Breakdown of QCD Factorization for P-Wave Quarkonium Production at Low   Transverse Momentum
  Quarkonium production at low transverse momentum in hadron collisions can be used to extract Transverse-Momentum-Dependent(TMD) gluon distribution functions, if TMD factorization holds there. We show that TMD factorization for the case of P-wave quarkonium with $J^{PC}=0^{++}, 2^{++}$ holds at one-loop level, but is violated beyond one-loop level. TMD factorization for other P-wave quarkonium is also violated already at one-loop. 
J.P. Ma, J.X. Wang and S. Zhao
hep-ph