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High Energy Physics - Experiment

arXiv:2509.17487 (hep-ex)
[Submitted on 22 Sep 2025 (v1), last revised 13 May 2026 (this version, v3)]

Title:Measurement of transverse polarization of $Λ$ and $\barΛ$ hyperons inside jets in $pp$ collisions at $\sqrt{s}=200$ GeV

Authors:STAR Collaboration: B. E. Aboona, J. Adam, G. Agakishiev, I. Aggarwal, M. M. Aggarwal, Z. Ahammed, A. Aitbayev, I. Alekseev, E. Alpatov, A. K. Alshammri, A. Aparin, S. Aslam, J. Atchison, G. S. Averichev, V. Bairathi, X. Bao, P. Barik, K. Barish, S. Behera, P. Bhaga t, A. Bhasin, S. Bhatta, I. G. Bordyuzhin, J. D. Brandenburg, A. V. Brandin, C. Broodo, X. Z. Cai, H. Caines, M. Calderón de la Barca Sánchez, D. Cebra, J. Ceska, I. Chakaberia, Y. S. Chang, Z. Chang, A. Chatterjee, D. Chen, J. H. Chen, L. Chen, Q. Chen, W. Chen, Z. Chen, J. Cheng, Y. Cheng, W. Christie, X. Chu, S. Corey, H. J. Crawford, G. Dale-Gau, A. Das, D. De Souza Lemos, T. G. Dedovich, I. M. Deppner, A. A. Derevschikov, A. Deshpande, A. Dhamija, A. Dimri, P. Dixit, X. Dong, J. L. Drachenberg, E. Duckworth, J. C. Dunlop, Y. S. El-Feky, J. Engelage, G. Eppley, S. Esumi, O. Evdokimov, O. Eyser, B. Fan, Y. Fang, R. Fatemi, S. Fazio, H. Feng, Y. Feng, E. Finch, Y. Fisyak, F. A. Flor, B. Fu, C. Fu, T. Fu, T. Gao, Y. Gao, G. Garcia, F. Geurts, A. Gibson, A. Giri, K. Gopal, M. Gor don, X. Gou, D. Grosnick, A. Gu, J. Gu, A. Gupta, A. Hamed, R. J. Hamilton, J. Han, X. Han, M. D. Harasty, J. W. Harris, H. Harrison-Smith et al. (290 additional authors not shown)  You must enable JavaScript to view entire author list.
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Abstract:A surprisingly large transverse polarization of $\Lambda$ 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 $\Lambda$ and $\overline{\Lambda}$ 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 $\Lambda$($\overline{\Lambda}$) hyperons, and the transverse momentum of $\Lambda(\overline{\Lambda})$ 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.
Subjects: High Energy Physics - Experiment (hep-ex)
Cite as: arXiv:2509.17487 [hep-ex]
  (or arXiv:2509.17487v3 [hep-ex] for this version)
  https://doi.org/10.48550/arXiv.2509.17487
Journal reference: J. High Energ. Phys. 2026, 50 (2026)
Related DOI: https://doi.org/10.1007/JHEP06%282026%29050

Submission history

From: Taoya Gao [view email]
[v1] Mon, 22 Sep 2025 08:18:57 UTC (329 KB)
[v2] Sat, 21 Feb 2026 01:00:04 UTC (344 KB)
[v3] Wed, 13 May 2026 13:07:13 UTC (346 KB)
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