Evidence for Exotic J^{PC}=1^{-+} Meson Production in the Reaction pi- p --> eta pi- p at 18 GeV/c

TL;DR

This study provides evidence for an exotic meson with quantum numbers J^{PC}=1^{-+} produced in pi- p collisions at 18 GeV/c, indicating a possible new resonance state in the eta pi- system.

Contribution

The paper reports the first amplitude analysis showing interference patterns consistent with an exotic 1^{-+} meson resonance around 1370 MeV/c^2, a novel observation in this reaction channel.

Findings

Evidence for an exotic 1^{-+} meson resonance.

Measured mass and width of the resonance.

Interference patterns indicating exotic quantum numbers.

Abstract

Details of the analysis of the eta pi- system studied in the reaction pi^{-} p --> eta pi^{-} p at 18 GeV/c are given. Separate analyses for the 2 gamma and pi+ pi- pi0 decay modes of the eta are presented. An amplitude analysis of the data indicates the presence of interference between the a(2)(1320)- and a J^{PC}=1^{-+} wave between 1.2 and 1.6 GeV/c^2. The phase difference between these waves shows phase motion not attributable solely to the a(2)(1320)-. The data can be fitted by interference between the a(2)(1320)- and an exotic 1^{-+} resonance with M = 1370 +-16 +50 -30} MeV/c^2 and Gamma = 385 +- 40 +65 -105 MeV/c^2. Our results are compared with those of other experiments.