Observation of Transverse $\Lambda /\bar{\Lambda }$ Hyperon Polarization in $e^{+}{e}^{-}$ Annihilation at Belle

Abstract

We report the first observation of the spontaneous polarization of $\Lambda$ and $\bar{\Lambda }$ hyperons transverse to the production plane in $e^{+}{e}^{-}$ annihilation, which is attributed to the effect arising from a polarizing fragmentation function. For inclusive $\Lambda /\bar{\Lambda }$ production, we also report results with subtracted feed-down contributions from ${\Sigma }^0$ 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 $\Lambda /\bar{\Lambda }$ hyperon.

arXiv comment7 pages, 3 figures, plus supplemental material. Submitted to Phys. Rev. Lett

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