Probing the Color-Octet Mechanism via Dihadron Fragmentation in χ b Decays

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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 χ b 2 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 ρ 8 between CO and CS matrix elements. Focusing on e + e − → ϒ ( 2 S ) → γ χ b 2 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, ρ 8 could be determined with sufficient precision to address the long-standing discrepancy between the lattice calculations and phenomenological determinations.
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Funding Information
  • National Natural Science Foundation of China (12547174)
  • National Natural Science Foundation of China (12422506)
  • National Natural Science Foundation of China (12342502)
  • Chinese Academy of Sciences (E429A6M1)
  • China Postdoctoral Science Foundation (2026M793746)
  • Fundamental Research Funds for the Central Universities (buctrc202432)

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