Extraction of the light quark mass ratio from the decays psi' --> J/psi pi^0 (eta)

TL;DR

This paper investigates the extraction of the light quark mass ratio from psi' decays and finds that intermediate charmed meson loops significantly affect the decay processes, complicating precise measurements.

Contribution

The study demonstrates that intermediate charmed meson loops must be considered, challenging previous methods for determining the light quark mass ratio from these decays.

Findings

Charmed meson loops contribute significantly to psi' decays.

Decays are not suitable for precise quark mass ratio extraction.

Discrepancies in previous determinations are explained by loop effects.

Abstract

Light quark masses are important fundamental parameters of the Standard Model. The decays psi'-->J/psi pi^0 (eta) were widely used in determining the light quark mass ratio m_u/m_d. However, there is a large discrepancy between the resulting value of m_u/m_d and the one determined from the light pseudoscalar meson masses. Using the technique of non-relativistic effective field theory, we show that intermediate charmed meson loops lead to a sizeable contribution to the decays and hence make the psi'-->J/psi pi^0 (eta) decays not suitable for a precise extraction of the light quark mass ratio.