Pion inelastic scattering to the low-lying excited states ofLi6

The excitation function for ${\pi }^{+}$ inelastic scattering to the $0^{+}$, $T=1\mathrm{}$, 3.563-MeV level of ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$ has been measured at a constant momentum transfer $q\simeq 109$ MeV/c for incident pion energies from 100 to 260 MeV. Although the differential cross sections extracted for the natural-parity transitions to the $3^{+}$, $T=0\mathrm{}$, 2.185-MeV and $2^{+}$, $T=0\mathrm{}$, 4.25-MeV levels are well reproduced within the framework of the distorted-wave impulse approximation, distorted-wave impulse approximation calculations fail to reproduce the anomalous excitation function observed for the transition to the 3.563-MeV level. The shape of the 3.563-MeV excitation function is similar to that previously observed for ${\pi }^{\pm }$ inelastic scattering to the $1^{+}$, $T=1\mathrm{}$, 15.11-MeV state of ${}_{}{}^{12}{}_{}{}^{}\mathrm{C}$ [C. L. Morris et al., Phys. Lett. 108B, 172 (1982)]. The same mechanism may be responsible for the observed excitation functions of both $\Delta S=\Delta T=1\mathrm{}$ transitions. A possible mechanism is the previously proposed direct excitation of $\Delta$-particle-nucleon-hole ($\Delta -h$) components in the wave functions.