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

The STAR collaboration

doi:10.1007/JHEP06(2026)050

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

The STAR collaboration

Texas A&M University
Czech Technical University in Prague
Joint Institute for Nuclear Research
Panjab University
Variable Energy Cyclotron Centre India
Russian Research Centre Kurchatov Institute
Moscow Engineering Physics Institute
Kent State University
Fudan University
Abilene Christian University
Universidad de Tarapacá
Shandong University
Indian Institute of Science Education and Research, Berhampur
University of California at Riverside
Indian Institute of Science Education and Research, Tirupati
University of Jammu
Stony Brook University
Ohio State University
University of Houston
Chinese Academy of Sciences
Yale University
University of California at Davis
Lawrence Berkeley National Laboratory
Purdue University
Indiana University Bloomington
National Institute of Technology, Durgapur
Central China Normal University
Guangxi Normal University
Tsinghua University
University of California at Los Angeles
Brookhaven National Laboratory
University of California at Berkeley

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 language	English
Article number	50
Journal	Journal of High Energy Physics
Volume	2026
Issue number	6
DOIs	https://doi.org/10.1007/JHEP06(2026)050
State	Published - Jun 2026

Keywords

Hadron-Hadron Scattering
Jets
Polarization
Proton-Proton Scattering

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10.1007/JHEP06(2026)050

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@article{b4fe433d230b4cee8f8f5687f78cb15e,

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

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.",

keywords = "Hadron-Hadron Scattering, Jets, Polarization, Proton-Proton Scattering",

author = "\{The STAR collaboration\} and Aboona, \{B. E.\} and J. Adam and G. Agakishiev and I. Aggarwal and Aggarwal, \{M. M.\} and Z. Ahammed and A. Aitbayev and I. Alekseev and E. Alpatov and Alshammri, \{A. K.\} and A. Aparin and S. Aslam and J. Atchison and Averichev, \{G. S.\} and V. Bairathi and X. Bao and P. Barik and K. Barish and S. Behera and P. Bhagat and A. Bhasin and S. Bhatta and Bordyuzhin, \{I. G.\} and Brandenburg, \{J. D.\} and Brandin, \{A. V.\} and C. Broodo and Cai, \{X. Z.\} and H. Caines and \{Calderon de la Barca Sanchez\}, M. and D. Cebra and J. Ceska and I. Chakaberia and Chang, \{Y. S.\} and Z. Chang and A. Chatterjee and D. Chen and Chen, \{J. H.\} and L. Chen and Q. Chen and W. Chen and Z. Chen and J. Cheng and Y. Cheng and W. Christie and X. Chu and S. Corey and Crawford, \{H. J.\} and A. Deshpande and J. Jia and R. Lacey",

note = "Publisher Copyright: {\textcopyright} The Author(s) 2026.",

year = "2026",

month = jun,

doi = "10.1007/JHEP06(2026)050",

language = "English",

volume = "2026",

journal = "Journal of High Energy Physics",

issn = "1126-6708",

number = "6",

}

TY - JOUR

T1 - Measurement of transverse polarization of Λ and hyperons inside jets in unpolarized proton-proton collisions at GeV

AU - The STAR collaboration

AU - Aboona, B. E.

AU - Adam, J.

AU - Agakishiev, G.

AU - Aggarwal, I.

AU - Aggarwal, M. M.

AU - Ahammed, Z.

AU - Aitbayev, A.

AU - Alekseev, I.

AU - Alpatov, E.

AU - Alshammri, A. K.

AU - Aparin, A.

AU - Aslam, S.

AU - Atchison, J.

AU - Averichev, G. S.

AU - Bairathi, V.

AU - Bao, X.

AU - Barik, P.

AU - Barish, K.

AU - Behera, S.

AU - Bhagat, P.

AU - Bhasin, A.

AU - Bhatta, S.

AU - Bordyuzhin, I. G.

AU - Brandenburg, J. D.

AU - Brandin, A. V.

AU - Broodo, C.

AU - Cai, X. Z.

AU - Caines, H.

AU - Calderon de la Barca Sanchez, M.

AU - Cebra, D.

AU - Ceska, J.

AU - Chakaberia, I.

AU - Chang, Y. S.

AU - Chang, Z.

AU - Chatterjee, A.

AU - Chen, D.

AU - Chen, J. H.

AU - Chen, L.

AU - Chen, Q.

AU - Chen, W.

AU - Chen, Z.

AU - Cheng, J.

AU - Cheng, Y.

AU - Christie, W.

AU - Chu, X.

AU - Corey, S.

AU - Crawford, H. J.

AU - Deshpande, A.

AU - Jia, J.

AU - Lacey, R.

PY - 2026/6

Y1 - 2026/6

N2 - 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.

AB - 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.

KW - Hadron-Hadron Scattering

KW - Jets

KW - Polarization

KW - Proton-Proton Scattering

UR - https://www.scopus.com/pages/publications/105041637113

U2 - 10.1007/JHEP06(2026)050

DO - 10.1007/JHEP06(2026)050

M3 - Article

AN - SCOPUS:105041637113

SN - 1126-6708

VL - 2026

JO - Journal of High Energy Physics

JF - Journal of High Energy Physics

IS - 6

M1 - 50

ER -

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

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Keywords

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