# Determination of the Pole Position of the Lightest Hybrid Meson Candidate

Rodas, A. (Departamento de Física Teórica, Universidad Complutense de Madrid, E-28040 Madrid, Spain) ; Pilloni, A. (Theory Center, Thomas Jefferson National Accelerator Facility, Newport News, VA 23606, USA) (European Centre for Theoretical Studies in Nuclear Physics and Related Areas (ECT*) and Fondazione Bruno Kessler, I-38123 Villazzano (TN), Italy) ; Albaladejo, M. (Theory Center, Thomas Jefferson National Accelerator Facility, Newport News, VA 23606, USA) (Departamento de Física, Universidad de Murcia, E-30071 Murcia, Spain) ; Fernández-Ramírez, C. (Instituto de Ciencias Nucleares, Universidad Nacional Autónoma de México, Ciudad de México 04510, Mexico) ; Jackura, A. (Center for Exploration of Energy and Matter, Indiana University, Bloomington, IN 47403, USA) (Physics Department, Indiana University, Bloomington, IN 47405, USA) ; Mathieu, V. (Theory Center, Thomas Jefferson National Accelerator Facility, Newport News, VA 23606, USA) ; Mikhasenko, M. (Universität Bonn, Helmholtz-Institut für Strahlen- und Kernphysik, 53115 Bonn, Germany) ; Nys, J. (Department of Physics and Astronomy, Ghent University, Ghent 9000, Belgium) ; Pauk, V. (Institut für Kernphysik & PRISMA Cluster of Excellence, Johannes Gutenberg Universität, D-55099 Mainz, Germany) ; Ketzer, B. (Universität Bonn, Helmholtz-Institut für Strahlen- und Kernphysik, 53115 Bonn, Germany) ; Szczepaniak, A. P. (Theory Center, Thomas Jefferson National Accelerator Facility, Newport News, VA 23606, USA) (Center for Exploration of Energy and Matter, Indiana University, Bloomington, IN 47403, USA) (Physics Department, Indiana University, Bloomington, IN 47405, USA)

29 January 2019

Abstract: 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, ${\pi }_{1}\left(1400\right)$ and ${\pi }_{1}\left(1600\right)$, which couple separately to $\eta \pi$ and ${\eta }^{\prime }\pi$. 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 ${\eta }^{\left(\prime \right)}\pi$ 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 ${\pi }_{1}$ resonant pole, with mass and width $1564±24±86$ and $492±54±102\text{}\text{}\mathrm{MeV}$, which couples to both ${\eta }^{\left(\prime \right)}\pi$ channels. We find no evidence for a second exotic state. We also provide the resonance parameters of the ${a}_{2}\left(1320\right)$ and ${a}_{2}^{\prime }\left(1700\right)$.

Published in: Physical Review Letters 122 (2019)