Diffractive $\rho^{0}$ production at COMPASS

Diffractive leptoproduction of $\rho^{0}$ mesons, $\mu + N\rightarrow\mu + N + \rho$ is measured at COMPASS at $< W > =$ 10 GeV over a wide range of Q$^{2}$, 0.01 $< Q^{2} <$ 10 GeV$^{2}$. Angular distributions to determine spin density matrix elements and longitudinal double-spin asymmetry $A^{\rho}_{1}$ are investigated. Preliminary results are presented. They are consistent with a substantial increase of $R =\sigma_{L} /\sigma_{T}$ with $Q^{2}$, a weak violation of SCHC. The asymmetry is consistent with zero in the whole kinematical range.