Departamento de Física Teórica, Universidad Complutense de Madrid, E-28040 Madrid, Spain.
Theory Center, Thomas Jefferson National Accelerator Facility, Newport News, VA 23606, USA.
Phys Rev Lett. 2019 Feb 1;122(4):042002. doi: 10.1103/PhysRevLett.122.042002.
Mapping states with explicit gluonic degrees of freedom in the light sector is a challenge, and has led to controversies in the past. In particular, the experiments have reported two different hybrid candidates with spin-exotic signature, π_{1}(1400) and π_{1}(1600), which couple separately to ηπ and η^{'}π. This picture is not compatible with recent Lattice QCD estimates for hybrid states, nor with most phenomenological models. We consider the recent partial wave analysis of the η^{(')}π system by the COMPASS Collaboration. We fit the extracted intensities and phases with a coupled-channel amplitude that enforces the unitarity and analyticity of the S matrix. We provide a robust extraction of a single exotic π_{1} resonant pole, with mass and width 1564±24±86 and 492±54±102 MeV, which couples to both η^{(')}π channels. We find no evidence for a second exotic state. We also provide the resonance parameters of the a_{2}(1320) and a_{2}^{'}(1700).
在光区域中明确具有胶子自由度的状态映射是一项挑战，过去曾引发争议。特别是，实验报告了两个具有自旋奇特特征的不同混合候选体，π_{1}(1400)和π_{1}(1600)，它们分别与ηπ和η^{'}π耦合。这种情况与最近的格点 QCD 对混合态的估计以及大多数唯象模型都不兼容。我们考虑了 COMPASS 合作最近对 η^{(')}π 系统的部分波分析。我们用一个耦合通道振幅来拟合提取的强度和相位，该振幅强制 S 矩阵的幺正性和解析性。我们提供了一个独特的奇异π_{1}共振极点的稳健提取，其质量和宽度为 1564±24±86 和 492±54±102 MeV，它与两个 η^{(')}π 通道耦合。我们没有发现第二个奇异态的证据。我们还提供了 a_{2}(1320)和 a_{2}^{'}(1700)的共振参数。
