Precision measurements of ²H(d,p)³H and ²H(d,n)³He total cross sections at Big Bang nucleosynthesis energies

Recent Wilkinson Microwave Anisotropy Probe (WMAP) measurements have determined the baryon density of the Universe _b with a precision of about 4%. With _b tightly constrained, comparisons of Big Bang nucleosynthesis (BBN) abundance predictions to primordial abundance observations can be made and used to test BBN models and/or to further constrain abundances of isotopes with weak observational limits. To push the limits and improve constraints on BBN models, uncertainties in key nuclear reaction rates must be minimized. To this end, we made new precise measurements of the ²H(d,p)³H and ²H(d,n)³He total cross sections at lab energies from 110 to 650 keV. A complete fit was performed in energy and angle to both angular distribution and normalization data for both reactions simultaneously. By including parameters for experimental variables in the fit, error correlations between detectors, reactions, and reaction energies were accurately tabulated by computational methods. With uncertainties around 2%±1% scale error, these new measurements significantly improve on the existing data set. At relevant temperatures, by using the data of the present work, both reaction rates are found to be about 7% higher than those in the widely used NACRE (nuclear astrophysics compilation of reaction rates) database. These data will thus lead not only to reduced uncertainties, but also to modifications in the BBN abundance predictions.

©2006 The American Physical Society