Exotic Meson Production in the $f_{1}(1285)\pi^{-}$ System observed in the Reaction $\pi^{-} p \to \eta\pi^{+}\pi^{-}\pi^{-} p$ at 18 GeV/c

TL;DR

This study uses partial wave analysis to identify and characterize exotic mesons with quantum numbers $J^{PC} = 1^{-+}$ in $ o f_{1}(1285)\pi^{-}$ decay channels, revealing new and known resonances consistent with hybrid meson models.

Contribution

First observation of an exotic $1^{-+}$ meson in the $f_{1}(1285)\pi^{-}$ system with detailed resonance parameters and confirmation of related states, supporting hybrid meson theories.

Findings

Evidence for two $1^{-+}$ mesons with specific masses and widths.

Confirmation of $ ext{π}_2(1900)$ resonance.

Discovery of a new $a_1(2096)$ state.

Abstract

This letter reports results from the partial wave analysis of the $\pi^{-}\pi^{-}\pi^{+}\eta$ final state in $\pi^{-}p$ collisions at 18GeV/c. Strong evidence is observed for production of two mesons with exotic quantum numbers of spin, parity and charge conjugation, $J^{PC} = 1^{-+}$ in the decay channel $f_{1}(1285)\pi^{-}$. The mass $M = 1709 \pm 24 \pm 41$ MeV/c^2 and width $\Gamma = 403 \pm 80 \pm 115$ MeV/c^2 of the first state are consistent with the parameters of the previously observed $\pi_{1}(1600)$. The second resonance with mass $M = 2001 \pm 30 \pm 92$ MeV/c^2 and width $\Gamma = 333 \pm 52 \pm 49$ MeV/c^2 agrees very well with predictions from theoretical models. In addition, the presence of $\pi_{2}(1900)$ is confirmed with mass $M = 2003 \pm 88 \pm 148$ MeV/c^2 and width $\Gamma = 306 \pm 132 \pm 121$ MeV/c^2 and a new state, $a_{1}(2096)$, is observed with mass $M = 2096 \pm 17 \pm 121$ MeV/c^2 and width $\Gamma = 451 \pm 41 \pm 81$ MeV/c^2. The decay properties of these last two states are consistent with flux tube model predictions for hybrid mesons with non-exotic quantum numbers.