Determination of the Pole Position of the Lightest Hybrid Meson Candidate

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, π1(1400) and π1 (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 π1 resonant pole, with mass and width 1564 ± 24 ± 86 MeV 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 a2(1320) and a 2 (1700).

η′ and η mesons with connection to anomalous glue

“…No enhancement was observed in the even L partial waves. For further recent discussion, see also Rodas et al (2017).…”

Moments of angular distribution and beam asymmetries in ηπ0 photoproduction at GlueX

“…In order to reduce the number of projections, we can use the empirical observation of s-channel helicity conservation [8,14]. 2 Fortunately, observables (moments and beam asymmetries) extracted in the helicity frame can be computed in the s-channel frame. As illustrated in Fig.…”

“…m R and Γ R are the masses and total widths of the resonance R respectively. For the π 1 (1600), a 2 (1320) and a 2 (1700) resonances, we use the mass and width obtained from a recent fit to the π − p → η ( ) π − p COMPASS data [2]. For the a 0 , we use the average mass and width quoted in the Review of Particle Physics [15].…”

Hybrid Meson Interpretation of the Exotic Resonance π11600

“…Even though they saw the exotic 1 −+ wave in η ′ π as the dominant wave, they were unable to confirm the resonant nature of the signal [44]. This has recently been improved by the JPAC collaboration [45] which performed the first coupled-channel analysis of the P-wave in the η ð ′ Þ π system measured at COMPASS [44] and reported a single exotic π 1 with mass and width determined to be 1564 ± 24 ± 86 and 492 ± 54 ± 102 MeV, respectively.…”