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Polarizing fragmentation function and the $Λ$ polarization in $e^{+} e^{-}$ processes

M. Anselmino ^1,2,3,*, R. Kishore^3,†, and A. Mukherjee^3,‡

¹Dipartimento di Fisica, Università di Torino, Via P. Giuria 1, I-10125 Torino, Italy
²INFN, Sezione di Torino, Via P. Giuria 1, I-10125 Torino, Italy
³Department of Physics, Indian Institute of Technology Bombay, Mumbai-400076, India

^*mauro.anselmino@to.infn.it
^†raj.theps@gmail.com
^‡asmita@phy.iitb.ac.in

Phys. Rev. D 100, 014029 – Published 29 July, 2019

DOI: https://doi.org/10.1103/PhysRevD.100.014029

Abstract

The surprising polarization of $Λ$ ’s and other hyperons measured in many unpolarized hadronic processes, $p N \to Λ^{↑} X$ , has been a long-standing challenge for QCD phenomenology. One possible explanation was suggested, related to nonperturbative properties of the quark hadronization process, and encoded in the so-called polarizing fragmentation function (PFF). Recent Belle data have shown a nonzero $Λ$ polarization also in unpolarized $e^{+} e^{-}$ processes, $e^{+} e^{-} \to Λ X$ and $e^{+} e^{-} \to Λ h X$ . We consider the single inclusive case and the role of the PFFs. Adopting a simplified kinematics, we show how they can originate a polarization $P_{Λ} \neq 0$ and give explicit expressions for it in terms of the PFFs. Although the Belle data do not allow yet, in our approach, an extraction of the PFFs, some clear predictions are given, suggesting crucial measurements, and estimates of $P_{Λ}$ are computed, in qualitative agreement with the Belle data.

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Phys. Rev. D 100, 014029– Published 29 July, 2019

Vol. 100, Iss. 1 — 1 July 2019

Received 18 May 2019

DOI: https://doi.org/10.1103/PhysRevD.100.014029

Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP³.

Published by the American Physical Society

Physical Review D

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Polarizing fragmentation function and the $Λ$ polarization in $e^{+} e^{-}$ processes

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Polarizing fragmentation function and the $Λ$ polarization in $e^{+} e^{-}$ processes