A measurement of K e vγ + decay

Abstract

The decay K + → e + vγ has been observed. In a counter experiment at CERN, 56 events of this type have been identified by detection of a γ with an energy > 100 MeV and of an e + with an energy between 236 MeV and the maximum e + energy, 247 MeV. The angle between γ and e + was > 120°. Thus, the experiment was sensitive only to the structure decay (SD) term proportional to the squared sum of vector- and axialvector amplitudes, | ν K + a K| 2, corresponding to the emission of right handed γ. We find Δ +(SD)/ Δ(K e2) = 1.05 −0.30 +0.25 and Δ_(SD) < 85 (90% CL). Δ + is in agreement with theoretical predictions.