SEARCH FOR NEW GAUGE BOSONS IN THE RADIATIVE DECAY Z-]GAMMA-X

We consider the decay Z --> gamma-X where X is a new gauge boson corresponding to an extra U'(1) gauge group factor and find that its partial width can be as large as 5% (the experimental limit for the width of a new decay mode), providing the limit for the X-boson coupling constant: alpha'X less than or similar to 0.1 M(X)/1 GeV)2