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Measurement of transverse polarization of Λ and hyperons inside jets in unpolarized proton-proton collisions at GeV

  • STAR Collaboration
  • Texas A&M University
  • Czech Technical University in Prague
  • Joint Institute for Nuclear Research
  • Panjab University

Research output: Contribution to journal › Article › peer-review

Abstract

A surprisingly large transverse polarization of Λ hyperons in unpolarized hadron-nucleon/nucleus collisions has been observed for 50 years, and the origin of this polarization remains an important open question. Recently, theoretical frameworks have advanced in describing this puzzle with the polarizing fragmentation function (PFF). We report the first measurement of Λ and transverse polarization inside jets in unpolarized proton-proton collisions, which is directly attributed to the PFF. The polarization is measured as a function of the jet transverse momentum, the fraction of the jet momentum carried by hyperons, and the transverse momentum of hyperons relative to the jet axis. Covering a wide jet-energy range, these data provide the first constraints on the gluon PFF and allow tests of TMD evolution and its universality.

Original languageEnglish
Article number50
JournalJournal of High Energy Physics
Volume2026
Issue number6
DOIs
StatePublished - Jun 2026

Keywords

  • Hadron-Hadron Scattering
  • Jets
  • Polarization
  • Proton-Proton Scattering

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