Collins functions for pions from SIDIS and new e+e- data: a first glance at their transverse momentum dependence

TL;DR

This paper analyzes recent e+e- and SIDIS data to investigate the transverse momentum dependence of Collins functions for pions, comparing different evolution schemes and parameterizations to understand their impact on transversity distributions.

Contribution

It provides the first direct analysis of the transverse momentum dependence of Collins functions using new Belle, BaBar, and BESIII data, exploring different Q^2 evolution models.

Findings

Transversity distributions are extracted from combined SIDIS and e+e- data.

Different Q^2 evolution schemes yield consistent Collins function parameterizations.

Transverse momentum dependence significantly influences azimuthal asymmetries.

Abstract

New data from Belle and BaBar Collaborations on azimuthal asymmetries, measured in e+e- annihilations into pion pairs at Q^2=112 GeV^2, allow to take the first, direct glance at the transverse momentum dependence of the Collins functions, in addition to their z dependence. These data, together with available Semi-Inclusive Deep Inelastic Scattering (SIDIS) data on the Collins asymmetry, are simultaneously analysed in the framework of the generalised parton model assuming two alternative Q^2 evolution schemes and exploiting two different parameterisations for the Collins functions. The corresponding results for the transversity distributions are presented. Analogous data, newly released by the BESIII Collaboration, on e+e- annihilations into pion pairs at the lower Q^2 of 13 GeV^2, offer the possibility to explore the sensitivity of these azimuthal correlations on transverse momentum dependent evolution effects.