Search forpwaves in low-energy proton capture reactions relevant to the solar neutrino problem

A previous study of the ground-state transition of the ${}_{}{}^7{}_{}{}^{}\mathrm{Li}(\overrightarrow{p}, \gamma ){}_{}{}^8{}_{}{}^{}\mathrm{Be}$ reaction at energies of $E_p\left(\mathrm{lab}\right)=80-0\mathrm{}$ keV indicated the possibility of a large $p$-wave capture amplitude in this reaction. A similar $p$-wave component in the ${}_{}{}^7{}_{}{}^{}\mathrm{Be}(p, \gamma ){}_{}{}^8{}_{}{}^{}\mathrm{B}$ reaction could seriously affect the extrapolation used to obtain the astrophysical $S$ factor. The present work examines this possibility by observing the closely related ${}_{}{}^7{}_{}{}^{}\mathrm{Li}(\overrightarrow{p}, {\gamma }_{16.6}){}_{}{}^8{}_{}{}^{}\mathrm{Be}_{}^{*}{}_{}{}^{}$ ($2^{+}$, $T=0+1)$ reaction with polarized protons at and below 80 keV. Experimental data for $\frac{\sigma \left(\theta \right)}{A_0}$ and $A_y\left(\theta \right)$ for capture to the third (16.6 MeV) excited state of 8Be are presented, and the implications discussed.