Semi-inclusive production of two back-to-back hadron pairs in $e^+e^-$ annihilation revisited

TL;DR

This paper revisits the cross section for back-to-back hadron pair production in $e^+e^-$ annihilation, resolving discrepancies in dihadron fragmentation functions and explaining the nonobservation of certain asymmetries in experiments.

Contribution

The authors rederive the fully differential cross section at leading twist, correcting a kinematic mistake and clarifying the relation between IFF definitions in SIDIS and $e^+e^-$ processes.

Findings

Discrepancy between IFF definitions in SIDIS and $e^+e^-$ annihilation is resolved.

The azimuthal asymmetry for $G_1^ot$ in $e^+e^-$ vanishes, explaining experimental nonobservation.

Alternative methods to extract $G_1^ot$ are discussed.

Abstract

The cross section for back-to-back hadron pair production in $e^+e^-$ annihilation provides access to the dihadron fragmentation functions (DiFF) needed to extract nucleon parton distribution functions from the semi-inclusive deep inelastic scattering (SIDIS) experiments with two detected final state hadrons. Particular attention is given to the so-called interference DiFF (IFF), which makes it possible to extract the transversity parton distribution of the nucleon in the collinear framework. However, previously unnoticed discrepancies were recently highlighted between the definitions of the IFFs appearing in the collinear kinematics when reconstructed from DiFFs entering the unintegrated fully differential cross sections of SIDIS and $e^+e^-$ annihilation processes. In this work, to clarify this problem we rederive the fully differential cross section for $e^+e^-$ annihilation at the leading-twist approximation. We find a mistake in the definition of the kinematics in the original expression that systematically affects a subset of terms and that leads to two significant consequences. First, the discrepancy between the IFF definitions in the cross sections for SIDIS and $e^+e^-$ annihilation is resolved. Second, the previously derived azimuthal asymmetry for accessing the helicity dependent DiFF $G_1^\perp$ in $e^+e^-$ annihilation vanishes, which explains the nonobservation of this asymmetry in the recent experimental searches by the ${\tt BELLE}$ Collaboration. We discuss the recently proposed alternative option to extract $G_1^\perp$.