Amplitude analyses of the decays chi_c1 -> eta pi+ pi- and chi_c1 -> eta' pi+ pi-

TL;DR

This study performs amplitude analyses of chi_c1 decays to eta pi+ pi- and eta' pi+ pi-, revealing evidence for an exotic resonance and first observation of a specific decay mode, providing new insights into meson interactions.

Contribution

It reports the first observation of a_0(980) -> eta' pi decay and evidence for an exotic J^PC = 1^-+ resonance in eta' pi scattering.

Findings

Evidence for P-wave eta' pi scattering amplitude.

First observation of a_0(980) -> eta' pi decay.

Measured branching ratio B(a_0(980) -> eta' pi)/B(a_0(980) -> eta pi) = 0.064 +- 0.014 +- 0.014.

Abstract

Using a data sample of 2.59 x 10^7 psi(2S) decays obtained with the CLEO-c detector, we perform amplitude analyses of the complementary decay chains chi_c1 -> eta pi+ pi- and chi_c1 -> eta' pi+ pi-. We find evidence for a P-wave eta' pi scattering amplitude, which, if interpreted as a resonance, would have exotic J^PC = 1^-+ and parameters consistent with the pi_1(1600) state reported in other production mechanisms. We also make the first observation of the decay a_0(980) -> eta' pi and measure the ratio of branching fractions B(a_0(980) -> eta' pi)/B(a_0(980) -> eta pi) = 0.064 +- 0.014 +- 0.014. The pi pi spectrum produced with a recoiling eta is compared to that with eta' recoil.