1. For a recent review of experiments, see e.g., A. D. Krisch, Hard collisions of spinning protons: Past, present and future, Eur. Phys. J. A 31(4), 417 (2007), there are also a number of reviews on this topic, see e.g., Z. T. Liang and C. Boros, Int. J. Mod. Phys. A 15, 927 (2000), V. Barone, F. Bradamante, and A. Martin, Transverse-spin and transverse-momentum effects in high-energy processes, Prog. Part. Nucl. Phys. 65(2), 267 (2010)
2. Z. T. Liang, Three dimensional imaging of the nucleon–TMD (theory and phenomenology), arXiv: 1502.03896 [hep-ph], Plenary talk at the 21st International Symposium on Spin Physics, October 20–24, 2014
3. D. Boer, Overview of TMD evolution, arXiv: 1502.00899 [hep-ph], Invited talk at the 21st International Symposium on Spin Physics, October 20–24, 2014
4. J. Collins, TMD theory, factorization and evolution, Int. J. Mod. Phys. Conf. Ser. 25, 1460001 (2014), arXiv: 1307.2920
5. There are definitely cases where factorization might break down, see e.g., J. P. Ma, J. X. Wang, and S. Zhao, Breakdown of QCD factorization for P-wave quarkonium production at low transverse momentum, Phys. Lett. B 737, 103 (2014), arXiv: 1405.3373 [hep-ph], and the references given there