Measurement of Gamma(phi -> eta' gamma)/Gamma(phi -> eta gamma) and the pseudoscalar mixing angle

TL;DR

This paper reports a precise measurement of the ratio of decay widths for phi mesons into eta' gamma and eta gamma, leading to improved estimates of the pseudoscalar mixing angle.

Contribution

The study provides the first precise measurement of the decay width ratio and the pseudoscalar mixing angle using a large phi meson sample at DAFNE.

Findings

Measured decay width ratio: (4.70 +- 0.47 +- 0.31) x 10^-3

Derived branching ratio for phi -> eta' gamma: (6.10 +- 0.61 +- 0.43) x 10^-5

Estimated pseudoscalar mixing angle: (41.8 +1.9 -1.6) degrees

Abstract

We have measured the radiative decays phi -> eta gamma, phi ->etaprime gamma selecting pi+ pi- gamma gamma gamma final state in a sample of about 5 times 10^7 phi mesons produced at the Frascati phi factory DAFNE. We obtain Gamma(phi -> etaprime gamma)/Gamma(phi -> eta gamma)=(4.70 +- 0.47 +- 0.31) times 10^-3. From this result we derive new accurate values for the branching ratio BR(phi ->etaprime gamma) = (6.10 +- 0.61 +- 0.43) times 10^-5, and the mixing angle of pseudoscalar mesons in the flavour basis phi_P=(41.8 +1.9 -1.6) degrees.