Radiative Capture Study by Combining EFT with ab initio Calculations: 7Li(n, y)8Li and 7Be(p, y)8B
- Xilin Zhang, Ohio University
Tuesday, February 25, 11:00 AM - Theory Seminar
NSCL Lecture Hall
The (isospin-mirror) radiative nucleon captures, 7Li(n, γ)8Li and 7Be(p, γ)8B, are subjects of long-standing interest for astrophysics. In this talk, I combine ab initio quantum-Monte-Carlo (QMC) calculations with the Halo-Effective-Field-Theory (Halo-EFT) framework to study them in the low-energy region. The 8Li (8B) nucleus is considered as a shallow neutron+7Li core and neutron+7Li*_(proton+7Be core and proton+7Be*) p-wave bound state. 7Li*_and 7Be* are the core excitations. The scattering and bound states can be studied in Halo-EFT, in which both core and nucleon are treated as fundamental degrees of freedom. The couplings in the EFT Lagrangian are not known a priori and are difficult to extract from experiment. They can, however, be obtained from QMC calculations of the 8Li and 8B nuclei. In our leading order calculation, we use asymptotic normalization coefficients from QMC calculations to fix the parameters in our EFT Lagrangian, which we then apply to study radiative capture reactions. This reduces the need to employ numerically intensive QMC methods to directly compute radiative capture separately at each reaction energy, while still incorporating the ab initio information on nuclear dynamics that these methods provide in the calculation. Our results for both captures compare favorably with available data on total cross sections and branching ratios, within the estimated theoretical uncertainty. I will emphasize the important role of proton-7Be scattering parameters in determining the energy dependence of the cross section (S factor), and demonstrate that their present uncertainties significantly limit attempts to extrapolate data to stellar energies.
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