No abstract

The asymmetry parameter, 2 p, in the positron decay of polarized "Co has been measured to be +0.341+0.013. Assuming the standard T-invariant V -A weak interaction theory, the Fermi to Gamow-Teller mixing ratio, y =Cl MF/CzMzT, was determined to be -0.005+0.008. The vanishing value of y is consistent with the isospin selection rule for the Fermi matrix element. RADIOACTIVITY "Co; measured P(9), y(()); deduced source P, P asymmetry coefficient, Fermi to Gamow-Teller mixing ratio.

calculated effective decay lengths agree within about 0.2 mm. Variations of the above control sample were also studied. Considering the consistency of all the data for both T and control events we have assigned a systematic uncertainty of 0.3 mm to the decay path measurement.Taking the T mass to be 3 1.782 GeV, and the average beam energy for this experiment of 14.5 GeV, we find for the lifetime T T =(4.9±2.0)X10" 13 sec.A new high-precision measurement of the asymmetry coefficient, A$ 9 for the positron decay of polarized 56 Co is reported: A^ = + 0.359± 0.009. If one assumes the V-A form of the weak interaction and time-reversal invariance, the Fermi-Gamow-Teller mixing ratio, y = C V M ¥ /C A M GT9 is then -0.091 ± 0.005. Since y is nonzero and isospin is not conserved, 56 Co (3 + decay is a good candidate for sensitive time-reversal invariance tests of the weak interaction.