The ⁷ Be( <i>d</i> , <i>p</i> )2α Cross Section at Big Bang Energies and the Primordial ⁷ Li Abundance

Abstract

The WMAP satellite, devoted to the observations of the anisotropies of the\nCosmic Microwave Background (CMB) radiation, has recently provided a\ndetermination of the baryonic density of the Universe with unprecedented\nprecision. Using this, Big Bang Nucleosynthesis (BBN) calculations predict a\nprimordial 7Li abundance which is a factor 2-3 higher than that observed in\ngalactic halo dwarf stars. It has been argued that this discrepancy could be\nresolved if the 7Be(d,p)2alpha reaction rate is around a factor of 100 larger\nthan has previously been considered. We have now studied this reaction, for the\nfirst time at energies appropriate to the Big Bang environment, at the CYCLONE\nradioactive beam facility at Louvain-la-Neuve. The cross section was found to\nbe a factor of 10 smaller than derived from earlier measurements. It is\nconcluded therefore that nuclear uncertainties cannot explain the discrepancy\nbetween observed and predicted primordial 7Li abundances, and an alternative\nastrophysical solution must be investigated.\n Comment: To appear in Astrophysical J. Letters