On the nature of $a_1(1420)$

Abstract

The resonance-like signal with axial-vector quantum numbers $J^{PC}=1^{++}$ at a mass of $1420$MeV and a width of $140$MeV, recently observed by the COMPASS and VES experiments in the $f_0(980)\pi$ final state and tentatively called $a_1(1420)$, is discussed. Instead of a genuine new meson, we interpret this signal as a dynamical effect due to a singularity (branching point) in the triangle diagram formed by the processes $a_1(1260)\to K^{\star }\bar{K}$, $K^{\star }\to K\pi$, and $K\bar{K}\to f_0(980)$ (+ c.c). The amplitude for this diagram is calculated. The result exhibits a peak in the intensity with a sharp phase motion with respect to the dominant $a_1(1260)\to \rho \pi$ $S$-wave decay, in good agreement with the data. The branching ratio of $a_1(1260)\to f_0(980)\pi$ via the triangle diagram is estimated and compared to the dominant decay $a_1(1260)\to \rho \pi$.

28 pages, 8 figures

References in corpus (1)

• Glueballs, Hybrids, Multiquarks. Experimental facts versus QCD inspired concepts

Cited by in corpus (42)

• A Discussion on Triangle Singularities in the ${\Lambda }_b\to J/\psi K^{-}p$ Reaction
• Three-body Unitarity with Isobars Revisited
• The "$a_1(1420)$" peak as the $\pi f_0(980)$ decay mode of the $a_1(1260)$
• Light Baryon Spectroscopy
• Role of a triangle singularity in the $\gamma p\to K^{+}\Lambda (1405)$ reaction
• Novel approaches in Hadron Spectroscopy
• Revising the $f_1(1420)$ resonance
• Triangle singularity in the $J/\psi \to K^{+}{K}^{-}{f}_0(980)(a_0(980))$ decays
• How to understand the underlying structures of $X(4140)$, $X(4274)$, $X(4500)$ and $X(4700)$
• Triangular singularity and a possible $\varphi p$ resonance in the ${\Lambda }_c^{+}\to {\pi }^0\varphi p$ decay
• Triangle singularity mechanism for the $pp\to {\pi }^{+}d$ fusion reaction
• Triangle singularities in $B^{-}\to D^{\ast 0}{\pi }^{-}{\pi }^0\eta$ and $B^{-}\to D^{\ast 0}{\pi }^{-}{\pi }^{+}{\pi }^{-}$
• Abnormal isospin violation and $a_0-f_0$ mixing in the $D_s^{+}\to {\pi }^{+}{\pi }^0{a}_0(980)(f_0(980))$ reactions
• $f_2(1810)$ as a triangle singularity
• Test of the multiquark structure of $a_1(1420)$ in strong two-body decays
• Tetraquarks in holographic QCD
• Threshold effects as the origin of $Z_{cs}(4000)$, $Z_{cs}(4220)$ and $X(4700)$ observed in $B^{+}\to J/\psi \varphi K^{+}$
• Anomalous thresholds in $B\to (P,V){\gamma }^{\ast }$ form factors
• Bound states in the B-matrix formalism for the three-body scattering
• Comprehensive study of light axial vector mesons with the presence of triangle singularity
• Photo- and electro-production of narrow exotic states: from light quarks to charm and up to bottom
• Analysis of rescattering effects in $3\pi$ final states
• Unitarity, Analyticity and Crossing Symmetry in Two- and Three-hadron Final State Interactions
• Observation of a structure in the M${}_{p\eta }$ invariant mass distribution near 1700 MeV/$c^2$ in the $\gamma \mathbf{p}\to \mathbf{p}{\pi }^0\eta$ reaction
• Heating triangle singularities in heavy ion collisions
• Density of States of a Coupled-Channel System
• The vertex corrections due to the triangle singularity mechanism in the light axial vector meson couplings to $K^{\ast }\bar{K}+c.c.$
• Effects of Final State Interactions on Landau Singularities
• Detecting the pure triangle sigularity effect through the $\psi (2S)\to p\bar{p}\eta /p\bar{p}{\pi }^0$ process
• The $\pi f_0(500)$ decay of the $a_1(1260)$
• The role of triangle singularity in isospin breaking process $J/\psi \to \Lambda \bar{\Lambda }\pi$ and the possible evidence of ${\Sigma }^{\ast }({\frac{1}{2}}^{-})$ states
• Studying triangle singularity through spin observables
• $\Lambda (1405)$ mediated triangle singularity in the $K^{-}d\to p{\Sigma }^{-}$ reaction
• The role of triangle singularity in the decay process $D^0\to {\pi }^{+}{\pi }^{-}{f}_0(980),f_0\to {\pi }^{+}{\pi }^{-}$
• Partial wave analysis of ${\tau }^{-}\to {\pi }^{-}{\pi }^{+}{\pi }^{-}{\nu }_{\tau }$ at Belle
• Triangle mechanism in the decay process $B_0\to J/\psi K^0{f}_0(980)(a_0(980))$
• Spectroscopy of $a_1$ mesons from lattice QCD with the truncated overlap fermions
• Meson Spectroscopy at COMPASS
• The spectrum of light isovector mesons with $C=+1$ from the COMPASS experiment
• Box Singularity Conditions in Box Diagrams of Decay Processes
• Light-Meson Spectroscopy at COMPASS
• Measurement of the presence of ${\mathrm{a}}_1(1420)$ and $\omega (782)$ in ${\tau }^{-}\to {\pi }^{-}{\pi }^{-}{\pi }^{+}{\nu }_{\tau }$ at Belle