Ponente
Descripción
Mapping gluonic states in the light sector is a challenge,
and has led to controversies in the past. In particular, the experiments have reported two different states with exotic signature, \pi_1(1400) and \pi_1(1600), which couple separately
to \eta \pi and \eta' \pi. This picture is not compatible with the Lattice QCD estimates for hybrid states, nor with most phenomenological models.
We consider the most recent partial wave analysis of the \eta pi system performed by COMPASS. We fit it with a coupled-channel amplitude which 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 MeV and 492 +- 54 +- 102 MeV, which couples to both \eta(') pi channels. We find no evidence for a second exotic state. We also provide the resonant parameters of the a_2(1320) and a'_2(1700).
