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Probing the Color-Octet Mechanism via Dihadron Fragmentation in χb Decays

Zhi-Guo He1, Guanghui Li2,3, Yu-Jie Tian2,3, Xin-Kai Wen2,4,*, and Bin Yan2,5,†

  • *Contact author: xinkaiwen@ihep.ac.cn
  • †Contact author: yanbin@ihep.ac.cn
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Phys. Rev. Lett. 137, 131903 – Published 25 September, 2026

DOI: https://doi.org/10.1103/ntf8-k9rh

Abstract

The color-octet (CO) mechanism is a cornerstone of nonrelativistic QCD, yet knowledge of its long-distance matrix elements remains limited, preventing stringent tests of the theory. We demonstrate that the Artru-Collins asymmetry in hadronic decays of the P-wave bottomonium state χb2 provides a direct probe of CO dynamics. At leading order, the asymmetry arises exclusively from the CO decay channel, whereas the color-singlet (CS) contribution affects only the unpolarized rate, so that a nonzero signal constitutes unambiguous evidence of the CO mechanism. This observable provides a novel way to extract the ratio ρ8 between CO and CS matrix elements. Focusing on e+e−→ϒ(2S)→γχb2 at Belle, we show that the asymmetric beam configuration preserves the asymmetry in the laboratory frame and avoids the strong suppression present in the center-of-mass frame. With the Belle II dataset, ρ8 could be determined with sufficient precision to address the long-standing discrepancy between the lattice calculations and phenomenological determinations.

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Outline

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Phys. Rev. Lett. 137, 131903– Published 25 September, 2026
  • Received 27 March 2026
  • Revised 17 August 2026
  • Accepted 9 September 2026
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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.

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