Decay Modes of the Isoscalar Giant Quadrupole Resonance inNi58

Particle decay modes of the giant quadrupole resonance in ${}_{}{}^{58}{}_{}{}^{}\mathrm{Ni}$ have been determined in a particle-particle angular correlation experiment. The branching ratios are (59±12)% and (12±4)% [(30±6)% and (6±2)% of the isoscalar $E2\mathrm{}$ energy-weighted sum-rule strength] for proton and $\alpha$-particle decay, respectively, and are very similar to those of the underlying continuum and the statistical-model predictions. Our results disagree with a recent electroproduction singles experiment.