Eta --> 3 pi and quark masses

Understand

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.