STUDY OF KE4 DECAYS

A study of 13.3×106 stopped K+ in a heavy-liquid bubble chamber yielded 269 Ke4 decays of the type e+π+π-ν, a total greater by a factor of 4 than the number found in a previous experiment. No examples of e-π+π+ν̄ were found. With 95% confidence, the upper limit for the decay rate of Ke4(e-) was found to be 56 sec-1. The rate for Ke4(e+) was found to be (2.60±0.30)×103 sec-1. The angular distributions and the dipion invariant-mass plot have been fitted by varying the form factors fs, fp, g, and h, and the difference between s- and p-wave π-π phase shift. Two acceptable solutions have been found. Both agree that the vector form factor h is significantly nonzero and that its sign is negative with respect to that of fg. Also, it has been found necessary to include fp in order to obtain a good fit. Although both solutions give the magnitude of the phase difference to be 25±9 deg, the two estimates have opposite sign. No evidence of a σ resonance is seen. The angular distributions are found to be consistent with time-reversal invariance, and with the locality of lepton production. © 1969 The American Physical Society.