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FAZZINI 1958

Fazzini, T.; Fidecaro, G.; Merrison, A.W.; Paul, H.; Tollestrup, A.V.;
Electron Decay of the Pion
Phys. Rev. Lett. 1 (1958) 247;

Motivation
It was predicted some years ago by Ruderman and Finkelstein that if the decay of the pion into an electron and a neutrino goes through an axial vector interaction, then it should occur at a rate 1.3 ´ 10^-4 of the normal decay into a muon and a neutrino. This conclusion has not been changed in the light of recent work on the nonconservation of parity in weak interactions. However, experiments by Lokanathan and Steinberger and by Anderson and Lattes failed to show the existence of the electron mode of decay. Interest has been revived in a search for this decay by the evidence for the validity of a universal Fermi interaction, which, with the single exception of the π e decay, is good. Theoretical attempts to remove this discrepancy have been made by a number of authors.
The experiment is made difficult by the presence of a large background of electrons from the π μ e chain of decay. However, these electrons can be distinguished in three ways. Firstly, they have a continuous spectrum with a maximum kinetic energy of 52.3 MeV, compared with the line spectrum of electrons from π e decay of 69.3 MeV. Secondly, the π e electrons should show a simple exponential decay with the mean life identical to that of the π μ decay, while the π μ e electron time distribution would show a two-stage radioactive decay, with a fast rise (approx. π μ mean life) and a slow fall (approx. μ e mean life). Lastly, three charged particles can be seen in the π μ e chain, while only two are shown in the π e decay.
We have used, like Lokanathan and Steinberger, a range telescope to search for the high energy π e electron. (Extracted from the introductory part of the paper.).

Accelerator CERN-SC Detectors CNTR

Related references
See also
M. A. Ruderman and R. J. Finkelstein, Phys. Rev. 76 (1949) 1458;
R. P. Feynman and M. Gell-Mann, Phys. Rev. 109 (1958) 193;
Analyse data from
S. Lokanathan and J. Steinberger, Nuovo Cim. Suppl. 2 (1955) 151;
H. L. Anderson and C. M. G. Lattes, Nuovo Cim. 6 (1957) 1356;

Reactions

	π+ e+ νe
	π– e– anti-νe

Particles studied

	π+	pw
	π–	pw

Record comments
First evidence for π_e2 decay.

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