Observation of Substantialp-Wave Capture Strength in theLi7(p→,γ)8BeReaction forEp=80−0keV and Implications for AstrophysicalSFactors

The ${}_{}{}^7{}_{}{}^{}\mathrm{Li}{(\overrightarrow{p},\gamma )}^8\mathrm{Be}$ reaction has been studied using polarized protons having an incident energy in the range $E_p\left(\mathrm{lab}\right)=80-0\mathrm{}$ keV. The measured angular distributions of the cross section $\frac{\sigma \left(\theta \right)}{A_0}$ and analyzing power $A_y\left(\theta \right)$ were interpreted using a model independent transition-matrix element analysis. The large (Å40%) analyzing power at 90° indicates the presence of an appreciable $p$-wave capture strength at these energies. The direct-capture model is used to show that this could reduce the astrophysical $S$ factor by as much as 40%.