Test of time reversal invariance in 2-MeV neutron scattering from aligned165Ho

We describe a search for the time reversal non-invariant five-fold correlation (s·Ixk)(I·k) in the scattering of 2 MeV polarized neutrons from an aligned165Ho target. Here s is the neutron spin,I is the target spin, andk is the neutron momentum vector. Differences in transmission were sought when s was reversed. The target was a single crystal of holmium, cryogenically aligned with a specially built dilution refrigerator. Rotating the target axis of alignment while cold permits the parity-even, five-fold correlation to be identified among other spin-dependent correlations in the forward elastic scattering amplitude. An analyzing power was found to be (1±6)×10−4, consistent with time reversal invariance.We obtain a bound of 5×10−3 for αT, the ratio of T-odd to T-even couplings in the effective nucleon-nucleon interaction.