Evidence for quark spin-flip in pomeron exchange

Spin-parity analyses of the ωπ system in the reaction γp→(ωπ)p for photon laboratory energies from 20 to 70 GeV have shown that production of the JP=1+b1(1235) meson dominates, with a JP=1− background at the level of 20%. Using vector-meson dominance arguments, this background is shown to be consistent with the data on e+e−→ωπ. The energy dependence of the data imply that the mechanism is a combination of reggeon and pomeron exchange. Assuming that the latter is relevant only for the JP=1− component and extrapolating to W=200 GeV, it is argued that this accounts for most of the preliminary ωπ signal observed by the H1 Collaboration in the same reaction. A residual peak can be ascribed to the b1(1235), which requires a quark spin-flip from pomeron exchange. Precisely the same mechanism occurs in the reaction πp→a1(1260)p.