Cascade transitions versus cascade transitions in ¹⁵N(p,γ)¹⁶O at the stellar energy range

The reaction ¹⁵N(p,γ)¹⁶O is a branch point in the CNO cycle. Consideration of broad resonances J^π=1^-, 2^-,3^- in ¹⁶O are key points for description of the S-factor and reaction rate for radiative p¹⁵N capture at the stellar energy T₉<10. We report results for astrophysical low-energy S−factor that includes contributions of the ³S₁ resonances due to the E1 transitions and the contribution of M1 transition via ³P₁ scattering wave in p + ¹⁵N channel [1]. The extrapolated S(0) turned out to be within 34.7 − 40.4 keV·b depending on an asymptotic constant. We estimate the contribution of cascade transitions to the reaction rate based on the exclusive experimental data for the cascade transitions ¹⁵N(p,γ_(6.050))¹⁶O, ¹⁵N(p,γ_(6.130))¹⁶O, ¹⁵N(p,γ_(7.117))¹⁶O. The reaction rate enhancement due to these cascade transitions is observed from T₉ > 0.3 and reaches the maximum factor ∼ 1.3 at 1.3T₉. Our results obtained based on the experimental partial S-factors contradict to a peculiar enhancement behavior of the ratio reported in NACRE II at 0.4< T₉ < 10. The latter calls for a careful theoretical investigation of contributions two interfering resonances 2^- at 12.530 MeV and 12.9686 MeV and two interfering resonances 3^- at 13.142 MeV and 13.265 MeV.

1. S. B. Dubovichenko, N. A. Burkova, R. Ya. Kezerashvili, A. S. Tkachenko, B. M. Yeleusheva, arXiv:2303.14680v2, 2023.
   
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