Color entanglement for $\gamma$-jet production in polarized pA   collisions
  A more reliable treatment of transverse momentum dependent physics and in particular transverse single spin asymmetries is urgently required, e.g. for polarized pA physics including novel effects like color entanglement. We argue that the measurement of azimuthal angular correlations of photons and jets produced in pA collisions provides a direct access to the novel gluon distribution $G_4$ that enters into many such processes. 
Andreas Sch\"afer and Jian Zhou
hep-ph