# Recent results on light-meson exotics from COMPASS experiment

- Institution: CERN
- Department: EP Seminar
- Speaker: Mikhail Mikhasenko
- Year: 2021
- Language: English
- Source: [CERN](https://videos.cern.ch/record/3014485)
- Licence: [CERN](http://copyright.web.cern.ch)
- Who can watch: Teens profiles and older (sources give no ratings; placed by Invisible Network from the source's own words)

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

seen in the $f_0(980)\pi$ system is produced by such a triangle

singularity, which causes the particles produced in the collision to

change their identities via mutual interaction right at the interaction

point.

I will demonstrate how progress in the understanding of the strong

interaction benefits from a tight collaboration between theory and

experiment on the example of the cooperation of the COMPASS experiment

and the Joint Physics Analysis Center (JPAC).

EP seminar 27 July: https://cern.zoom.us/j/64131202472?pwd=Mk5MWUxQWjF3UkVxdzl1WUFQU1FVQT09.

0:00:00 Slide 1

0:06:09 Slide 2

0:12:18 Slide 3

0:18:27 Slide 4

0:24:36 Slide 5

0:30:45 Slide 6

0:36:53 Slide 7

0:43:02 Slide 8

0:49:11 Slide 9

0:55:20 Slide 10

1:01:29 Slide 11

## Lectures

1. [Recent results on light-meson exotics from COMPASS experiment](https://invisiblenetwork.ai/learn/cern/3014485/d810320d8153), 1 h 2 min (CERN's player)