arXiv subjects

Pradeepa Premarathna

Publications and source records attributed to Pradeepa Premarathna.

3 recordsLinked to original sources

arXiv2024

Coupled-channels treatment of $^7\mathrm{Be}(p,γ)^8\mathrm{B}$ in effective field theory

The E1 and M1 contributions to $^7\mathrm{Be}(p,γ)^8\mathrm{B}$ at low energies are calculated in halo effective field theory. The excited $^7\mathrm{Be}^\star$ core is included as an explicit degree of freedom in a coupled-channels calculation. The E1 transition is calculated up to next-to-next-to-leading order. The leading contribution from M1 transition that gives significant contribution in a narrow energy region around the $1^+$ resonance state of $^8$B is included. We compare our results with previous halo effective field theory calculations that also included the $^7\mathrm{Be}^\star$ as an explicit degree of freedom. We disagree with these previous calculations in both the formal expressions and also in the analysis. Bayesian inference of the data gives $S_{17}(0)=21.0(7)$ eV b when combined with the expected theory error.

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arXiv2024

Coupled-channel treatment of $^7\mathrm{Li}(n,γ)^8\mathrm{Li}$ in effective field theory

The E1 contribution to the capture reaction $^7\mathrm{Li}(n,γ)^8\mathrm{Li}$ is calculated at low energies. We employ a coupled-channel formalism to account for the $^7\mathrm{Li}^\star$ excited core contribution. We develop a halo effective field theory power counting where capture in the spin $S=2$ channel is enhanced over the $S=1$ channel. A next-to-leading order calculation is presented where the excited core contribution is shown to affect only the overall normalization of the cross section. The momentum dependence of the capture cross section, as a consequence, is the same in a theory with or without the excited $^7\mathrm{Li}^\star$ degree of freedom at this order of the calculation. The kinematical signature of the $^7\mathrm{Li}^\star$ core is negligible at momenta below 1 MeV and significant only beyond the $3^+$ resonance energy, though still compatible with a next-to-next-to-leading order correction. We compare our formalism with a previous halo effective field theory calculation [Zhang, Nollett, and Phillips, Phys. Rev. C 89, 024613 (2014)] that also treated the $^7\mathrm{Li}^\star$ core as an explicit degree of freedom. Our formal expressions and analysis disagree with this earlier work in several aspects.

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arXiv2019

Bayesian analysis of capture reactions $^3\mathrm{He}(α,γ)^7\mathrm{Be}$ and $^3\mathrm{H}(α,γ)^7\mathrm{Li}$

Bayesian analysis of the radiative capture reactions $^3\mathrm{He}(α,γ)^7\mathrm{Be}$ and $^3\mathrm{H}(α,γ)^7\mathrm{Li}$ are performed to draw inferences about the cross sections at threshold. We do a model comparison of two competing effective field theory power countings for the capture reactions. The two power countings differ in the contribution of two-body electromagnetic currents. In one power counting, two-body currents contribute at leading order, and in the other they contribute at higher orders. The former is favored for $^3\mathrm{He}(α,γ)^7\mathrm{Be}$ if elastic scattering data in the incoming channel is considered in the analysis. Without constraints from elastic scattering data, both the power countings are equally favored. For $^3\mathrm{H}(α,γ)^7\mathrm{Li}$, the first power counting with two-body current contributions at leading order is favored with or without constraints from elastic scattering data.

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