H2(p,γ)He3 cross section measurement using high-energy-density plasmas

An absolute cross section for the radiative capture reaction $^{2}\mathrm{H}(p,\ensuremath{\gamma})^{3}\mathrm{He}$ has been measured at the OMEGA laser facility using inertially confined plasmas. These high-temperature plasmas are created by imploding a fuel-containing capsule using laser ablation, and are advantageous in that they better mimic astrophysical systems. We measure an $S$ factor for this reaction of $0.429\ifmmode\pm\else\textpm\fi{}0.{026}_{\mathrm{stat}}\ifmmode\pm\else\textpm\fi{}0.{072}_{\mathrm{sys}}$ eV b at ${E}_{c.m.}=16.35\ifmmode\pm\else\textpm\fi{}0.40$ keV, which is higher than the adopted evaluations. This reaction is important as a source of nuclear energy in protostars and brown dwarfs. It is also a critical reaction during big-bang nucleosynthesis, and an accurate cross section can be used as a constraint on cosmology.