Methodology for measuring the transition electromagnetic form factor in the conversion decay ω → π0e+e– with the CMD-3 detector
https://doi.org/10.29235/1561-2430-2025-61-4-320-329
Abstract
This paper presents an improved methodology for measuring the transition electromagnetic form factor in the conversion decay ω → π0e+e– using data collected by the CMD-3 detector at the VEPP-2000 e+e– collider. The key improvement involves the application of a kinematic reconstruction technique under two distinct hypotheses: the signal hypothesis (ω → π0e+e–) and the dominant background hypothesis (ω → π+π–π0). This approach allows for a powerful suppression of 3π background, virtually eliminating it, and significantly narrows the invariant mass distribution of two photons from π0 decay in signal events. The refined π0 mass peak enhances the separation of the signal process from the remaining QED background (e+e– → e+e–γγ). To demonstrate the effectiveness of the method, it was applied to a subset of the data with an integrated luminosity of 13 pb⁻¹, accumulated near ω-meson mass. The analysis shows a significant improvement in the precision of the form factor F(q) measurement. The developed methodology paves the way for a more precise determination of the form factor slope parameter Λ ω−2 when applied to the full dataset, which has an integrated luminosity of approximately 50 pb⁻¹.
Keywords
conversion decay,
ω-meson,
transition electromagnetic form factor,
background subtraction,
CMD-3 detector
Supporting agencies: The authors express their sincere gratitude to the VEPP-2000 operation team for maintaining the superb performance of the collider throughout the data-taking period. We also extend our heartfelt thanks to all members of the CMD-3 collaboration for their essential contribution, unwavering support, and stimulating discussions, which made this study possible. The investigation was conducted with financial support of the grant of Russian Science Foundation no. 23-42-10025 (https://rscf.ru/project/23-42-10025/) and Belarusian Republican Foundation for Fundamental Research no. Ф23РНФ-118.
About the Authors
D. N. Grigoriev
Budker Institute of Nuclear Physics of the Siberian Branch of the Russian Academy of Sciences ; Novosibirsk State Technical University
Russian Federation
Russian Federation
Dmitry N. Grigoriev – Ph. D. (Physics and Mathematics), Leading Researcher; Associate Professor
11, Academician Lavrent’ev Ave., 630090, Novosibirsk
20, K. Marks Ave., 630073, Novosibirsk,
V. F. Kazanin
Budker Institute of Nuclear Physics of the Siberian Branch of the Russian Academy of Sciences ; Novosibirsk State University
Russian Federation
Russian Federation
Vasily F. Kazanin – Ph. D. (Physics and Mathematics), Leading Researcher; Senior Lecturer in the Department of Physics, Specialized Education-Scientific Center
11, Academician Lavrent’ev Ave., 630090, Novosibirsk
2, Pirogov Str., 630090, Novosibirsk
V. L. Ivanov
Budker Institute of Nuclear Physics of the Siberian Branch of the Russian Academy of Sciences
Russian Federation
Russian Federation
Vyacheslav L. Ivanov – Ph. D. (Physics and Mathematics), Researcher
11, Academician Lavrent’ev Ave., 630090, Novosibirsk
D. V. Shoukavy
B. I. Stepanov Institute of Physics of the National Academy of Sciences of Belarus
Belarus
Belarus
Dzmitry V. Shoukavy – Ph. D. (Physics and Mathematics), Head of the Center, B. I. Stepanov Institute of Physics
68-2, Nezavisimosti Ave., 220072, Minsk
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