J. Heintze

Further measurements on the decay π+ → e+ + ν + γ

The radiative electronic decay pi /sup +/ yields e/sup +/ + nu + gamma is studied because it yields information on nonlocal effects in the decay due to strongly interacting particles or to an intermediate boson transmitting the weak interaction. A 70-Mev pi -meson beam was slowed down by a carbon absorber and e -- gamma coincidences were found. The mass of the intermediate boson is assumed to be (1400 plus or minus 300) Mev/c/sup 2/. (R.E.U.)

A new measurement of the (K+ → e+v)(K+ → μ +v) branching ratio

The branching ratio R = Γ(K+ → e+v)Γ(K+ → μ+v) has been measured on the basis of 534 observed K+ → e+v decays. The K+ decay at rest; the momenta of the e+ and μ+ are measured in a magnetic spectrometer using multiwire driftchambers, and the electrons are identified in a gas Cerenkov counter. The result is R = (2.37 ± 0.17_× 10−5. The value predicted for pure axial-vector interaction and μ-e-universality is R = 2.57 × 10−5.

An experimental investigation of the radiative structure decay K+ → e+υγ☆

The decay K+ → e+υγ has been investigated. For the structure-dependent part with positive γ-helicity (SD+) the branching ratio Γ(SD+)Γ(Kμ2) = (2.33 ± 0.42) × 10−5 is obtained from 51 ± 3 events observed in the kinematical region Ee ⩾ 235 MeV, Eγ > 48 MeV and θeγ > 140°. For the corresponding part with negative γ-helicity we obtain an upper limit Γ(SD−)/Γ(SD+) < 11 (90% CL) from the sample of electrons with energies 220 MeV ⩽ Ee < 230 MeV and with no γ in the backward direction. This upper limit implies that the ratio of structure-dependent axial vector amplitudes lies outside the region −1.8 < aKυK < −0.54. For the decay K+ → e+ννν the limit Γ(K+ → e+ννν)/Γ(Ke2) < 3.8 90% confidence level) was found.

Beta-decay of polarized Λ hyperons I. Measurement of the decay rate☆☆☆

Abstract The branching ratio R = Γ ( Λ → pe ν )/ Γ ( Λ → N π ) has been measured in a counter-spark chamber experiment in which 1078 ± 11 beta-decays of polarized Λ hyperons were observed. The value R = (8.4 ± 0.4) × 10 −4 is obtained.

Further measurements of the π+ → πo + e+ + v decay rate

Calculations based on 38 plus or minus 2 additional events give a value for the branching ratio R = pi /sup +/ yields pi /sup 0/ + e/sup +/ mu /sup +/ + nu of the process pi /sup +/ yields pi /sup 0/ + e/sup +/ + nu of R/ sub exp/ = (1.08 plus or minus 0.21) x R/sub cvc/, where R/sub cvc/ is the value predicted by the conserved vector current theory. Good agreement between experimental and theoretical coupling constants and weak anomalous magnetic moments supports the validity of the conserved vector current theory. (D.C.W.)

A measurement of Kevγ+ decay

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, |νK + aK|2, corresponding to the emission of right handed γ. We find Δ+(SD)/Δ(Ke2) = 1.05−0.30+0.25 and Δ_(SD) < 85 (90% CL). Δ+ is in agreement with theoretical predictions.

A spark chamber experiment on the beta decay of Ξ− hyperons

Abstract A counter-spark chamber experiment to measure the β-decay rate of Ξ− hyperons is described. The Ξ− hyperons were produced by K− of 1.65 GeV/c in a polyethylene target, and their decay observed in an optical spark chamber. A focusing gas Cerenkov counter with cellular structure discriminated between πs and electrons from Ξ− decay. On the basis of 17 ± 1.90.7 observed β-decay events and 374 observed decays representing 1% of the Ξ− decaying through this channel within the spark chamber during the run, a branching ratio R Γ(Ξ − → e νΛ 0 + e νΣ 0 ) Γ(Ξ→πΛ) =(6.8±2.2)×10 −4 , is obtained. From a Cabibbo fit to the other baryon leptonic decays, the branching ratio RCab = 6.0 × 10−4 is expected. As a test of the experimental method, the rate of Λ → evp decay of Λs originating from Ξ− → πΛ decay is evaluated and found to be in agreement with published values.

Beta-decay of polarized Λ hyperons II. Determination of the vector and axial vector form factors☆☆☆

Abstract In the analysis of 1078 ± 11 beta decays of polarized Λ hyperons, the asymmetry parameters α e , α p , and α eν were determined. From these data and the transition rate Γ(Λ → peν the following values for the form factors were obtained: g 1 / f 1 = 0.62 −0.08 +0.09 , f 2 / f 1 = 0.89 ± 0.61 and ¦f 1 ¦= 0.32 ± 0.02; g 2 = 0 is assumed. The results agree with the Cabibbo theory.

Measurement of the e+ polarisation in muon decay by means of bhabha scattering

A method that permits an absolute measurement of the polarization of positrons from meson ( mu /sup +/) decay without slowing down the positrons is described. The method uses positron-electron (Bhabha) scattering in magnetized iron. The magnetized iron provides a target of polarized electrons, and the positron polarization can be evaluated from the scattering asymmetry. (C.E.S.)

A measurement of the π+ → πo + e+ + ν decay rate

The rate of the decay π+ → πo + e+ + ν (ref. [1]), the beta decay of the π+, has been measured by means of a counter scheme, in which this process is detected with an efficiency of 22.4 ± 0.8%. For 1.48 × 1011 π+ coming to rest in the apparatus, 332 ± 10 pion beta decays have been observed. This leads to a branching ratio Rπ+→πo + e+ + νπ+→μ++ν=(1.000.08−0.10)×10−8 corresponding to a decay rate λπ+πo = (0.38 −0.04+0.03) sec−1 in good agreement with the prediction of the CVC theory, λπ+πo (CVC) = (0.393 ± 0.002) sec−1.