Search for the Z+-baryon

A search was made for the production of Z+-baryons of mass 1370 MeV in the reaction π−+p→K−+Z+ at a pion momentum of 2.3 GeV/c, using spark chambers. No evidence for their existence was found. The upper limit to the differential cross-section at zero degrees of the reaction investigated is estimated to be 50 µb/sr, or about 18 times smaller than might be expected on the basis ofSU3 invariance.