T-Violation Effects and Final-State Interactions

The difficulties connected with tests of time-reversal invariance are analyzed. We discuss the experimental situations in which $T$-violation effects are a priori forbidden on very general grounds, such as rotational invariance, etc. A rather detailed analysis is given of the effects of final-state interactions, which may in fact simulate $T$ violation. In particular, the case of $T$-odd correlations in scattering problems is discussed. Prescriptions are given on how to eliminate these spurious effects, or at least how to have them under control. The above techniques are discussed in the case of pion photoproduction in connection with the correlation ${\sigma }_N·{\mathrm{p}}_N\times {\mathrm{k}}_{\gamma }$. By suitably applying the above prescriptions, one may completely eliminate final-state-interaction effects and obtain a good test of $T$ violation with no spurious effects. The same general prescriptions are used in discussing $T$-violation effects in the processes $l+N\to l^{\prime }+\Gamma$.