[Bubble] The 12C(a, g)16O reaction and its implications for stellar helium burning

[Jay Benesch]

https://arxiv.org/abs/1709.03144

86 page RMP article.  Our experiment is discussed on page 36.  I hadn't 
realized how much competition was out there before reading 36-37.

The 12C(a,g)16O reaction and its implications for stellar helium burning
R.J. deBoer, J. Gorres, M. Wiescher, R.E. Azuma, A. Best, C.R. Brune, 
C.E. Fields, S. Jones, M. Pignatari, D. Sayre, K. Smith, F.X. Timmes, E. 
Uberseder
(Submitted on 10 Sep 2017)

     The creation of carbon and oxygen in our universe is one of the 
forefront questions in nuclear astrophysics. The determination of the 
abundance of these elements is key to both our understanding of the 
formation of life on earth and to the life cycles of stars. While nearly 
all models of different nucleosynthesis environments are affected by the 
production of carbon and oxygen, a key ingredient, the precise 
determination of the reaction rate of 12C(a,g)16O, has long remained 
elusive. This is owed to the reaction's inaccessibility, both 
experimentally and theoretically. Nuclear theory has struggled to 
calculate this reaction rate because the cross section is produced 
through different underlying nuclear mechanisms. Isospin selection rules 
suppress the E1 component of the ground state cross section, creating a 
unique situation where the E1 and E2 contributions are of nearly equal 
amplitudes. Experimentally there have also been great challenges. 
Measurements have been pushed to the limits of state of the art 
techniques, often developed for just these measurements. The data have 
been plagued by uncharacterized uncertainties, often the result of the 
novel measurement techniques, that have made the different results 
challenging to reconcile. However, the situation has markedly improved 
in recent years, and the desired level of uncertainty, about 10%, may be 
in sight. In this review the current understanding of this critical 
reaction is summarized. The emphasis is placed primarily on the 
experimental work and interpretation of the reaction data, but 
discussions of the theory and astrophysics are also pursued. The main 
goal is to summarize and clarify the current understanding of the 
reaction and then point the way forward to an improved determination of 
the reaction rate.