Decay properties of light 1−+ hybrids

Abstract

We explore the decay properties of the isovector and isoscalar 1⁻⁺ light hybrids, π₁ and η₁, in N_f = 2 lattice QCD at a pion mass m_π ≈ 417 MeV. The McNeile and Michael method is adopted to extract the effective couplings for individual decay modes, which are used to estimate the partial decay widths of π₁(1600) and η₁(1855) by assuming SU(3) symmetry. The partial decay widths of π₁(1600) are predicted to be \((\Gamma_{b1\pi}, \Gamma_{f1(1285)\pi}, \Gamma_{\rho \pi}, \Gamma_{K* \bar{K}})=(325\pm75, \mathcal{O}(10),52\pm7,8.6\pm1.3)\) MeV, and the total width is estimated to be 396 ± 90 MeV, considering only statistical errors. If η₁(1855) and the 4.4σ signal observed by BESIII (labeled as η₁(2200)) are taken as the two mass eigenstates of the isoscalar 1⁻⁺ light hybrids in SU(3), then the dominant decay channel(s) of η₁(1855) (η₁(2200)) is \(K_{1}(1270)\bar{K}\ (K_{1}(1270)\bar{K}\) and \(K_{1}(1400)\bar{K}\) through the 1⁺⁽⁻⁾0⁻⁽⁺⁾ mode. The vector-vector decay modes are also significant for the two η₁ states. Using the mixing angle α ≈ 22.7° obtained from lattice QCD for the two η₁ states, the total widths are estimated to be \(\Gamma_{\eta1(1855)} = 282(85)\) MeV and \(\Gamma_{\eta1(2200)} = 455(143)\) MeV. The former is compatible with the experimental width of η₁(1855). Although many systematic uncertainties are not well controlled, these results are qualitatively informative for the experimental search for light hybrids.