DOE OSTI · 2555922
Study of η → π + π − l + l −
Abstract
Using a sample of ( 10087 ± 44 ) × 10 6 J / ψ events accumulated with the BESIII detector, we analyze the decays η → π + π − l + l − ( l = e or μ ) via the process J / ψ → γ η . The branching fraction of η → π + π − e + e − is measured to be B ( η → π + π − e + e − ) = ( 3.07 ± 0.1 2 stat ± 0.1 9 syst ) × 10 − 4 . No signal events are observed for the η → π + π − μ + μ − decay, leading to an upper limit on the branching fraction of B ( η → π + π − μ + μ − ) < 4.0 × 10 − 7 at the 90% confidence level. Furthermore, the C P -violation asymmetry parameter is found to be A C P ( η → π + π − e + e − ) = ( − 4.04 ± 4.6 9 stat ± 0.1 4 syst ) % , showing no evidence of C P -violation with current statistics. Additionally, we extract the transition form factor from the decay amplitude of η → π + π − e + e − . Finally, axionlike particles are searched for via the decay η → π + π − a , a → e + e − , and upper limits on this branching fraction relative to that of η → π + π − e + e − are presented as a function of the axionlike particle mass in the range 5 – 200 MeV / c 2 . Published by the American Physical Society 2025
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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., Che, G. R., Chelkov, G., Chen, C., Chen, C. H., Chen, Chao, Chen, G., Chen, H. S., Chen, H. Y., 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., 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, Y. Y., 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., Fritsch, M., Fu, C. D., Fu, J. L., Fu, Y. W., Gao, H., Gao, X. B., Gao, Y. N., Gao, Yang, Garbolino, S.. 2025-04-11. Study of η → π + π − l + l −. https://doi.org/10.1103/physrevd.111.072008
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