1. D. Boer et al., Gluons and the quark sea at high energies: Distributions, polarization, tomography, arXiv:1108.1713 [ INSPIRE ].
2. X.-d. Ji, J.-P. Ma and F. Yuan, QCD factorization for spin-dependent cross sections in DIS and Drell-Yan processes at low transverse momentum, Phys. Lett. B 597 (2004) 299 [ hep-ph/0405085 ] [ INSPIRE ].
3. X.-d. Ji, J.-p. Ma and F. Yuan, QCD factorization for semi-inclusive deep-inelastic scattering at low transverse momentum, Phys. Rev. D 71 (2005) 034005 [ hep-ph/0404183 ] [ INSPIRE ].
4. A. Bacchetta, D. Boer, M. Diehl and P.J. Mulders, Matches and mismatches in the descriptions of semi-inclusive processes at low and high transverse momentum, JHEP 08 (2008) 023 [ arXiv:0803.0227 ] [ INSPIRE ].
5. J. Collins, Foundations of perturbative QCD, Foundations of Perturbative QCD, Cambridge University Press, Cambridge U.K. (2011).