Speaker
Description
We present the Parton Branching (PB) method for the evolution of both collinear and transverse momentum dependent (TMD) parton distribution functions (PDFs). This method enables one to take into account explicitly the kinematics at each branching in the parton cascade and to study in detail the dynamics of QCD evolution, including different ordering scenarios (pt, virtuality, angular ordering), especially different definitions of the soft gluon resolution scale parameter and renormalization scale in the strong coupling alpha_s. The method was implemented in xFitter package and two TMD PDF sets, both with angular ordering definition to calculate kt and differing in renormalization scale choice, were obtained from a fit to precision HERA DIS data. Obtained TMDs were applied to LHC measurements. The PB method can be also used to construct parton shower (PS) algorithm which follows obtained TMDs. This is an important step towards precise predictions for high energy observables where ME and PS follows the same TMD and no adjustment of the kinematics after showering is needed. The PB method can be also compared with other methods to obtain TMDs as Collins-Soper-Sterman (CSS) approach.
