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

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.

Automated summary

Recent experimental measurements have explored the relationship between cross sections for single hadron production and hadron-pair production in e+e- annihilations within the framework of TMD factorization. A scheme has been proposed to relate TMD parton densities in 1-hadron and 2-hadron processes, addressing the regularization of rapidity divergences and the arbitrariness of cut-offs. This allows for global phenomenological studies of TMD physics and the analysis of data from different hadron classes.