Triangle Singularity as the Origin of the a 1 ( 1420 )

• Published in: Physical review letters 2021-08, Vol.127 (8), Article 082501
• Main Authors: Alexeev, G. D., Alexeev, M. G., Amoroso, A., Andrieux, V., Anosov, V., Antoshkin, A., Augsten, K., Augustyniak, W., Azevedo, C. D. R., Badełek, B., Balestra, F., Ball, M., Barth, J., Beck, R., Bedfer, Y., Berenguer Antequera, J., Bernhard, J., Bodlak, M., Bradamante, F., Bressan, A., Burtsev, V. E., Chang, W.-C., Chatterjee, C., Chiosso, M., Chumakov, A. G., Chung, S.-U., Cicuttin, A., Correia, P. M. M., Crespo, M. L., D’Ago, D., Dalla Torre, S., Dasgupta, S. S., Dasgupta, S., Denisenko, I., Denisov, O. Yu, Donskov, S. V., Doshita, N., Dreisbach, Ch, Dünnweber, W., Dusaev, R. R., Efremov, A., Eversheim, P. D., Faccioli, P., Faessler, M., Finger, M., Fischer, H., Franco, C., Friedrich, J. M., Frolov, V., Gautheron, F., Gavrichtchouk, O. P., Gerassimov, S., Giarra, J., Gnesi, I., Gorzellik, M., Grasso, A., Gridin, A., Grosse Perdekamp, M., Grube, B., Guskov, A., von Harrach, D., Heitz, R., Herrmann, F., Horikawa, N., d’Hose, N., Hsieh, C.-Y., Huber, S., Ishimoto, S., Ivanov, A., Iwata, T., Jandek, M., Jary, V., Joosten, R., Jörg, P., Kabuß, E., Kaspar, F., Kerbizi, A., Ketzer, B., Khaustov, G. V., Khokhlov, Yu. A., Kisselev, Yu, Klein, F., Koivuniemi, J. H., Kolosov, V. N., Kondo Horikawa, K., Konorov, I., Konstantinov, V. F., Kotzinian, A. M., Kouznetsov, O. M., Koval, A., Kral, Z., Krinner, F., Kulinich, Y., Kunne, F., Kurek, K., Kurjata, R. P., Kveton, A., Lavickova, K., Levorato, S., Lian, Y.-S.
• Format: Article
• Language: English
• Subjects: High Energy Physics - Experiment; High Energy Physics - Phenomenology; Physics
• ISSN: 0031-9007; 1079-7114
• DOI: 10.1103/PhysRevLett.127.082501

The COMPASS Collaboration experiment recently discovered a new isovector resonancelike signal with axial-vector quantum numbers, the a1 ( 1420 ) , decaying to f0 ( 980 ) π . With a mass too close to and a width smaller than the axial-vector ground state a1 ( 1260 ) , it was immediately interpreted as a new light exotic meson, similar to the X , Y , Z states in the hidden-charm sector. We show that a resonancelike signal fully matching the experimental data is produced by the decay of the a1 ( 1260 ) resonance into K* ( → Kπ ) K ¯ and subsequent rescattering through a triangle singularity into the coupled f0 ( 980 ) π channel. The amplitude for this process is calculated using a new approach based on dispersion relations. The triangle-singularity model is fitted to the partial-wave data of the COMPASS experiment. Despite having fewer parameters, this fit shows a slightly better quality than the one using a resonance hypothesis and thus eliminates the need for an additional resonance in order to describe the data. We thereby demonstrate for the first time in the light-meson sector that a resonancelike structure in the experimental data can be described by rescattering through a triangle singularity, providing evidence for a genuine three-body effect.