$1^{-+}$ exotic meson at light quark masses

TL;DR

This study investigates the mass of the $1^{-+}$ exotic meson at very light quark masses using lattice QCD, revealing a lower mass estimate consistent with experimental candidates and highlighting the importance of chiral effects.

Contribution

First lattice QCD study to explore $1^{-+}$ exotic meson mass at light quark masses near 25 MeV, showing significant curvature near the chiral limit.

Findings

$1^{-+}$ mass agrees with $ ext{pi}_1(1600)$ candidate

Significant curvature in mass near the chiral limit

Identified a $J^P=1^-$ state with mass close to 2 GeV

Abstract

The mass of the $1^{-+}$ exotic meson, created with hybrid interpolating fields, is explored at light quark masses approaching 25 MeV ($m_\pi / m_\rho \simeq 1/3$). Access to such light quark masses is facilitated by the use of the Fat-Link Irrelevant Clover (FLIC) fermion action. Additionally, we make use of large ($20^3 \times 40$) lattices to obtain good control of statistical and finite volume errors. Our results indicate that the $1^{-+}$ exotic exhibits significant curvature close the chiral limit, indicating previous linear extrapolations, far from the chiral regime, have overestimated the mass of the $1^{-+}$. We find for the first time in lattice studies a $1^{-+}$ mass in agreement with the $\pi_1 (1600)$ candidate. We also find a strangeness $\pm$1 $J^P = 1^-$ state with a mass close to 2 GeV.