1−+exotic meson at light quark masses

Abstract

The mass of the ${1}^{\ensuremath{-}+}$ exotic meson, created with hybrid interpolating fields, is explored in numerical simulations of quenched QCD on large (${20}^{3}\ifmmode\times\else\texttimes\fi{}40$) lattices to obtain good control of statistical and finite volume errors. Using the Fat-Link Irrelevant Clover (FLIC) fermion action, the properties of the ${1}^{\ensuremath{-}+}$ are investigated at light quark masses approaching 25 MeV (${m}_{\ensuremath{\pi}}/{m}_{\ensuremath{\rho}}\ensuremath{\simeq}1/3$). Under the standard assumption that the coupling to the quenched ${a}_{1}{\ensuremath{\eta}}^{\ensuremath{'}}$ channel comes with a negative metric, our results indicate that the ${1}^{\ensuremath{-}+}$ exotic exhibits significant curvature close to the chiral limit, suggesting previous linear extrapolations have overestimated the mass of the ${1}^{\ensuremath{-}+}$. We find for the first time in lattice studies a ${1}^{\ensuremath{-}+}$ mass consistent with the ${\ensuremath{\pi}}_{1}(1600)$ candidate. We also find a strangeness $\ifmmode\pm\else\textpm\fi{}1$ ${J}^{P}={1}^{\ensuremath{-}}$ state with a mass close to 2 GeV.