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 h1q are nowadays well established. Several possible channels to access these functions were originally proposed. One candidate is the measurement of the polarisation of Λ 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 Λ and Λ¯ 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 h1u and h1d.

Highlights

  • The chiral-odd transversity quark distribution functions hq1(x), hereafter referred to as transversity, were introduced as independent Parton Distribution Functions (PDFs) of the nucleon several decades ago [1,2,3,4]

  • The analysis presented here was performed using the data collected by COMPASS in 2007 and 2010 with a 160 GeV/c longitudinally polarised muon beam from the CERN SPS and a transversely polarised NH3 target with proton polarisation PT = 0.80 and dilution factor f = 0.15

  • 2010 201 421 ± 466 99 552 ± 336 total 296 546 ± 562 144 463 ± 405 event generator LEPTO based on the Lund string model [31], 63% of the Λ and 68% of the Λhyperons produced in the COMPASS kinematic regime are estimated to originate from direct string fragmentation [32]

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Summary

Introduction

The chiral-odd transversity quark distribution functions hq1(x), hereafter referred to as transversity, were introduced as independent Parton Distribution Functions (PDFs) of the nucleon several decades ago [1,2,3,4]. The Λ(Λ) polarisation from the 2002-2004 data with a transversely polarised deuteron target [25] was found to be compatible with zero, as expected from the cancellation of u and d quark transversity (see Sec. 4.3). This measurement, suffered from limitations in statistical power and in spectrometer acceptance and from the lack of particle identification for a part of the data set. The upcoming 2021/2022 run using a transversely polarised deuteron target [26] will be of great importance in drawing more definite conclusions

Data selection and available statistics
Interpretation of the results and predictions for future measurements
Interpretation of the measured Λpolarisation
Interpretation of the measured Λ polarisation
Projections for future data taking with transversely polarised deuterons
Findings
Summary and outlook
Full Text
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