Test of the multiquark structure of $a_1(1420)$ in strong two-body decays

TL;DR

This paper analyzes the strong two-body decays of the $a_1(1420)$ meson, exploring its possible four-quark structure and calculating decay modes to understand its nature and dominant decay channels.

Contribution

It investigates the four-quark configurations of $a_1(1420)$ and predicts dominant decay modes, providing insights into its internal structure compared to previous interpretations.

Findings

The dominant decay mode is $a_1 o K K^*$.

Decay modes $a_1 o VP$ account for the total width of about 150 MeV.

The $a_1 o f_0(980) + \pi^0$ decay is suppressed by an order of magnitude.

Abstract

We present an analysis of strong two-body decays of the $a_1(1420)$ with $J^{PC} = 1^{++}$ recently reported by the COMPASS Collaboration at CERN. Following the interpretation of the COMPASS Collaboration that the $a_1$ is an unusual state with a four-quark $q\bar q s \bar s$ structure we consider two possible configurations for this state --- hadronic molecular and color diquark-antidiquark structures. We find that the dominant decay mode of the $a_1$ is the decay into $K$ and $K^*$. In particular, we calculate that the four decay modes $a_1 \to VP$ with $VP = K^{*\pm}K^\mp$, $K^{*0}\bar K^0$, $\bar K^{*0}K^0$ together give a dominant contribution to the measured total width of about 150 MeV. The observational mode $a_1 \to f_0(980) + \pi^0$ is significantly suppressed by one order of magnitude.