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A few candidates exist, and whether they form the complete family predicted by lattice QCD is open.","posed_since":"","precise":"Lattice QCD predicts a lightest hybrid multiplet including a $J^{PC} = 1-+$ nonet between about $1.6\\text{ and }2.0\\ \\mathrm{GeV}$. Establish whether $\\pi1(1600)$ is the only isovector $1-+$ state below $2\\ \\mathrm{GeV}$ (a 2019 JPAC analysis described $\\pi1(1400)$ and $\\pi1(1600)$ as one pole), and whether $\\eta1(1855)$ (BESIII, 2022) and an isoscalar partner complete the nonet. Answer: masses, widths and decay patterns of the $1-+$ nonet members.","problem_ref":null,"references":"","settled_by":"Partial-wave analyses of GlueX photoproduction, COMPASS/AMBER pion-beam data and BESIII $J/\\psi$ decays establishing all members of the $1-+$ nonet.","status_note":"The single-pole pi1 interpretation (2019) and the eta1(1855) observation (2022) awaited independent confirmation as of 2026.","title":"Spectrum of light hybrid mesons with exotic quantum 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