An experimental test of parity‐even time reversal invariance with MeV neutrons

A new measurement of the parity‐conserving, time reversal noninvariant (PC TRNI) fivefold correlation has been performed at Triangle Universities Nuclear Laboratory, using 6.57 MeV polarized neutrons and a cryogenically aligned holmium target. The PC TRNI spin correlation coefficient A5 is measured to be (1.1±2.3)×10−5, consistent with time reversal invariance. A bound of 3.8×10−3 (99% confidence) is extracted for the ratio of PC TRNI to TRI nuclear matrix elements.