Radii of proton emitters

TL;DR

This paper investigates the charge radii of proton-unbound nuclei using a complex-energy approach, revealing a nonmonotonic dependence on decay energy and a halolike enhancement near the threshold, which aids experimental interpretation.

Contribution

It introduces a novel complex-energy method to define and analyze the radius of proton resonances, bridging theoretical and experimental perspectives.

Findings

Identified an early-time plateau where the resonance radius matches the experimental real-energy radius.

Discovered a nonmonotonic relationship between complex radius and decay energy.

Observed a local increase in charge radius across the decay threshold, resembling a halolike enhancement.

Abstract

Nuclear radius is a fundamental structural observable that informs many properties of atomic nuclei and nuclear matter. Experimental studies of radii in drip line nuclei are in the forefront of research with radioactive ion beams. Of particular interest are charge radii of proton-unbound nuclei that will soon be approached in laser spectroscopy. In this Letter, using the complex-energy approach and direct time propagation, we investigate the radius of the proton resonance whose size is ill defined in the standard stationary quantum-mechanical description. An early-time plateau is identified during which the radius of the Gamow resonance coincides with the real-energy radius accessible experimentally. We demonstrate a nonmonotonic dependence of the complex radius on decay energy and a local increase of the charge radius across the threshold (a halolike enhancement).