmetry, structure, and selection rules, will be discussed.

and

**Basis truncation schemes in the symplectic no-core configuration interaction framework**

Jakub Herko, Graduate Student, University of Notre Dame

The no-core configuration interaction (NCCI) framework, also known as the no-core shell model, is an ab initio method predicting properties of light nuclei from the underlying internucleon interaction. However, the dimension of the NCCI model space rapidly increases with the maximal number of allowed excitation oscillator quanta and the number of nucleons, which limits the convergence of calculated observables that can be achieved in practice. To obtain more converged results we can make use of the approximate Sp(3,R) symplectic symmetry of the nuclear many-body problem by working in a basis organized according to this symmetry and truncating the basis by symmetry properties. This seminar presents different basis truncation schemes in the symplectic NCCI framework and their effect on the dimension of the model space and the convergence of calculated observables.

Hosted by Prof. Caprio

*Presented both in person and via zoom. Please email nsladmin@nd.edu for zoom link.*