# Resonance a_1(1420) and the Three-Pion Decays of the Tauon

## TL;DR

This study investigates the role of the a_1(1420) resonance in tau lepton decays to three pions, suggesting it may be the primary axial-vector resonance involved, based on recent data analysis.

## Contribution

The paper provides evidence that the a_1(1420) resonance, rather than the traditionally assumed a_1(1640), is the main axial-vector resonance in tau three-pion decays, based on phenomenological modeling and data analysis.

## Key findings

- Recent data favor a_1(1420) over a_1(1640)
- a_1(1420) likely the main resonance in tau decays
- More data needed for definitive conclusion

## Abstract

The role of the a_1(1420) resonance in the three-pion decays of the tau lepton is investigated using a phenomenological model. For all data before 2008, roughly equal fit quality is achieved when the basic a_1(1260) resonance is supplemented with either a_1(1640) or a_1(1420). However, two recent and more precise data sets require resonances with masses that are not very far from that of a_1(1420). This suggests that the axial-vector resonance that accompanies the a_1(1260) in the three-pion decays of the tauon is a_1(1420), not a_1(1640), as believed up to now. More data are needed to demonstrate this definitely.