DOE OSTI · 2333063
Improved measurements of the Dalitz decays η / η ′ → γ e + e −
Abstract
Based on a data sample of 10 billion J / ψ events collected with the BESIII detector, improved measurements of the Dalitz decays η / η ′ → γ e + e − are performed, where the η and η ′ are produced through the radiative decays J / ψ → γ η / η ′ . The branching fractions of η → γ e + e − and η ′ → γ e + e − are measured to be ( 7.07 ± 0.05 ± 0.23 ) × 10 − 3 and ( 4.83 ± 0.07 ± 0.14 ) × 10 − 4 , respectively. Within the single-pole model, the parameter of electromagnetic transition form factor for η → γ e + e − is determined to be Λ η = ( 0.749 ± 0.027 ± 0.007 ) GeV / c 2 . Within the multipole model, we extract the electromagnetic transition form factors for η ′ → γ e + e − to be Λ η ′ = ( 0.802 ± 0.007 ± 0.008 ) GeV / c 2 and γ η ′ = ( 0.113 ± 0.010 ± 0.002 ) GeV / c 2 . The results are consistent with both theoretical predictions and previous measurements. The characteristic sizes of the interaction regions for the η and η ′ are calculated to be ( 0.645 ± 0.023 ± 0.007 ) fm and ( 0.596 ± 0.005 ± 0.006 ) fm , respectively. In addition, we search for the dark photon in η / η ′ → γ e + e − , and the upper limits of the branching fractions as a function of the dark photon are given at 90% confidence level. Published by the American Physical Society 2024
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Ablikim, M., Achasov, M. N., Adlarson, P., Afedulidis, O., Ai, X. C., Aliberti, R., Amoroso, A., An, Q., Bai, Y., Bakina, O., Balossino, I., Ban, Y., Bao, H. -R., Batozskaya, V., Begzsuren, K., Berger, N., Berlowski, M., Bertani, M., Bettoni, D., Bianchi, F., Bianco, E., Bortone, A., Boyko, I., Briere, R. A., Brueggemann, A., Cai, H., Cai, X., Calcaterra, A., Cao, G. F., Cao, N., Cetin, S. A., Chang, J. F., Chang, W. L., Che, G. R., Chelkov, G., Chen, C., Chen, C. H., Chen, Chao, Chen, G., Chen, H. S., Chen, M. L., Chen, S. J., Chen, S. L., Chen, S. M., Chen, T., Chen, X. R., Chen, X. T., Chen, Y. B., Chen, Y. Q., Chen, Z. J., Chen, Z. Y., Choi, S. K., Chu, X., Cibinetto, G., Cossio, F., Cui, J. J., Dai, H. L., Dai, J. P., Dbeyssi, A., de Boer, R. E., Dedovich, D., Deng, C. Q., Deng, Z. Y., Denig, A., Denysenko, I., Destefanis, M., De Mori, F., Ding, B., Ding, X. X., Ding, Y., Dong, J., Dong, L. Y., Dong, M. Y., Dong, X., Du, M. C., Du, S. X., Duan, Z. H., Egorov, P., Fan, Y. H., Fang, J., Fang, S. S., Fang, W. X., Fang, Y., Fang, Y. Q., Farinelli, R., Fava, L., Feldbauer, F., Felici, G., Feng, C. Q., Feng, J. H., Feng, Y. T., Fischer, K., Fritsch, M., Fu, C. D., Fu, J. L., Fu, Y. W., Gao, H., Gao, Y. N., Gao, Yang, Garbolino, S.. 2024-04-03. Improved measurements of the Dalitz decays η / η ′ → γ e + e −. https://doi.org/10.1103/physrevd.109.072001
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