Spin dependent fragmentation function at Belle

TL;DR

This paper reports the measurement of the Collins fragmentation function using azimuthal asymmetries in pion pairs from Belle data, aiding the understanding of quark transverse spin distributions.

Contribution

First measurement of the Collins fragmentation function at Belle using azimuthal asymmetries in pion pairs, providing essential data for transversity studies.

Findings

Measured azimuthal asymmetries for pion pairs

Provided data on the Collins fragmentation function

Supported the nonzero nature of chiral-odd FFs

Abstract

The measurement of the so far unknown chiral-odd quark transverse spin distribution in either semi-inclusive DIS (SIDIS) or inclusive measurements in pp collisions at RHIC has an additional chiral-odd fragmentation function appearing in the cross section. These chiral-odd fragmentation functions (FF) can for example be the so-called Collins FF or the Interference FF. HERMES has given a first hint that these FFs are nonzero, however in order to measure the transversity one needs these FFs to be precisely known. We have used 29.0 fb$^{-1}$ of data collected by the Belle experiment at the KEKB $e^+e^-$ collider to measure azimuthal asymmetries for different charge combinations of pion pairs and thus access the Collins FF.