Check of T Invariance in Electromagnetic Interaction

An apparent violation of time‐reversal invariance in the electromagnetic interaction was reported at the New York American Physical Society meeting by David Bartlett, K. Goulianos, Carl Friedberg, Ira Hammerman and David Hutchinson of Princeton. The group compared angular distributions for $n+p→γ+d$ with data from other sources on the inverse reaction $γ+d→n+p$ to test reciprocity and hence check time‐reversal invariance. In the experiment, neutron energies from 160 to 680 MeV were studied. At lower values of energy the angular distributions for both of the reactions matched. But at about 600 MeV, which corresponds to formation of the $N*$ resonance, the curves did not match. Michael Longo (University of Michigan) and his collaborators in a similar experiment do not see the large effect reported by the Princeton experimenters. Although many particle physicists are excited about the observations, a typical attitude is, “Interesting if true.”