Nuclear deformation in the laboratory frame

TL;DR

This paper introduces a new formalism using quantum Monte Carlo methods to analyze nuclear deformation in the laboratory frame, providing a model-independent way to identify deformation signatures in nuclei.

Contribution

It develops a rotationally invariant formalism and computational techniques to extract intrinsic quadrupole parameters without mean-field assumptions.

Findings

Quadrupole distributions serve as model-independent deformation signatures.

The formalism reduces statistical fluctuations in Monte Carlo calculations.

Effective intrinsic quadrupole parameters can be extracted directly from laboratory frame data.

Abstract

We develop a formalism for calculating the distribution of the axial quadrupole operator in the laboratory frame within the rotationally invariant framework of the configuration-interaction shell model. The calculation is carried out using a finite-temperature auxiliary-field quantum Monte Carlo method. We apply this formalism to isotope chains of even-mass samarium and neodymium nuclei, and show that the quadrupole distribution provides a model-independent signature of nuclear deformation. Two technical advances are described that greatly facilitate the calculations. The first is to exploit the rotational invariance of the underlying Hamiltonian to reduce the statistical fluctuations in the Monte Carlo calculations. The second is to determine quadruple invariants from the distribution of the axial quadrupole operator. This allows us to extract effective values of the intrinsic quadrupole shape parameters without invoking an intrinsic frame or a mean-field approximation.