Photoproduction on deuterium at 4.3 GeV

Photoproduction of rho0 and ω is studied at 4.3 GeV, using a linearly polarized photon beam in a deuterium bubble chamber. About 4000 rho0 events and 70 coherent ω events are observed. Total and differential cross sections for both coherent and incoherent rho0 production on deuterium are presented, as well as decay angular distributions and density-matrix elements. We find that the t-channel isospin-one exchange amplitude in γN→rho0N is at most 3-10% of the dominant isoscalar amplitude. The rho0 production mechanism is dominantly s-channel helicity-conserving (SHC) on both neutrons and protons. Relative to the SHC amplitudes, the single and double helicity-flip amplitudes at the γrho0 vertex are of the order to 10-15% for t>0.25 GeV2, and have the same sign on both nucleons. This shows that helicty-flip is mainly due to isoscalar exchanges. The ratio of ω to rho0 coherent forward cross sections is found to be 0.16+-0.04. The natural-parity exchange part of γN→ωN is strongly dominated by isoscalar exchanges, and the magnitude of the isovector-exchange is consistent with zero. (author)