Measurement of the η-η' mixing angle in [π.sup.-] and [K.sup.-] beams with the GAMS-4π spectrometer

The η-η' mixing angle has been measured with the GAMS-4π spectrometer in a high statistics experiment. η' and η mesons were generated with charge-exchange reactions in 32.5 GeV/c [π.sup.-] and [K.sup.-] beams. Using both [π.sup.-] and K- beams allows the study of the |[η.sub.q]> and |[η.sub.s]> components of the meson wave function. The cross section ratio at t' = 0 [(GeV/c).sup.2] in the [π.sup.-] beam is [R.sub.π](η'/η) = 0.54 ± 0.04, and the mixing angle [φ.sub.P] = (36.3 ± 1.0)°.For the [K.sup.-] beam the ratio is [R.sub.K](η'/η) = 1.27 ± 0.15. It was found that the gluonium content in η' is [sin.sup.2] [φ.sub.G] = 0.17 ± 0.07.