Neutron Optics Parity and Time Reversal EXperiment : NOPTREX

What is Time Reversal Violation: In 1964 it was experimentally observed that combination of charge symmetry (C-symmetry) and parity symmetry (P-symmetry) is violated in decays of neutral kaons. This combined C- and P- symmetry is called CP-symmetry, and CP-symmetry breaking is called CP-violation. CP-violation was also observed in decay of neutral B decay, and D meson system.

In the framework of the CPT theorem, CP-violation indicates that time reversal symmetry (T-symmetry) is also violated. T-symmetry implies that replaying motion backward from the final state should bring the system to the time-reversed initial state (under time reversal, all particles are getting reversed to anti-particles and vice versa.

Why is that important: First of all, there is no fundamental explanation for the experimentally observed CP-violation. Secondly, Sakharov showed that CP-violation is necessary to produce matter-antimatter asymmetry in the Big Bang. However, the strength of T- (or CP-) violation is too small to explain matter-antimatter asymmetry. So, it would be important to find another experimental evidence of T-violation.

What is NOPTREX doing: The NOPTREX collaboration is working on measurement of T-violation in resonance neutron reactions with heavy nuclei.

Experiment is conducted with a polarized neutrons and polarized target. In 80s it was found, that parity (P-symmetry) is violated in resonance neutron reaction at much high rate, than expected by weak interaction. These enhancement is due to resonance nature of reaction between neutron and nuclei of the target. We expect that CP-symmetry breaking should experience the similar enhancement. There are two stages of the experiment:

What WKU group is working on: An experimentally observers T-violating effect is expected to be extremely small (at least 4 orders of magnitude smaller than weak interaction); hence, it is important

We are planning to participate in measurements at LANL and J-PARC and data analysis.