Observation of Transverse Λ/¯Λ Hyperon Polarization in e+e− Annihilation at Belle

Abstract

We report the first observation of the spontaneous polarization of Λ and ¯Λ hyperons transverse to the production plane in e+e− annihilation, which is attributed to the effect arising from a polarizing fragmentation function. For inclusive Λ/¯Λ production, we also report results with subtracted feed-down contributions from Σ0 and charm. This measurement uses a dataset of 800.4 fb−1 collected by the Belle experiment at or near a center-of-mass energy of 10.58 GeV. We observe a significant polarization that rises with the fractional energy carried by the Λ/¯Λ hyperon.