Deuterium and lithium for precision cosmology

• Applicants: Professor Dr. Daniel Bemmerer; Professor Dr. Kai Zuber
• Subject Area: Nuclear and Elementary Particle Physics, Quantum Mechanics, Relativity, Fields ; Astrophysics and Astronomy
• Term: from 2017 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 329701419

The aims of the proposed project are:1. Improve the best Big Bang Nucleosynthesis (BBN) observable, to make it competitive to the cosmic microwave background (CMB):The precision of the predicted 2H abundance as a function of the baryon-to-photon ratio shall be improved to approach the precision of the 2H observation. Thus, the precision of the currently most precise BBN tool, 2H, shall be further sharpened so that it becomes competitive in its impact on the baryon-to-photon ratio to the CMB constraint.2. Sharpen the discrepancy for the worst BBN observable, in order to enable it as a tool for new physics:The precision of the predicted 7Li abundance as a function of the baryon-to-photon ratio shall be improved, not in a hope to resolve the cosmic 7Li problem, but instead in order to enable the use of the discrepancy between CMB-predicted and observed 7Li abundances to explore new physics in the first 1000 seconds of the universe.3. Improve the precision of the predicted fluxes of solar 7Be and 8B neutrinos:The precision of the worst-known nuclear input for the solar 7Be neutrino flux shall be improved, in order to enable a precision of better than 5% for the predicted 7Be neutrino flux, and to improve the precision of the predicted 8B neutrino flux.These three aims shall be reached with new cross section measurements on the nuclear reactions dominating the error bars for Big Bang 2H, 2H(p,gamma)3He (aim 1), and for Big Bang 7Li and solar 7Be and 8B neutrinos, 3He(alpha,gamma)7Be (aims 2 and 3).WP 1: At the LUNA 400 kV underground accelerator, the 2H(p,gamma)3He cross section shall be measured with a systematic precision of 3% or better, in 10 keV energy steps from 50-400 keV proton beam energy.WP 2: In Dresden, at the 3 MV Tandetron accelerator the angular distribution of the 3He(alpha,gamma)7Be reaction shall be measured at 1 MeV center-of-mass energy with 2% precision. In addition, the 3He(alpha,gamma)7Be cross section shall be measured by activation, using the new Felsenkeller 150% ultra-low background germanium detector, at eight points in the center-of-mass energy range between 0.25 and 1.1 MeV.

• DFG Programme: Research Grants