arxiv: 2006.05342 · v3 · ★pith:SJYUQJT7new · submitted 2020-06-09 · ✦ hep-ph · hep-ex
Triangle Singularity as the Origin of the a₁(1420)
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The COMPASS experiment recently discovered a new isovector resonance-like 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 resonance-like signal fully matching the experimental data is produced by the decay of the $a_1(1260)$ resonance into $K^\ast(\to K\pi)\bar{K}$ and subsequent rescattering through a triangle singularity into the coupled $f_0(980)\pi$ 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 less 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 resonance-like structure in the experimental data can be described by rescattering through a triangle singularity, providing evidence for a genuine three-body effect.
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Cited by 2 Pith papers
Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score.
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The $a_1(1420)$ in a Unitary Coupled-Channel Three-Body Approach
hep-ph 2026-06 unverdicted novelty 5.0
Unitary coupled-channel three-body model fitted to COMPASS data reproduces the a1(1420) enhancement via triangle singularity, indicating no genuine resonance pole is required.
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Effects of Final State Interactions on Landau Singularities
hep-ph 2024-07 unverdicted novelty 5.0
Triangle singularities mimicking resonances are analyzed in the presence of final-state rescattering using Landau equations and a scattering formalism enforcing two- and three-body unitarity.
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