Systematics of 2+ states in C isotopes from the ab initio no-core shell model

TL;DR

This study uses ab initio no-core shell model calculations to analyze low-lying 2+ states in carbon isotopes, comparing results with experimental data and exploring the effects of nuclear interactions without fitting parameters.

Contribution

It provides first-principles calculations of excitation energies and electromagnetic properties of carbon isotopes, highlighting the impact of three-nucleon forces and model space extrapolations.

Findings

Good agreement with experimental trends in excitation energies.

Calculated B(E2) values generally match experimental data, with some discrepancies.

Sensitivity of transition rates to nuclear interaction details, especially in 16C.

Abstract

We study low-lying states of even carbon isotopes in the range A = 10 - 20 within the large- scale no-core shell model (NCSM). Using several accurate nucleon-nucleon (NN) as well as NN plus three-nucleon (NNN) interactions, we calculate excitation energies of the lowest 2+ state, the electromagnetic B(E2; 2+1 -> 0+1) transition rates, the 2+1 quadrupole moments as well as se- lected electromagnetic transitions among other states. Recent experimental campaigns to measure 2+-state lifetimes indicate an interesting evolution of nuclear structure that pose a challenge to reproduce theoretically from first principles. Our calculations do not include any effective charges or other fitting parameters. However, calculated results extrapolated to infinite model spaces are also presented. The model-dependence of those results is discussed. Overall, we find a good agree- ment with the experimentally observed trends, although our extrapolated B(E2; 2+1 -> 0+1) value for 16C is lower compared to the most recent measurements. Relative transition strengths from higher excited states are investigated and the influence of NNN forces is discussed. In particular for 16C we find a remarkable sensitivity of the transition rates from higher excited states to the details of the nuclear interactions.