High-Precision Measurement of D(γ,n)p Photodisintegration Reaction and Implications for Big Bang Nucleosynthesis

We report on a high-precision measurement of the D(γ,n)p photodisintegration reaction at the newly commissioned Shanghai Laser Electron Gamma Source, employing a quasimonochromatic γ-ray beam from Laser Compton Scattering. The cross sections were determined over E_{γ}=2.327-7.089  MeV, achieving up to a factor of 2.2 improvement in precision near the neutron separation threshold. Combined with previous data in a global Markov chain Monte Carlo analysis using dibaryon effective field theory, we obtained the unprecedentedly precise p(n,γ)D cross sections and thermonuclear rate, with a precision up to ≈4 times higher than previous evaluations. Implemented in a standard Big Bang nucleosynthesis framework, this new rate decreases uncertainty of the key cosmological parameter of baryon density Ω_{b}h^{2} by up to ≈16% relative to the Laboratory for Underground Nuclear Astrophysics (LUNA) result. A residual ≈1.2σ tension between Ω_{b}h^{2} constrained from primordial D/H observations and cosmic microwave background measurements persists, highlighting the need for improved dd reaction rates and offering potential hints of new physics beyond the standard model of cosmology.