
Physics 2011
Factorization Theorem For DrellYan At Low q_T And TransverseMomentum Distributions OnTheLightConeAbstract: We derive a factorization theorem for DrellYan process at low q_T using effective field theory methods. In this theorem all the obtained quantities are gauge invariant and the special role of the soft functionand its subtraction thereofis emphasized. We define transversemomentum dependent parton distribution functions (TMDPDFs) which are free from lightcone singularities while all the Wilson lines are defined onthelightcone. We show explicitly to first order in \alpha_s that the partonic Feynman PDF can be obtained from the newly defined partonic TMDPDF by integrating over the transverse momentum of the parton inside the hadron. We obtain a resummed expression for the TMDPDF, and hence for the cross section, in impact parameter space. The universality of the newly defined matrix elements is established perturbatively to first order in \alpha_s. The factorization theorem is validated to first order in \alpha_s and also the gauge invariance between Feynman and lightcone gauges.
