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00925njm 22002777a 4500 dc Beane, Silas R. author Chang, Emmanuel author Detmold, William author Orginos, Kostas author Parreño García, Assumpta author Savage, Martin J. author Tiburzi, Brian C. author NPLQCD Collaboration author 2019-05-08T15:20:06Z 2019-05-08T15:20:06Z 2015-09-24 2019-05-08T15:20:07Z Lattice QCD calculations of two-nucleon systems are used to isolate the short-distance two-body electromagnetic contributions to the radiative capture process n p → d γ , and the photo-disintegration processes γ ( * ) d → n p . 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 ∼ 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 π ∼ 806     MeV , using only lattice QCD inputs, a cross section σ 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 lqcd ( n p → d γ ) = 334.9 ( + 5.2 − 5.4 )     mb is obtained at the same incident neutron speed, consistent with the experimental value of σ expt ( n p → d γ ) = 334.2 ( 0.5 )     mb . Física de partícules Experiments Particle physics Experiments Ab initio Calculation of the np→dγ Radiative Capture Process