Spin Density Matrix Elements from diffractive $\varphi$ meson production at HERMES

Exclusive production of $\varphi$ mesons on hydrogen and deuterium targets is studied in the HERMES kinematic region $1<Q^2<7$ GeV${}^2$ and $3.0 < W < 6.3$GeV\mathrm{.}Spindensitymatrixelementsandtheir$Q^{2}$and$t$ dependences are presented. These data are consistent with s-channel helicity conservation in exclusive $\varphi$ meson production. No significant evidence for the contribution of unnatural-parity-exchange amplitudes is found.