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Radiative Σ± decays and search for neutral currents

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Zeitschrift für Physik

Abstract

The decay modesΣ ± ± γ, Σ +,Σ + →pe + e }- were studied in the 81 cm Saclay hydrogen bubble chamber. In the radiative decayΣ ± ± γ only low momentum pions which stop in the chamber were accepted.

We obtain the following branching ratios:

$$\frac{{\Gamma {\text{(}}\sum ^{\text{ + }} \to n\pi ^ + \gamma , p_{\pi + }^*< 110{\text{ MeV/c)}}}}{{\Gamma {\text{(}}\sum ^{\text{ + }} \to n\pi ^ + )}} = (2.7 \pm 0.5) \times 10^{ - 4} ,$$
((1))
$$\frac{{\Gamma {\text{(}}\sum ^ - \to n\pi ^ - \gamma , p_{\pi - }^*< 110{\text{ MeV/c)}}}}{{\Gamma {\text{(}}\sum ^ - \to n\pi ^ - )}} = (1.0 \pm 0.2) \times 10^{ - 4} ,$$
((2))
$$\frac{{\Gamma {\text{(}}\sum ^ + \to p\gamma {\text{)}}}}{{\Gamma {\text{(}}\sum ^ + \to p\pi ^0 )}} = (2.1 \pm 0.3) \times 10^{ - 3} ,$$
((3))
$$\frac{{\Gamma {\text{(}}\sum ^ + \to pe^ + e^ - {\text{)}}}}{{\Gamma {\text{(}}\sum ^ + \to p\pi ^0 )}} = (1.5 \pm 0.9) \times 10^{ - 5} .$$
((4))

The radiative branching ratios (1) and (2) agree well with theoretical calculations and confirm very strongly the assignmentS wave toΣ →nπ andP wave toΣ + + decay. The branching ratio (4) is based on 3 events with very low invariant masses of the electron-positron pair, being most probably radiative decays with internal conversion of theγ-ray. Combining (3) and (4) we obtain for the conversion coefficientρ:

in agreement with predictions from electrodynamics.

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Work partially supported by the Bundesministerium für Wissenschaftliche Forschung and IBM, Germany.

We wish to acknowledge the services of the CERN-Saclay bubble chamber crew in maintaining the fine operation conditions of the chamber. The ratio of stoppingK -mesons to background tracks depends very much on the manner in which the circulating PS-beam strikes the target. We wish to thank the PS crew for their excellent performance in this regard. We appreciate very much the efforts of our scanners who had to work under difficult conditions scanning photographs with a high number ofK-meson tracks. We are grateful to Drs. P. Lazeyras, P. Lexa, A. Minten, D. Plane, F. Wittgenstein and their collaborators for designing theK -beam. Without its excellent performance this experiment would not have been possible. We are indebted to H. Schleich for his invaluable assistance during the exposure of the film. We wish to thank Professors R. Armenteros, B. P. Gregory and Ch. Peyrou for their continuous support during the experiment. We thank Drs. M. Baggett and N. Baggett for a critical discussion.

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Ang, G., Ebenhöh, H., Eisele, F. et al. Radiative Σ± decays and search for neutral currents. Z. Physik 228, 151–162 (1969). https://doi.org/10.1007/BF01397536

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  • DOI: https://doi.org/10.1007/BF01397536

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