Measurement of Spin-Density Matrix Elements for $\phi$-Meson Photoproduction from Protons and Deuterons Near Threshold

Understand

The LEPS/SPring-8 experiment made a comprehensive measurement of the spin-density matrix elements for $\gamma p \to \phi p$, $\gamma d \to \phi p n$ and $\gamma d \to \phi d$ at forward production angles.

• A linearly polarized photon beam at $E_{\gamma}$=1.6-2.4 GeV was used for the production of $\phi$ mesons.
• The natural-parity Pomeron exchange processes remains dominant nearthreshold.
• The unnatural-parity processes of pseudoscalar exchange is visible in the production from nucleons but is greatly reduced in the coherent production from deuterons.