Time-reversal noninvariance in nucleon-nucleon scattering. I. General formalism and zero-range parameterization

The observation that, in a time-irreversible one-boson-exchange nucleon-nucleon potential model due to Bryan and Gersten, T-violation occurs mostly in the lowest-permitted angular momentum states, leads us to construct a phase-shift parameterization of the 50 to 450 MeV NN data where T-violation takes place only in the lowest possible angular momentum states. The five ordinary (T-symmetric) Wolfenstein amplitudes are taken from phase shift analysis, and the sixth, T-asymmetric amplitude, t(θ), is parameterized by a single infinitesimal phase parameter λ₁(λ₂) in the case of np(pp) scattering. This leads to unique predictions for the relative angular distributions of time-reversal-asymmetric observables P - a and P_A - P_B, even though the absolute magnitudes remain undetermined. The model corresponds to an ordinary interaction that yields the usual experimental data, plus a superimposed very short-range T-noninvariant force. As such, it directs experimentalists to those angular regions of pp and np P - a and P_A - P_B measurements where T-violation due to short-range forces will be most strongly manifest. As the model incorporates isospin invariance, known to hold only at the few-percent level in np scattering, the predictions are likely to have greater significance in the case of pp scattering.