Test of the ΔS = ΔQ Rule and CP-Invariance in $K_{e3}$ Decay

Abstract

The complex quantity X = (amplitude of the ΔS = -ΔQ process K-o → π-e+v/amplitude of the ΔS = +ΔQ process Ko → π-e+v) has been measured in a counter-spark-chamber experiment at the LRL Bevatron. Assuming CPT invariance, ImX ≠ 0 implies CP-violation in the decay. Ko - mesons were produced in two brass targets by 2.85 GeV/c pions. A series of veto counters and hodoscopes selected neutral decays into two charged particles. The electron and pion were identified by (1) pulse height in a Freon 12 threshold Cerenkov counter, (2) visual appearance in three radiation lengths of lead, and (3) pulse height in a set of fourteen shower counters. From 240K pictures, 1,079 events were isolated with a (2 ± 1)% background level. A maximum likelihood fit to the π-e+ and +e- time distributions gave the result: ReX = -.069 ± .036 ImX = +.108 ± +.092-.074 This result is within two standard deviations of X = 0 and therefore consistent with it (relative probability = 0.25). It is, on the other hand, more than four standard deviations from the existing world average (+0.14, -0.13) and therefore inconsistent with it (relative probability < 3.3 x 10-4). Sensitivity of the result to a large number of possible systematic effects was investigated and it was concluded that any systematic error was small compared to the statistical error.