Probing transversity by measuring $\Lambda$ polarisation in SIDIS

TL;DR

This paper reports on measurements of $ ext{Lambda}$ hyperon polarization in SIDIS to probe transversity quark distributions, finding no significant polarization signal within experimental uncertainties, thus providing constraints on theoretical models.

Contribution

First measurement of $ ext{Lambda}$ hyperon polarization in SIDIS off transversely polarized protons to access transversity distributions.

Findings

No significant $ ext{Lambda}$ polarization observed.

Results constrain transversity models.

Data consistent with zero polarization within uncertainties.

Abstract

Based on the observation of sizeable target-transverse-spin asymmetries in single-hadron and hadron-pair production in Semi-Inclusive measurements of Deep Inelastic Scattering (SIDIS), the chiral-odd transversity quark distribution functions $h_1^q$ are nowadays well established. Several possible channels to access these functions were originally proposed. One candidate is the measurement of the polarisation of $\Lambda$ hyperons produced in SIDIS off transversely polarised nucleons, where the transverse polarisation of the struck quark might be transferred to the final-state hyperon. In this article, we present the COMPASS results on the transversity-induced polarisation of $\Lambda$ and $\bar{\Lambda}$ hyperons produced in SIDIS off transversely polarised protons. Within the experimental uncertainties, no significant deviation from zero was observed. The results are discussed in the context of different models taking into account previous experimental results on $h_1^u$ and $h_1^d$.