Hard Exclusive $\rho^0$-Meson Production at COMPASS.

Heiner Wollny
New results for the transverse target spin azimuthal asymmetry $A_{UT}^{\sin(\phi-\phi_S)}$ for hard exclusive $\rho^0$-meson production on a transversely polarised $^6$LiD and NH$_3$ target will be presented. The measurement was performed with the COMPASS detector using the $160$\,GeV/$c$ muon beam of the SPS at CERN. The asymmetry is sensitive to the nucleon helicity-flip generalised parton distribution $E$, which is related to the orbital angular momentum of quarks in the nucleon.