Cover Story (Issue 5, 2026): Determinationof Fragmentation Functions from Charge Asymmetries in Hadron Production
Author: Hongxi Xing (South China NormalUniversity, Guangzhou, China)
Fragmentation Functions (FFs) arefundamental non-perturbative quantities in Quantum Chromodynamics that encodethe probability density of a parton transitioning into a specific hadron. Theprecise determination of these functions from global analysis of experimentaldata has been a long-standing pursuit in high-energy physics, playing anindispensable role in understanding nucleon structure, nuclear effects, and thehadronization mechanism. With the upcoming era of electron-ion collidersdemanding unprecedented precision, the accurate extraction of FFs has becomeincreasingly critical, driving the search for clean probes to directlyconstrain these functions and thereby reveal the fundamental nature of colorconfinement.
A recent study [1] proposes a novel methodfor extracting the non-singlet (NS) component of FFs for light chargedhadrons—pions and kaons—from charge asymmetries measured in bothsingle-inclusive electron-positron annihilation (SIA) and semi-inclusivedeep-inelastic scattering (SIDIS). Working within the framework of QCDcollinear factorization at the state-of-the art accuracy ofnext-to-next-to-leading order (NNLO), the authors demonstrate that a remarkablysimple three-parameter functional form can describe the full world data on pioncharge asymmetry with excellent fit quality. Through a comprehensive analysisincorporating world data from the HERMES, COMPASS, ABCMO, and SLDexperiments—several of which are included in a global analysis at NNLO for thefirst time—the study achieves a precise determination of the large-momentum-fractionscaling index β ≈ 0.7, favoring predictions from the Nambu–Jona-Lasinio modeland disfavoring the β ∼ 2 expectationsfrom perturbative QCD counting rules and Dyson-Schwinger equation approaches.In a joint fit of pion and kaon data, the analysis further determines astrangeness suppression factor of approximately 0.5 and uncovers a strikinguniversality in the non-singlet fragmentation of light mesons. Moreover, theextracted FFs are systematically compared against predictions from variousglobal analyses, the Field-Feynman model, continuum Schwinger methods, andMonte Carlo event generators such as PYTHIA8 and JETSET, revealing notabledifferences across these approaches.
In conclusion, this work establishes apowerful and theoretically clean methodology for probing the non-singlet sectorof FFs through charge asymmetry observables, and provides a valuable benchmarkfor testing non-perturbative QCD models and Monte Carlo event generators. Theseresults significantly advance our quantitative understanding of hadronizationand serve as crucial input for the physics programs of future electron-ioncolliders.
[1] J. Gao, C. Y. Liu, and B. Zhou, Chin.Phys. C 50, 053101 (2026), arXiv:2507.14637 [hep-ph]
