Developing new methods to investigate nuclear physics input to the cosmological lithium problem

K.J Cook,I.P Carter,D.H Luong,D.J Hinde,E Williams,M Dasgupta,K Ramachandran,C Simenel,A Wallner,M Srncik,T Kibédi,D Huy Luong,M Reed,M Evers

doi:10.1051/epjconf/20136303011

Abstract

A significant challenge to nuclear astrophysics is the cosmological lithium problem, where models of Big Bang nucleosynthesis indicate abundances of 7 Li two to four times larger than what is inferred via spec- troscopic measurements of metal-poor stars. Recent experimental techniques developed for nuclear reaction studies at energies near the fusion barrier, if extended to reactions of astrophysical interest, may help under- stand nuclear reactions that can affect the production of 7 Li during the Big Bang. Experiments at the ANU, using new experimental techniques, have provided complete pictures of the breakup mechanisms of light nuclei in collisions with heavy targets, such as 208 Pb and 209 Bi (1). These experiments revealed dominant breakup mechanisms which had not even been considered in theoretical models. The study of the breakup of 6 Li and 7 Li following interactions with 58,64 Ni and 27 Al acts as a stepping stone from this previous work towards future ex- perimental studies of breakup reactions of astrophysical relevance. In all cases studied, breakup is dominantly triggered by nucleon transfer between the colliding partners, but the transfer mechanisms are different. The findings of these experiments and experimental considerations for extensions to reactions of light nuclei, such as d + 7 Be, will be presented.

Highlights

There is a significant discrepancy between the abundance of 7Li observed in metal-poor halo stars and that predicted by Big Bang Nucleosynthesis (BBN) calculations
On the order of 3-4 times more 7Li is predicted to be present in the primordial universe than is inferred via observation. This disagreement, known as the primordial lithium problem, has posed a significant challenge to astrophysics since its discovery in 1982 [2]. Possible solutions to this discrepancy have come from many areas of physics: i) investigating stellar models [3, 4], ii) improved observations of lithium in metal-poor stars [5], iii) low metallicity gases in the Small Magellanic Cloud [6], iv) non-standard cosmologies and physics beyond the standard model [7,8,9,10,11], and v) nuclear physics input into models
The 7Be(d,p)2α reaction has been shown in a sensitivity study [17] to be able to resolve the primordial lithium problem if the reaction rate was a factor of 100 times larger at low energies than the previous estimate, which assumed a constant S -factor [18]

Summary

The 7Li problem

There is a significant discrepancy between the abundance of 7Li observed in metal-poor halo stars and that predicted by Big Bang Nucleosynthesis (BBN) calculations. On the order of 3-4 times more 7Li is predicted to be present in the primordial universe than is inferred via observation This disagreement, known as the primordial lithium problem, has posed a significant challenge to astrophysics since its discovery in 1982 [2]. Possible solutions to this discrepancy have come from many areas of physics: i) investigating stellar models [3, 4], ii) improved observations of lithium in metal-poor stars [5], iii) low metallicity gases in the Small Magellanic Cloud [6], iv) non-standard cosmologies and physics beyond the standard model [7,8,9,10,11], and v) nuclear physics input into models. A new detector array at the Australian National University (ANU), designed to study the breakup of light nuclei, enables coincident measurements of light charged particles and will allow this re-examination to take place

The ANU BALIN array

Pictures of breakup mechanisms of 7Li reacting with 58Ni

Pictures of breakup mechanisms of 7Li reacting with 27Al

Conclusions