Searching for time reversal invariance violation in polarized neutron decay

Time reversal invariance violation is tightly constrained in the Stan- dard Model, and the existence of a T-violating effect above the predicted level would be an indication of new physics. A sensitive probe of this symmetry in the weak interaction is the measurement of the D-coefficient in neutron decay. This parameter characterizes the triple-correlation of neutron spin, electron mo- mentum, and neutrino (or proton) momentum, which changes sign under time reversal. The emiT experiment, now on line, attempts to improve the measure- ment of D, whose current average is 0.3 + 1.5 x 10 -3.