Observation of theE2Nuclear Resonance Effect in Pionic Cadmium

Nuclear resonance effects in mesonic atoms result from near degeneracy of nuclear excitation and atomic de-excitation energies. The $E2\mathrm{}$ nuclear resonance effect was observed in pionic cadmium by comparing selected pionic x-ray intensity ratios from ${}_{}{}^{112}{}_{}{}^{}\mathrm{Cd}$ with those from ${}_{}{}^{111}{}_{}{}^{}\mathrm{Cd}$. The effect for hadronic atoms is now unambiguously established and the results are in close agreement with the theoretical predictions.