Phase Shifts forp−He4Elastic Scattering Between 20 and 40 MeV

A phase-shift analysis of recent $p-{}_{}{}^4{}_{}{}^{}\mathrm{He}$ cross-section and polarization data has been performed between 20 and 40 MeV proton laboratory energy. A set of single-energy results is presented, which shows little scatter as a function of energy. The match between our results and existing phase-shift sets below 20 and above 40 MeV is excellent. The most striking feature of the phase shifts above the inelastic threshold at 23.02 MeV is the dominance of absorption in the even partial waves. There is weak evidence in the energy dependence of the phase shifts for levels of ${}_{}{}^5{}_{}{}^{}\mathrm{Li}$ other than the well-known ${\frac{3}{2}}^{+}$ second excited state. Tentative assignments of spin and parity of such levels are discussed. An $R$-matrix parametrization of the ${}_{}{}^2{}_{}{}^{}D_{\frac{3}{2}}^{}{}_{}{}^{}$ phase shift has been performed over the $p-{}_{}{}^4{}_{}{}^{}\mathrm{He}$ resonance corresponding to the second excited state of ${}_{}{}^5{}_{}{}^{}\mathrm{Li}$, and improved level parameters are presented for this state.