Azimuthal asymmetry in SIDIS off nuclei as probe for $\hat q$
  The energy loss parameter $\hat q$ is one of the fundamental transport parameters of hadronic matter. Using the twist-4 collinear approach, we show that the $\cos \phi$ azimuthal asymmetry in unpolarized semi-inclusive deeply inelastic scattering (SIDIS) off a large nucleus at intermediate transverse momentum is a sensitive observable for its determination. The effect is due to the suppression of the azimuthal asymmetry by final-state multiple scattering. 
Jian-Hua Gao, Andreas Sch\"afer and Jian Zhou
hep-ph