# Neutron drip line in the Ca region from Bayesian model averaging

## TL;DR

This paper uses Bayesian model averaging and machine learning to predict the neutron drip line in calcium isotopes, providing quantified certainty levels and consistent predictions across models.

## Contribution

It introduces a Bayesian approach with Gaussian processes to assess the bound nature of neutron-rich nuclei, improving predictions of the calcium drip line with uncertainty quantification.

## Key findings

- $^{68}$Ca has a 76% probability to be bound to two-neutron emission.
- $^{61}$Ca likely decays by neutron emission with 46% probability.
- Predictions are consistent across different global mass models despite raw prediction variations.

## Abstract

The region of heavy calcium isotopes forms the frontier of experimental and theoretical nuclear structure research where the basic concepts of nuclear physics are put to stringent test. The recent discovery of the extremely neutron-rich nuclei around $^{60}$Ca [Tarasov, 2018] and the experimental determination of masses for $^{55-57}$Ca (Michimasa, 2018] provide unique information about the binding energy surface in this region. To assess the impact of these experimental discoveries on the nuclear landscape's extent, we use global mass models and statistical machine learning to make predictions, with quantified levels of certainty, for bound nuclides between Si and Ti. Using a Bayesian model averaging analysis based on Gaussian-process-based extrapolations we introduce the posterior probability $p_{ex}$ for each nucleus to be bound to neutron emission. We find that extrapolations for drip-line locations, at which the nuclear binding ends, are consistent across the global mass models used, in spite of significant variations between their raw predictions. In particular, considering the current experimental information and current global mass models, we predict that $^{68}$Ca has an average posterior probability ${p_{ex}\approx76}$% to be bound to two-neutron emission while the nucleus $^{61}$Ca is likely to decay by emitting a neutron (${p_{ex}\approx 46}$ %).