Determination of low-energy parameters of neutron--neutron scattering from an analysis of the binding-energy difference between the [sup.3]H and [sup.3]He mirror nuclei

A relation between quantities that characterize the breaking of the charge symmetry of nuclear forces in systems of two and three nucleons is found on the basis of an analysis of the binding-energy difference between the [sup.3]Hand [sup.3]He mirror nuclei. For the neutron-neutron scattering length and effective range, the values of [a.sub.nn] = -18.38(55) fm and [r.sub.nn] =2.84(4) fm, respectively, were obtained by using purely nuclear parameters of proton--proton scattering in the [sup.1][S.sub.0] state. The calculated values agree with present-day experimental results.