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arXiv · 1505.02422

Ab initio calculation of the $np \to d γ$ radiative capture process

Silas R. Beane·Emmanuel Chang·William Detmold·Kostas Orginos·Assumpta Parreño·Martin J. Savage·Brian C. Tiburzi
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Abstract

Lattice QCD calculations of two-nucleon systems are used to isolate the short-distance two-body electromagnetic contributions to the radiative capture process $np \to dγ$, and the photo-disintegration processes $γ^{(\ast)} d \to np$. In nuclear potential models, such contributions are described by phenomenological meson-exchange currents, while in the present work, they are determined directly from the quark and gluon interactions of QCD. Calculations of neutron-proton energy levels in multiple background magnetic fields are performed at two values of the quark masses, corresponding to pion masses of $m_π\sim 450$ and 806 MeV, and are combined with pionless nuclear effective field theory to determine these low-energy inelastic processes. Extrapolating to the physical pion mass, a cross section of $σ^{lqcd}(np\to dγ)=332.4({\tiny \begin{array}{l}+5.4 \\ - 4.7\end{array}})\ mb$ is obtained at an incident neutron speed of $v=2,200\ m/s$, consistent with the experimental value of $σ^{expt}(np \to dγ) = 334.2(0.5)\ mb$.

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Silas R. Beane, Emmanuel Chang, William Detmold, Kostas Orginos, Assumpta Parreño, Martin J. Savage, Brian C. Tiburzi. 2015-05-10. Ab initio calculation of the $np \to d γ$ radiative capture process. https://doi.org/10.1103/physrevlett.115.132001

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