engleski

Measurement of Charge Symmetry Breaking by the Comparison of Pi^+d->p p Eta with Pi^-d->n n Eta

We report a measurement of charge symmetry breaking in the NN Eta system. We have measured the ratio of the differential cross sections of the charge-symmetric reactions Pi^+d->p p Eta with Pi^-d->n n Eta in the energy region of the Eta threshold. Our result is R=d Sigma(Pi^+d->ppEta)/d Sigma(Pi^-d->nn Eta)=0.938+-0.009 after a phase-space 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 Pi^0 - Eta mixing. A theoretical model for Eta production which includes Pi^0 - Eta mixing was used to fit the data and yields a mixing angle of (1.5+-0.4)^o. 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^o and another which yields ~ 2^o.

charge symmetry breaking ; NN Ni system ; differential cross section

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