Ab initio Calculation of the np→dγ Radiative Capture Process

Area of Science:

• Nuclear Physics
• Quantum Chromodynamics (QCD)

Background:

• Two-nucleon systems and their electromagnetic interactions are crucial for understanding nuclear forces.
• Current models often use phenomenological meson-exchange currents for short-distance electromagnetic contributions.

Purpose of the Study:

• To isolate and calculate short-distance two-body electromagnetic contributions in np→dγ and γ^{(*)}d→np processes.
• To determine these contributions directly from QCD, bypassing phenomenological models.

Main Methods:

• Utilizing Lattice QCD to calculate neutron-proton energy levels in magnetic fields.
• Employing two different quark masses (pion masses ~450 and 806 MeV).
• Combining Lattice QCD results with pionless nuclear effective field theory.

Main Results:

• A cross section of ~17 mb was obtained at m_{π}~806 MeV using only Lattice QCD inputs.
• Extrapolation to the physical pion mass yielded a cross section of σ^{lqcd}(np→dγ)=334.9(+5.2-5.4) mb.
• The calculated cross section is consistent with the experimental value of σ^{expt}(np→dγ)=334.2(0.5) mb.

Conclusions:

• Lattice QCD provides a direct, fundamental method to calculate electromagnetic contributions in nuclear reactions.
• The study validates the use of QCD-derived interactions for nuclear processes.
• Results align with experimental measurements, supporting the accuracy of the Lattice QCD approach.