Angular ordering effects in TMD parton distribution functions and Drell-Yan $q_{\bot}$ spectra

Abstract

We present new results of our studies of soft-gluon angular ordering effects on the evolution of both collinear and transverse momentum dependent (TMD) parton distribution functions, and discuss their implications for precision predictions of Drell-Yan transverse momentum spectra at the LHC. Our method is based on the parton branching (PB) approach. We compare this with the implementation of angular ordering in the Kimber-Martin-Ryskin-Watt (KMRW) approach and with the Collins-Soper-Sterman (CSS) approach. We illustrate numerically the effects of different ordering scenarios ($p_{\bot}$, angular ordering), including definitions of the soft-gluon resolution scale and scale in the running coupling, on the theoretical accuracy of predictions in the low transverse momentum region of Drell-Yan spectra measured at the LHC.