Recent progress in the partial-wave analysis of the diffractively produced $\pi^-\pi^+\pi^-$ final state at COMPASS

TL;DR

This paper presents a novel freed-isobar partial-wave analysis of large COMPASS data, revealing complex dynamics in three-pion production and resolving mathematical ambiguities to gain deeper insight into meson interactions.

Contribution

It introduces a model-independent freed-isobar PWA approach to analyze diffractive three-pion production, addressing previous assumptions and resolving ambiguities in the analysis.

Findings

Resolved mathematical ambiguities in the PWA

Provided new insights into $2 o3$ meson dynamics

Analyzed spin-exotic wave $1^{-+}$ in detail

Abstract

The COMPASS spectrometer at CERN has collected a large data set for diffractive three-pion production of $46\times10^6$ exclusive events. Based on previous conventional Partial-Wave Analyses (PWA), we performed a `freed-isobar PWA' on the same data, removing model assumptions on the dynamic isobar amplitudes for dominating waves. In this analysis, we encountered continuous mathematical ambiguities, which we were able to identify and resolve. This analysis gives an unprecedented insight in the interplay of $2\pi$ and $3\pi$ dynamics in the process. As an example we show results for a spin-exotic wave $J^{PC}_{X^-}=1^{-+}$ wave.