Search for rare and forbidden eta ' decays

We have searched for rare and forbidden decays of the {eta}{sup '} meson in hadronic events at the CLEO II detector. The search is conducted on 4.80 fb{sup -1} of e{sup +}e{sup -} collisions at 10.6 GeV center-of-mass energy at the Cornell Electron Storage Ring. We find no signals, and set 90% confidence level upper limits of their branching fractions: B({eta}{sup '}{yields}e{sup +}e{sup -} {eta})<2.4x10{sup -3} , B({eta}{sup '}{yields}e{sup +}e{sup -} {pi}{sup 0})<1.4x10{sup -3} , B({eta}{sup '}{yields}e{sup +}e{sup -} {gamma})<0.9x10{sup -3} , and B({eta}{sup '}{yields}e{mu})<4 .7x10{sup -4} . We also fit the matrix element of the {eta}{sup '}{yields}{pi}{sup +}{pi}{sup -}{eta} Dalitz plot with the parametrization |M|{sup 2}=A|1+{alpha}y|{sup 2} , where y is a linear function of the kinetic energy of the {eta} , and find Re({alpha})=-0.021{+-}0.025 . (c) 1999 The American Physical Society.