REGGE TRAJECTORIES AND PARTICLE SIZE

Two models of rising trajectories are contrasted. The first, based on single-channel rotational excitations, leads to a mean square particle radius which increases linearly with angular momentum for excitations on a trajectory. The second model, which makes use of a conjectured weakly violated selection rule, gives a particle radius which is constant along a trajectory. The approximate selection rule explains the narrowness of the higher resonances. © 1969 The American Physical Society.