Convergence properties of $\eta\to 3\pi$ decays in chiral perturbation theory

TL;DR

This paper investigates the convergence of chiral perturbation theory in describing $ ext{η} o 3 ext{π}$ decays, showing that experimental data can be compatible with reasonable theoretical assumptions, despite some tensions in specific parameters.

Contribution

It applies resummed chiral perturbation theory with statistical treatment of uncertainties to analyze decay widths and Dalitz plot parameters, providing new insights into convergence issues.

Findings

Decay widths align with experimental data under certain parameter ranges.

Dalitz plot parameters a and d are well described by the model.

Mild tension exists for parameters b and α, less than 2σ confidence level.

Abstract

Theoretical efforts to describe and explain the $\eta\to 3\pi$ decays reach far back in time. Even today, the convergence of the decay widths and some of the Dalitz plot parameters seems problematic in low energy QCD. In the framework of resummed CHPT, we explore the question of compatibility of experimental data with a reasonable convergence of a carefully defined chiral series, where NNLO remainders are assumed to be small. By treating the uncertainties in the higher orders statistically, we numerically generate a large set of theoretical predictions, which are then confronted with experimental information. In the case of the decay widths, the experimental values can be reconstructed for a reasonable range of the free parameters and thus no tension is observed, in spite of what some of the traditional calculations suggest. The Dalitz plot parameters $a$ and $d$ can be described very well too. When the parameters $b$ and $\alpha$ are concerned, we find a mild tension for the whole range of the free parameters, at less than 2$\sigma$ C.L. This can be interpreted in two ways - either some of the higher order corrections are indeed unexpectedly large or there is a specific configuration of the remainders, which is, however, not completely improbable. Also, the distribution of the theoretical uncertainties is found to be significantly non-gaussian, so the consistency cannot be simply judged by the 1$\sigma$ error bars.