Search

New measurements of baryon leptonic decay rates and formfactor ratios make a new comparison with the Cabibbo theory desirable. The data are consistent with the one angle Cabibbo theory, the results for the three free parameters are: Θ=0.239±0.006, g=0.488±0.020, g=0.743±0.020. [ABSTRACT FROM AUTHOR]

The ratio of the axial-vector to vector coupling constant, ¦ g/ f¦, in the Σ→ ne $$\bar v$$ decay was determined from the electron-neutrino angular distribution. In a sample of 454 Σ→ ne $$\bar v$$ decays a search was made for subsequent neutron proton scattering in order to detect the decay neutrons. The Σ hyperons were produced by stopping K-mesons in the 81 cm Saclay hydrogen bubble chamber. For the kinematical analysis 33 Σ→ ne ν events with associated np→np interactions were accepted. The value ¦ g/ f¦=0.37 was obtained. [ABSTRACT FROM AUTHOR]

Approximately 10 Σ decays of the stopping K film (80 cm Saclay HBC) have been measured with the Heidelberg KONRAD-system. This system is capable of detecting about 75% of the Σ→ ne¯ v decays. In addition, about 10 pictures have been scanned for Σ leptonic decays with secondary particle momenta below 80 MeV/c. This covers about 15% of the lepton spectrum. The data yield the following branching ratios: Since only a part of the lepton spectra is detected, the branching ratios depend slightly on the form of the transition matrix elements. The values quoted above were derived taking the Cabibbo solution g/f=−0.24 and the CVC prediction f/f=−1.14. The branching ratios are in good agreement with μ, e universality. [ABSTRACT FROM AUTHOR]

In a sample of 10 Σ hyperons we have searched for the decays σ→ ne ν and σ→ nμ ν, which would violate the ΔQ=ΔS rule. No Σ→ne ν decay was found, whereas 313 σ→ne ν decays were identified in the same film. With 90% confidence we obtain Having found two candidates for the decay σ→ nμ ν and 104 Σ→ nμ ν events we obtain for the muonic mode The probability that the μ-events are simulated by σ→ nπ γ with subsequent undetected π→ μ ν decay is less than 4%. [ABSTRACT FROM AUTHOR]

From about 6×10 stopping K-meson reactions in the Saclay 80 cm hydrogen bubble chamber 70 Σ→Λe¯ν and 11Σ→Λeν decays have been identified. The ratio of the vector to axial vector coupling constant has been determined, f/ g=−0.22±0.28, consistent with the prediction f=0 of the CVC-theory. The branching ratios for the two decay modes are, Γ( Σ→Λeν)/Γ(Σ→ all modes)=(0.69±0.12). 10, Γ(Σ→Λeν)/Γ(Σ→ all modes)=(0.29±0.10). 10. The ratio, Γ(Σ→Λe)/Γ(Σ→Λev)=0.69±0.18, agrees with the phase space ratio, 0.61, therefore a theory that includes no second class currents is consistent with the data. [ABSTRACT FROM AUTHOR]

The two ∑ reactions at rest ∑ p→ Λ n and ∑ p→ Λ n have been studied in order to determine the capture ratio, the Λ-lifetime and the ∑- Λ mass difference. The following results were obtained: The ∑-mass was determined from the range of the stopping ∑-hyperons, M=1197.19±0.32 MeV/ c. [ABSTRACT FROM AUTHOR]

We have found a possible example of the rare decay σ →nΜ Ν, which violates δS=δQ. The positive decay track of the σ comes to rest in the hydrogen bubble chamber and decays into an e. This track has all the characteristics of a stopping Μ. The decay neutron fortuitously scatters twice, producing two recoil protons. The only other possible interpretation of the event is σ→ nγ(π →Μ Ν), where the π →Μ Ν decay produces no deflection ( θ<0.1 rad) and no significant change in curvature. Using the p-wave radiative decay predictions of Barshay et al. we calculate that the integrated branching ratio for such 'accidental' events is γ(σ →nγ(π →Μ Ν))/γ(σ →nπ)=1.6×10. Most of the contribution to this 'accidental' branching ratio comes from radiative decays where the π mesons have ranges less than 1 mm ( p<20 MeV/ c). If one excludes those Μ's with ranges less than 1.2 cm the above 'accidental' branching ratio becomes 5.5×10. With this figure we estimate that we should have seen 6.5×10 events of this type thusfar in our experiment. The neutron momentum does not help in deciding between the two hypotheses. We therefore assign a confidence level of 7% for the radiative hypothesis. For the leptonic hypothesis we obtain an estimate of the branching ratio, γ(σ →nΜ Ν)/γ(σ →nπ)=5×10. If one further accepts the σ →nπ Ν event reported by Barbaro-Galtieri et al. and the σ →ne Ν event reported by Nauenberg et al., one obtains the δS=−δQ leptonic branching ratio [ γ(σ →nΜ Ν)+γ(σ →ne Ν)]/γ(σ →nπ)=(4±3)×10. [ABSTRACT FROM AUTHOR]

The radiative Σ → nπ γ decay mode was analysed in the 81 cm SACLAY hydrogen bubble chamber exposed to a stopping K beam at the CERN PS. The pion spectrum was measured up to momenta of 150 MeV/c in the Σ rest frame. We obtain the following branching ratios based on 180 Σ→nπγ and 292 Σ→ nπγ events: Γ(Σ → nπ γ)/Γ(Σ→nπ)=(0.93±0.10)×10 Γ(Σ→nπ γ)/Γ(Σ→nπ)=(0.46±0.06)×10. An unambiguous assignment of S-wave to the Σ→nπ and P-wave to Σ→nπ was obtained. The absolute and differential decay rates as well as the parity assignments are in good agreement with theoretical predictions. [ABSTRACT FROM AUTHOR]

A sample of 1.2× 10 Λ-hyperons was analyzed in order to detect the rare decay mode: Λ → pμ¯ v. The Λ-hyperons were produced by stopping K-mesons in the 81 cm Saclay hydrogen bubble chamber at the CERN PS. We obtained for the branching ratio: based on 20 events, of which 6 have to be attributed to the background from the reaction The background was determined by a Monte Carlo calculation. [ABSTRACT FROM AUTHOR]

In a stopping K exposure of the Saclay 81 cm hydrogen bubble chamber, we have obtained a sample of 352 kinematically determined Λ→ pe¯ v dacays. From the electron-neutrino angular distribution of these events, we find the ratio of the axial vector to vector coupling constants ¦ g/ f¦=0.74. This result is in good agreement with Cabibbo's theory. The method of analysis is insensitive to the relative strength of weak magnetism. [ABSTRACT FROM AUTHOR]

All experimental data on leptonic decays of Baryons available after the Kiev Conference on High Energy Physics (Sept. 1970) are used to fit the parameters of the Cabibbo theory. Especially new results on σ and Λ leptonic decays and the values of the Σ lifetime are included. The data are consistent with the one angle Cabibbo theory. The results for the three parameters are: [ABSTRACT FROM AUTHOR]

From about 2 × 10 measured ∑ decay's produced by stopping K mesons in the 81 cm Saclay hydrogen bubble chamber about 140,000 ∑ → n π and 20,000 ∑ → nπ decays were selected for a lifetime measurement. We obtained: [ABSTRACT FROM AUTHOR]

In a bubble chamber experiment about 2×10 Σ-decays have been measured to separate Σ→ne¯ ν events from the two-body modes. No Σ →ne ν event was found whereas 607 Σ→ne¯ ν decays could be identified. The data yield for the Δ Q=−Δ S decay an upper limit: and the branching ratio: [ABSTRACT FROM AUTHOR]