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ISSN - 03702693, Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics, 1999, vol. 462, p. 371-379

First observation of the φ → π+ π- γ decay

Akhmetshin R. R., Anashkin E. V., Anagaus M., Aulchenko V. M., Banzarov V. S., Barkov L. M., Bashtovoy N. S., Bondar A. E., Bondarev D. V., Bragin A. V., Chernyak D. V., Dvoretsky A. S., Eidelman S. I., Fedotovich G. V., Gabyshev N. I., Grebeniuk A. A., Grigoriev D. N., Ivanov P. M., Karpov S. V., Kazanin V. F., Khazin B. I., Koop I. A., Krokovny P. P., Kurdadze L. M., Kuzmin A. S., Logashenko I. B., Lukin P. A., Lysenko A. P., Mikhailov K. Yu, Nesterenko I. N., Okhapkin V. S., Perevedentsev E. A., Panich E. A., Popov A. S., Purlatz T. A., Root N. I., Ruban A. A., Ryskulov N. M., Shamov A. G., Shatunov Yu M., Shwartz B. A., Sibidanov A. L., Sidorov V. A., Skrinsky A. N., Smakhtin V. P., Snopkov I. G., Solodov E. P., Stepanov P. Yu, Sukhanov A. I., Titov V. M., Yudin Yu V., Zverev S. G., Thompson L. A.

Radiative decays of the φ meson have been studied using a data sample of about 20 million φ decays collected by the CMD-2 detector at VEPP-2M collider in Novosibirsk. From selected e+e-→ π+π-γ events the φ → π+π-γ decay has been observed for the first time. Under the assumption that the intermediate f0(980)γ state dominates in the φ → π+π-γ decay, the corresponding branching ratio is Br(φ→f0(980)γ) = (1.93 ± 0.46 ± 0.50) × 10-4. Selected e+e-→ μ+μ-γ events were used to obtain Br(φ→ μ+μ-γ) = (1.43 ± 0.45 ± 0.14) × 10-5 for Eγ > 20 MeV. Using the same data sample, upper limits at 90% CL have been obtained for the C-violating decay of the φ: Br(φ→ ργ) < 1.2 × 10-5; and for the P- and CP-violating decay of the η: Br(η→π+π-) <3.3 × 10-4. © 1999 Published by Elsevier Science B.V. All rights reserved.