T-Invariance

T (or Time) invariance is a theory predicting that if a process is governed by a physical theory, then the same physical thoery applies in the reverse direction of time. C (or charge) invariance is the same principle when matter is replace by it's anit-matter counterpart. Lastly, there is P (or parity) invarianve which applies to a spacial inversion (i.e. the 3-D cartestion vector {x,y,z} becomes {-x,-y,-z}). When the three operations are all utilized on a system, then the TCP theorem indicates the system remains invariant.

However, with the discoveries of parity and CP violation in nuetral kaon decay (weak interaction), it became a question as whether time may not be invariant for other processes. T non-Invariance has been observed only in the weak decay of neutral kaons.

The study of this effect in the beta decay of nuetrons thus helps to give an insight as to the nature of symmetry breaking in physics. To date, a null value has been given to the D term, from the generalized beta decay formula derived by Jackson, Treiman, and Wyld in 1957, to the order of 10^(-3). This experiment proposes to improve measurement accuracy to one order greater via improvements in the techniques of polarization, detection and other areas.

The generalized formula for neutron beta decay is:

The D term is a triple product of the neutron spin, electron and antineutrino momentum. This is a T odd, P even term, thus resulting in a possible T non-Invariance effect if it is non-trivial. Else, if this term is zero, then neutron beta decay is T-Invariant.

Other techniques have been investigated to determine the value of the D term. One such technique is to mease whether or not the nuetron contains an Electric Dipole Moment (EDM). If the neutron had a permanent EDM, then upon different polarizations, the value of D would have different signs. Thus, by applying various magnetic pulses, this EDM would exhibit a precession and thus creating a measureable field of its own.