A search has been carried out for $S=+1\mathrm{}$ baryon states ($Z$ particles) in photoproduction on hydrogen with a missing-mass spectrometer by analyzing the structure in the $K^{-}$ yield as a function of end-point bremsstrahlung energy for fixed laboratory production angles and momentum. Data were taken at the three laboratory angles ${\theta }_K=10\mathrm{}°, 15°, \mathrm{and} 20°$ to check the predictable kinematic behavior of two-body final-state reactions. The synchrotron energy was varied from 3.5 to 6.0 BeV, which corresponds to a missing-mass range of 1.6-2.5 BeV for a laboratory momentum of 2.5 BeV/c. A fit to the excitation function at ${\theta }_K=10\mathrm{}°$ suggests structure in addition to a smooth background, while the ${\theta }_K=15\mathrm{}°$ data can be adequately fitted with a smooth background alone. Upper limits for photoproduction cross sections for each $S=+1\mathrm{}$ state at ${\theta }_K=10\mathrm{}° \mathrm{and} 15°$ are, respectively, 20 and 4 nb/sr in the center-of-mass system.

• Received 26 March 1969

DOI:https://doi.org/10.1103/PhysRev.185.1687