Abstract
The reaction $^{6}\mathrm{Li}$($\ensuremath{\gamma},{\ensuremath{\pi}}^{+})$$^{6}\mathrm{He}$ was studied over the angular range ${\ensuremath{\theta}}_{\ensuremath{\pi}}=40$--150$\ifmmode^\circ\else\textdegree\fi{}$ with the aim of investigating the halo structure of $^{6}\mathrm{He}$. Photons from a bremsstrahlung beam were tagged in the energy range ${E}_{\ensuremath{\gamma}}=170$--220 MeV at a resolution of $\ensuremath{\Delta}{E}_{\ensuremath{\gamma}}=630$ keV, and positively charged pions detected using high resolution stacked HpGe detectors. The measured angular distributions for the resolved $^{6}\mathrm{He}$ ground and 1.80 MeV excited states are compared to previous measurements and theoretical calculations based on the impulse approximation. It is deduced that the ground state rms radius of the $^{6}\mathrm{He}$ nucleus may be larger than previously thought and that the first excited 1.80 MeV state may also be a halo state.
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