EUROPEAN ORGANIZATION FOR NUCLEAR RESEARCH CERN-PPE/95-xx SEARCH FOR A NEW LIGHT GAUGE BOSON IN DECAYS

Upper limits for the production of new light gauge bosons in 0 , and 0 decays have been obtained with the Crystal Barrel detector. The kinematically well-constrained reactions pp ! 0 0 P have been studied, where P 0 ; ; 0 decays through the emission of a single photon recoiling against a missing state X. X can be a long-lived weakly interacting particle or X !. This paper gives full detail of the analysis of our previous work and extends the search to 0 decay. No signal has been observed and branching ratio upper limits (90 % C:L:) of 6 10 ?5 have been obtained for masses of the gauge boson lying between 65 MeV and 125 MeV (0 decay), 6 10 ?5 , for X masses between 200 MeV and 525 MeV (decay), and 4 10 ?5 , for X masses between 50 MeV and 925 MeV (0 decay). The 0-decay limit represents a factor of 4 to 8 (depending on the X-mass) improvement when compared to the existing limit, whereas the and 0 decay limits have been measured for the rst time, thereby extending the M X range from 125 MeV up to 925 MeV.