Multipole strength in 12C from the (e,e' alpha ) reaction for momentum transfers up to 0.61 fm-1.

Abstract

We have excited the giant resonance region in $^{12}\mathrm{C}$ via inelastic electron scattering, and have measured the first complete angular correlations for charged particle emission for this reaction for four values of momentum transfer ranging from 0.24 ${\mathrm{fm}}^{\mathrm{\ensuremath{-}}1}$ to 0.61 ${\mathrm{fm}}^{\mathrm{\ensuremath{-}}1}$. By analyzing the \ensuremath{\alpha}-emission channels via the Legendre and resonance formalisms, we unambiguously determined the multipole contributions to the total cross section for \ensuremath{\alpha} emission to the ground state of $^{8}\mathrm{Be}$, and have set limits on these contributions for \ensuremath{\alpha} emission to the first excited state of $^{8}\mathrm{Be}$. We have found that, in both cases, E2 radiation is the strongest contribution but that E0 and E3 contributions cannot be ignored. By constructing total multipole form factors and fitting them within the distorted wave Born approximation using a transition charge density specified by the Tassie model, we deduced multipole transition strengths and fractions of the appropriate sum rules. Our results are compared with those from the (p,p'\ensuremath{\alpha}) and (\ensuremath{\alpha},\ensuremath{\alpha}',\ensuremath{\alpha}) reactions.