Universality-breaking effects in $e^+e^-$ hadronic production processes

TL;DR

This paper investigates the effects of process-dependent soft factors on the universality of transverse momentum dependent (TMD) distributions in $e^+e^-$ hadronic production, proposing a scheme to relate different processes within the Collins-Soper-Sterman framework.

Contribution

It introduces a scheme to connect TMD parton densities in 1-hadron and 2-hadron processes, separating non-perturbative and perturbative contributions to facilitate global TMD phenomenology.

Findings

Proposes a method to relate TMD densities across different processes.

Addresses regularization of rapidity divergences with a gauge transformation-like mechanism.

Enables combined analysis of diverse hadron production data.

Abstract

Recent BELLE measurements provide the cross section for single hadron production in $e^+e^-$ annihilations, differential in thrust and in the hadron transverse momentum with respect to the thrust axis. Universality breaking effects due to process-dependent soft factors make it very difficult to relate this cross sections to those corresponding to hadron-pair production in $e^+e^-$ annihilations, where transverse momentum dependent (TMD) factorization can be applied. The correspondence between these two cross sections is examined in the framework of the Collins-Soper-Sterman factorization, in the collinear as well as in the TMD approach. We propose a scheme that allows to relate the TMD parton densities defined in 1-hadron and in 2-hadron processes, neatly separating, within the soft and collinear parts, the non-perturbative terms from the contributions that can be calculated perturbatively. The regularization of rapidity divergences introduces cut-offs, the arbitrariness of which will be properly reabsorbed by means of a mechanism closely reminiscent of a gauge transformation. In this way, we restore the possibility to perform global phenomenological studies of TMD physics, simultaneously analyzing data belonging to different hadron classes.