Fermi-Gamow-Teller Mixing in the Allowed Isospin-Hindered Positron Decay ofCo56

Abstract

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.