Triangle Singularity as the Origin of the a1 (1420)

0549444 - ÚPT 2022 RIV US eng J - Journal Article
Alexeev, G. D. - Alexeev, M. - Amoroso, A. - Andrieux, V. - Anosov, V. - Antoshkin, A. - Augsten, K. - Augustyniak, W. - Azevedo, C. D. R. - Badelek, B. - Balestra, F. - Ball, M. - Barth, J. - Beck, R. - Bedfer, Y. - Antequera, J. B. - Bernhard, J. - Bodlák, M. - Bradamante, F. (ed.) - 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. - Srnka, Aleš … Total 198 authors
Triangle Singularity as the Origin of the a1 (1420).
Physical Review Letters. Roč. 127, č. 8 (2021), č. článku 082501. ISSN 0031-9007. E-ISSN 1079-7114
Institutional support: RVO:68081731
Keywords : meson muoproduction * liquid hydrogen target * generalised parton distributions
OECD category: Particles and field physics
Impact factor: 9.185, year: 2021
Method of publishing: Open access
https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.127.082501

The COMPASS Collaboration experiment recently discovered a new isovector resonancelike signal with axial-vector quantum numbers, the a(1)(1420), decaying to f(0)(980)(pi). With a mass too close to and a width smaller than the axial-vector ground state a(1)(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 a(1) (1260) resonance into K* (-> K pi) (K) over bar and subsequent rescattering through a triangle singularity into the coupled f(0)(980)p 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 lightmeson 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.
Permanent Link: http://hdl.handle.net/11104/0325472