Reaction rate sensitivity of 44Ti production in massive stars and implications of a thick target yield measurement of 40Ca(alpha,gamma)44Ti

TL;DR

This study measures and evaluates key nuclear reaction rates affecting 44Ti production in supernovae, highlighting significant uncertainties that influence nucleosynthesis predictions and emphasizing the need for precise experimental data.

Contribution

The paper provides new experimental thick-target yield measurements for the 40Ca(alpha,gamma)44Ti reaction and re-evaluates the reaction rates, impacting supernova nucleosynthesis models.

Findings

Measured yields at multiple energies agree with activation results.

Re-evaluated reaction rates are lower than previous models.

Uncertainties in reaction rates significantly affect 44Ti yield predictions.

Abstract

We evaluate two dominant nuclear reaction rates and their uncertainties that affect 44Ti production in explosive nucleosynthesis. Experimentally we develop thick-target yields for the 40Ca(alpha,gamma)44Ti reaction at E(alpha) = 4.13, 4.54, and 5.36 MeV using gamma-ray spectroscopy. At the highest beam energy, we also performed an activation measurement that agrees with the thick target result. From the measured yields a stellar reaction rate was developed that is smaller than current statistical-model calculations and recent experimental results, which would suggest lower 44Ti production in scenarios for the alpha-rich freeze out. Special attention has been paid to assessing realistic uncertainties of stellar rates produced from a combination of experimental and theoretical cross sections, which we use to develop a re-evaluation of the 44Ti(alpha,p)47V reaction rate. Using these we carry out a sensitivity survey of 44Ti synthesis in eight expansions representing peak temperature and density conditions drawn from a suite of recent supernova explosion models. Our results suggest that the current uncertainty in these two reaction rates could lead to as large an uncertainty in 44Ti synthesis as that produced by different treatments of stellar physics.