Eta --> 3 pi and quark masses

TL;DR

This paper reviews the eta --> 3 pi decay process, highlighting its importance for determining light quark mass differences and addressing the challenges in understanding the Dalitz plot slope.

Contribution

It provides a comprehensive review of theoretical and experimental efforts related to eta decay and its implications for light quark mass differences.

Findings

Decay eta --> 3 pi helps determine (m_u - m_d)

Theory struggles to explain Dalitz plot slope

Experimental data on Dalitz plot is very precise

Abstract

In recent years, the decay eta --> 3 pi has received considerable attention from experimental and theoretical side. It is of particular theoretical interest because it allows for the determination of (m_u - m_d). In addition, for many years now theory has had difficulties to understand the slope of the neutral channel Dalitz plot distribution, which in contrast is very well measured. I discuss here the relation of the decay to the masses of the light quarks and review a number of theoretical and experimental works that are concerned with these questions.