Odd-even staggerings on nuclear binding energy described by the covariant density functional theory

TL;DR

This study systematically analyzes odd-even staggering in nuclear binding energies using covariant density functional theories, highlighting discrepancies and improvements with modified pairing interactions, and emphasizing the need for a unified relativistic mechanism.

Contribution

It demonstrates the application of covariant density functional theories to describe OES in various isotopes and proposes modifications to pairing interactions for better accuracy.

Findings

CDF models describe OES reasonably well for many isotopes.

Discrepancies in light and heavy isotopes are partially corrected by Z- or N-dependent factors.

Unified relativistic mechanisms are needed for improved quantitative accuracy.

Abstract

The odd-even staggerings (OES) on nuclear binding energies are studied systematically within the covariant density functional (CDF) theories, specifically the relativistic Hartree-Fock-Bogoliubov (RHFB) and the relativistic Hartree-Bogoliubov (RHB) theories. Taking the finite-range Gogny force D1S as an effective pairing interaction, both CDF models can provide appropriate descriptions on the OESs of nuclear binding energies for C, O, Ca, Ni, Zr, Sn, Ce, Gd and Pb isotopes as well as for N=50 and 82 isotones. However, due to the inconsistence between the non-relativistic pairing interaction and the relativistic effective Lagrangians, there exist some systematical discrepancies from the data, i.e., the underestimated OESs in light C and O isotopes and the overestimated ones in heavy region, respectively. Such discrepancies can be eliminated partially by introducing a $Z$- or $N$-dependent strength factor into the pairing force Gogny D1S. In addition, successful descriptions of the occupation numbers of Sn isotopes are achieved with the optimized Gogny pairing force. Furthermore, the analysis of the systematics of both pairing effects and nuclear binding energy indicate the requirement of an unified relativistic mechanism in both p-p and p-h channels to improve the quantitative precision of the theory.