We report a measurement of charge symmetry breaking in the NN η system. We have measured the ratio of the differential cross sections of the charge-symmetric reactions π+d→ nn η and π-d →+nn η in the energy region of the η threshold. Our result is R=dδ(π+d-→ppη)/dδ(π-nn η)= 0.938±0.009 after a phasespace correction is made for the difference in the threshold energies of the two reactions. The deviation of R from unity is an indication of charge symmetry breaking, which is mostly due to ir°- ij mixing. A theoretical model for 77 production which includes 77°- -q mixing was used to fit the data and yields a mixing angle of (1.5±0.4)°. Our result is consistent with the mixing angle determined in particle decay and isospin-forbidden processes as well as predictions by several theoretical analyses which yield = 1 °and another which yields ≈2°.
ASJC Scopus subject areas
- Physics and Astronomy (miscellaneous)