TMDs from Monte Carlo event generators

TL;DR

This paper introduces PS2TMD, a method to extract effective TMD parton distributions from Monte Carlo parton showers, validated through reconstruction of PB-TMDs and analysis of kinematic effects.

Contribution

Development and validation of PS2TMD, a novel method to determine effective TMDs from standard Monte Carlo parton showers.

Findings

Successful reconstruction of PB-TMDs with different settings

Identification of kinematic shifts affecting momentum distributions

Influence of reconstruction definitions on PDFs

Abstract

Transverse Momentum Dependent (TMD) parton distributions are a very powerful concept for the description of low and high transverse momentum effects in high energy collisions. The Parton Branching (PB) method provides TMD distributions which can be used in parton shower simulations, as already implemented in \cascade\ Monte Carlo event generator. This report gives a description of the work done during the DESY summer student program 2021, young scientists from very different time zones connecting from remote twice a day for 8 weeks, to develop a method, PS2TMD, that allows to determine effective TMDs from the standard Monte Carlo parton showers. This method is validated and implemented to successfully reconstruct the PB-TMDs with different configuration settings. We also discuss kinematic shifts in longitudinal momentum distributions from initial state showering and point out the sizable influence of different reconstruction definitions on both collinear and transverse momentum PDFs. %the nonperturbative dependence on longitudinal and transverse degrees of freedom is fully coupled.