Collins-Soper Equation for the Energy Evolution of Transverse-Momentum   and Spin Dependent Parton Distributions
  The hadron-energy evolution (Collins and Soper) equation for all the leading-twist transverse-momentum and spin dependent parton distributions is derived in the impact parameter space. Based on the result, we present resummation formulas for the spin structure functions in the semi-inclusive deep inelastic scattering. 
Ahmad Idilbi, Xiangdong Ji, Jian-Ping Ma, Feng Yuan