Vector meson photoproduction studied in its radiative decay channel

We provide an analysis of vector meson photoproduction in the channel of the vector meson decaying into a pseudoscalar meson plus a photon (i.e., $V\to P\gamma$). It is shown that nontrivial kinematic correlations arise from the measurement of the $P\gamma$ angular distributions in the overall c.m. system in comparison with those in the vector meson rest frame. The implication of such kinematic correlations in the measurement of polarization observables is discussed in terms of the vector meson density matrix elements. For ω meson production, because of its relatively large branching ratios for $\omega \to {\pi }^0\gamma$, additional events from this channel may enrich the information about the reaction mechanism and improve the statistics of the recent measurement of polarized beam asymmetries by the GRAAL Collaboration. For $\varphi \to \eta \gamma ,\rho \to \pi \gamma$, and $K^{*}\to K\gamma$, we expect that additional information about the spin structure of the vector meson production vertex can be derived.

Figure 1

Kinematics for $\gamma N_i\to V{N}_f$ in the overall c.m. system.

Figure 2

Kinematics for $V\to P\gamma$ in the overall c.m. system where the vector meson has momentum $q$. The angle ${\theta }_c$ denotes the decay direction of the photon; θ is the angle between $q$ and the momentum difference between the photon and pseudoscalar meson.