Search For A New Light Gauge Boson In Pi(0), Eta And Eta' Decays

Upper limits for the production of new light gauge bosons in pi(0), eta and eta' decays have been obtained with the Crystal Barrel detector. The kinematically well-constrained reactions <(p)over bar p> --> eta(0) eta(0) P have been studied, where P = eta(0), eta eta' decays through the emission of a single photon recoiling against a missing state X. X can be a long-lived weakly interacting particle or it decays into . The resulting branching ratio upper limits (90% C.L.) are: 6 x 10(-5) for masses M(X) of the missing particle X lying between 65 MeV/c(2) and 125 MeV/c(2) (pi(0) decay), 6 x 10(-5) for M(X) between 200 MeV/c(2) and 525 MeV/c(2) (eta decay), and 4 x 10(-5) for M(X) between 50 MeV/c(2) and 925 MeV/c(2) (eta/decay). The eta(0)-decay limit represents an improvement by a factor of 4 to 8 (depending on M(X)) when compared to the existing limit, whereas the eta and eta' decay limits have been measured the first time, thereby extending the M(X) range from 125MeV/c(2) up to 925 MeV/c(2).