Transversity and Collins Functions: from e+e-→ h1h2X to SIDIS Processes
U. D’Alesio, Mauro Anselmino, M. Boglione, A.M. Kotzinian, F. Murgia, Alexei Prokudin · 2007
We present [1] the first simultaneous extraction of the transversity distribution and the Collins fragmentation function, obtained through a combined analysis of experimental data on azimuthal asymmetries in semi-inclusive deep inelastic scattering (SIDIS), from the HERMES and COMPASS Collaborations, and in e + e -→ h1h2X processes, from the Belle Collaboration.Among the three leading twist parton distributions, that contain basic information on the internal structure of nucleons, the transversity distribution is the most difficult to access.Due to its chiral-odd nature it can only appear in physical processes which require a quark helicity flip.At present the most accessible channel is the SIDIS process with a polarized target, where the corresponding azimuthal asymmetry, A sin(φS +φ h ) U T , involves the transversity distribution coupled to the Collins fragmentation function [2], also unknown.Indeed it has received a lot of attention in the ongoing experimental programs of HERMES [3], COMPASS [4], and JLab Collaborations.A crucial breakthrough in this strategy has recently been achieved with the independent measurement of the Collins function via the azimuthal correlation observed in the two-pion production in e + e -annihilation by the Belle Collaboration at KEK [5].Let us start with the e + e -→ h 1 h 2 X process.We choose the reference frame so that the elementary e + e -→ q q scattering occurs in the xz plane, with the back-to-back quark and antiquark moving along the ẑ-axis identified as the jet thrust axis.The cross section corresponding to this process can be expressed as (see Ref. [6]):