The impact of mass uncertainties on the r-process nucleosynthesis in neutron star mergers

TL;DR

This paper investigates how uncertainties in nuclear mass predictions affect r-process nucleosynthesis in neutron star mergers, highlighting the importance of improved nuclear models for accurate element yield predictions.

Contribution

It systematically analyzes both model and parameter uncertainties in nuclear masses and their impact on r-process element synthesis in neutron star mergers.

Findings

Uncorrelated parameter uncertainties cause 20-40% abundance deviations.

Model uncertainties generally exceed parameter uncertainties.

Reducing nuclear mass uncertainties is crucial for accurate r-process predictions.

Abstract

Theoretical predictions of element yields from the rapid neutron capture (r-) process are subject to large uncertainties due to incomplete knowledge of nuclear properties and approximative hydrodynamical modeling of matter ejection. A major source of uncertainty in determining ejecta composition and radioactive decay heat is the lack of nuclear mass data for exotic neutron-rich nuclei produced during neutron irradiation. We examine both model (systematic) and parameter (statistical) uncertainties affecting nuclear mass predictions and their impact on r-process nucleosynthesis, and consequently, the composition of neutron star merger ejecta. To estimate the effect of model uncertainties, we consider five nuclear mass models that accurately describe known masses. We also use a backward-forward Monte Carlo method to estimate uncorrelated uncertainties from local variations in model parameters, constraining them to experimentally known masses before propagating them to unknown masses of neutron-rich nuclei. These mass uncertainties are then applied to a 1.38-1.38 M$_{\odot}$ neutron star merger model, considering a wide range of ejecta trajectories. We find that uncorrelated parameter uncertainties lead to ejected abundance uncertainties of 20% up to A $\simeq$ 130, 40% between A=150 and 200, with peaks around A $\simeq$ 140 and A $\simeq$ 203, leading to deviations of 100-300%. While correlated model uncertainties generally exceed parameter uncertainties for most nuclei, both have a significant impact on heavy element production. Overall, improvements in nuclear models are essential to reducing uncertainties in r-process predictions. Both correlated model uncertainties and coherent determination of parameter uncertainties are crucial for sensitivity analysis in r-process nucleosynthesis.