a High Statistics Study of Lambda Beta Decay.

A sample of 55,752 lambda beta decays has been detected in the Fermilab Neutral Hyperon Beam. A synchrotron radiation detector and a lead glass array together provided a rejection factor in excess of 10('4) against the non -leptonic lambda decay mode. The ratio of the axial vector to vector coupling constants in lambda beta decay has been determined. The values obtained are -0.757 (+OR-) 0.019 and +0.777 (+OR-) 0.019, where the errors are purely statistical. The systematic uncertainty presently assigned to each of these values is (+OR-)0.080; work is in progress to improve their accuracy. The branching ratio for lambda beta decay has also been measured. The result is (8.15 (+OR-) 0.69) x 10('-4), where the systematic uncertainty has been included in the error.