Is the Up Quark Massless?

TL;DR

This paper uses lattice calculations to evaluate low energy constants in the chiral Lagrangian, providing evidence against the up quark being massless by analyzing the critical combination 2α8−α5.

Contribution

It presents new lattice calculation results for the combination 2α8−α5, challenging the hypothesis of a massless up quark.

Findings

2α8−α5 = 0.115 ± 0.051 (stat) ± 0.25 (syst)

Result is outside the range compatible with a massless up quark

Supports the non-zero mass of the up quark

Abstract

Several lattice calculations of a combination of the low energy constants of the chiral Lagrangian, 2\alpha_8-\alpha_5, are presented. This combination is critical for the preclusion of a massless up quark. The result found is 2\alpha_8-\alpha_5 = 0.115 \pm 0.051^{stat} \pm 0.25^{syst}, which is well outside of the range allowed by a massless up quark.