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We evaluate two dominant nuclear reaction rates and their uncertainties thataffect 44Ti production in explosive nucleosynthesis. Experimentally we developthick-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, wealso performed an activation measurement that agrees with the thick targetresult. From the measured yields a stellar reaction rate was developed that issmaller than current statistical-model calculations and recent experimentalresults, which would suggest lower 44Ti production in scenarios for thealpha-rich freeze out. Special attention has been paid to assessing realisticuncertainties of stellar rates produced from a combination of experimental andtheoretical cross sections, which we use to develop a re-evaluation of the44Ti(alpha,p)47V reaction rate. Using these we carry out a sensitivity surveyof 44Ti synthesis in eight expansions representing peak temperature and densityconditions drawn from a suite of recent supernova explosion models. Our resultssuggest that the current uncertainty in these two reaction rates could lead toas large an uncertainty in 44Ti synthesis as that produced by differenttreatments of stellar physics.

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