Recent results on light-meson exotics from COMPASS experiment

About

The talk will discuss two prime candidates for exotic hadrons in the

light-meson sector: the hybrid candidate $\pi_1(1600)$ with manifestly

non-$q\bar{q}$ quantum numbers, $J^{PC}=1^{-+}$, and the tetraquark

candidate $a_1(1420)$ located in the vicinity of the $K^*\bar{K}$ threshold.

Based on high-precision data from the COMPASS experiment at CERN, we

observe the $\pi_1(1600)$ hybrid candidate as a resonance in the

$\rho(770)\pi$ and $\eta^\prime\pi$ systems. Moreover, our studies bring

a long-awaited understanding of the seemingly contradictory claims made

in previous analyses of the $\rho(770)\pi\,P$ partial wave.

Studying the tetraquark candidate $a_1(1420)$, we find evidence for a

so-called triangle singularity, a much sought-after effect of the strong

interaction. Our new analysis suggests that the resonance-like signal