Ab initio Calculation of the np → dy Radiative Capture Process

• Main Authors: Beane, Silas R. (Author), Chang, Emmanuel (Author), Detmold, William (Contributor), Orginos, Kostas (Author), Parreno, Assumpta (Author), Savage, Martin J. (Author), Tiburzi, Brian C. (Author)
• Other Authors: Massachusetts Institute of Technology. Center for Theoretical Physics (Contributor), Massachusetts Institute of Technology. Department of Physics (Contributor)
• Format: Article
• Language: English
• Published: American Physical Society, 2015-09-28T12:20:28Z.
• Subjects: Article
• Online Access: Get fulltext

 Lattice QCD calculations of two-nucleon systems are used to isolate the short-distance two-body electromagnetic contributions to the radiative capture process np → dγ, and the photo-disintegration processes γ[superscript (*)]d → 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[subscript π] ~ 450 and 806 MeV, and are combined with pionless nuclear effective field theory to determine the amplitudes for these low-energy inelastic processes. At m[subscript π] ~ 806  MeV, using only lattice QCD inputs, a cross section σ[superscript 806  MeV] ~ 17  mb is found at an incident neutron speed of v = 2,200  m/s. Extrapolating the short-distance contribution to the physical pion mass and combining the result with phenomenological scattering information and one-body couplings, a cross section of σ[superscript lqcd](np → dγ) = 334.9([+5.2 over -5.4])  mb is obtained at the same incident neutron speed, consistent with the experimental value of σ[superscript expt](np → dγ) = 334.2(0.5)  mb.