Transverse $\rho$ asymmetries

The measurement of the transverse target spin asymmetry $A^{sin(\phi −\phi_{S})}_{UT}$ for exclusive production of $\rho^{0}$ mesons at the COMPASS experiment is discussed. The measurement of the asymmetry is done both for the protons and the deuterons. The asymmetry gives an access to the Generalized Parton Distribution function $E$, which is sensitive to the orbital angular momentum of quarks in the nucleon. The measured asymmetry is compatible with zero in the kinematic range: 1 $< Q^{2} <$ 12 (GeV$/c$)$^{2}$, 0.003 $< x_{Bj} <$ 0.35 and 0.05 $< p^{2}_{t} <$ 0.5 (GeV$/c$)$^{2}$ for protons or 0.01 $< p^{2}_{t} <$ 0.5 (GeV$/c$)$^{2}$ for deuterons.