Multibody Photoproduction between 2 and 16 GeV

The SLAC 2.2-m streamer chamber has been used to study photoproduction from hydrogen with a 16-GeV bremsstrahlung beam. The use of a single-hadron trigger permitted a study from 2 to 16 GeV which included photoproduction of the ${\Delta }^{++}$ and of the vector mesons $\rho$, $\omega$, and $\phi$. The sample reported here represents 87 000 pictures containing 7055 hadronic events of which about 2500 were above 5 GeV. Interesting aspects of the data are the dominance of ${\rho }^0$ production in the three-prong topology at high energies, the diffraction character of high-energy ${\rho }^0$ production, the clear indication of the transversality of the ${\rho }^0$ spin orientation, and the apparent interference between the resonant ${\pi }^{+}{\pi }^{-}$ (${\rho }^0$) production and a nonresonant background. Tests of the vector-dominance model are described, including a comparison of total photo-production cross sections derived from our data with those obtained elsewhere by direct measurements.