V. Lüth

A new determination of the Ko → π+π− decay parameters

Abstract In a short neutral beam we have measured the proper time-dependence of the decay K o → π + π − . This time structure exhibits the interference between the short- and long-lived states and is in agreement with the general expectations of the CP violation phenomenology. This experiment gives new and more precise measurements of the following three parameters: 1. i) the decay width of the short-lived K S component: Γ S = (1.119±0.006) × 10 10 sec −1 ; 2. ii) the modulus of the CP violating parameter η +- : | η +- | = (2.30±0.035) × 10 −3 ; 3. iii) the phase of η +- as a function of the K S −K L mass difference Δm : φ +- = (49.4±1.0) o + [( Δm −0.540)/0.540] × 305 o The result of |η +- | may be compared with the result of the foregoing letter on Re ϵ in the frame of the superweak model. Good agreement is observed.

CONSTRUCTION AND PERFORMANCE OF LARGE MULTIWIRE PROPORTIONAL CHAMBERS.

Abstract Large-area multiwire proportional chambers have been developed. In particular, a chamber 2 m × 0.5 m, using both horizontal and vertical wires (≈ 1500 wires in all), has been constructed. The chamber performance is very nearly the same as that of smaller chambers. Detailed design and performance data are presented.

A measurement of the KL-KS mass difference from the charge asymmetry in semi-leptonic kaon decays

Abstract The change asymmetry in semi-leptonic kaon decays has been measured as a function of the kaon lifetime. High statistics data of K e3 0 and K μ3 0 decay modes agree with each other and with the general expectation of the CP violation phenomenology together with the ΔS − ΔQ rule. The K L -K S mass difference obtained is Δm = (0.533 ± 0.004) × 10 10 s −1 .

A measurement of the total cross-sections for Λ hyperon interactions on protons and neutrons in the momentum range from 6 GeV/c to 21 GeV/c

Abstract The Λp, Λn, Λ p, and Λ n total cross-sections were measured in the Λ momentum interval 6–21 GeV/ c . Within the experimental uncertainties the cross-sections are momentum-independent in this interval and the momentum-averaged cross-sections are found to be: σ ( Λp ) = 34.6 ± 0.4 mb : σ ( Λn ) = 34.0 ± 0.8 mb ; σ ( Λp ) = 56 ± 11 mb ; σ ( Λn ) = 46 ± 20 mb . The first two results are in agreement with charge symmetry, and with simple quark model sum rules applied to previous results on pp, K - n, and π + p total cross-sections.

Measurement of the kaon mass difference mL-mS by the two regenerator method

Abstract The K0 mass difference has been measured by the two regenerator method. The result is: Δm = mKL − mKS = (0. 534 ± 0.003) × 1010 sec−1.

Measurement of the charge asymmetry in the decays KoL → π±e±ν and KoL → π±μ±ν

The charge asymmetry in semi-leptonic K L 0 decays has been measured in a high statistics experiment using multi-wire proportional chambers. The asymmetry δ = ( N + − N − )/( N + + N − ), where N + and N − are the partial decay rates for K L 0 → π − Q + ν and K L 0 → π + Q − , respectively, is found to be δ L e = (3.41 ± 0.18) × 10 −3 for the K e3 mode, and δ L μ = (3.13 ± 0.29) × 10 −3 for the K μ3 mode. Assuming CPT invariance and the absence of Δ S = −Δ Q transitions, these results lead to a value of the real part of the CP -violation parameter ɛ, Re ɛ = (1.67 ± 0.08) × 10 −3 .

Measurement of the electromagnetic interaction of the neutral kaon

An experiment has been performed to search for the interference between the nuclear and the electron regeneration amplitudes of the neutral kaon. The detailed experimental analysis of the coherent and diffraction nuclear regeneration of long-lived kaons on copper and uranium nuclei has led to a value of the mean square charge radius of the neutral kaon, 〈R2〉 = (0.08 ± 0.05) fm2. The forward regeration amplitudes and the total KL− nucleus cross sections have been determined in auxiliary measurements between 4 and 10 GeV/c.

Measurement of the vector form factor in the decay KL → πev

Abstract The Dalitz plot of 0.5 × 10 6 K e3 decays has been studied to measure the q 2 dependence of the vector form factor, and to determine the effect of radiative corrections. The observed linear slope of the form factor λ + = 0.0312 ± 0.0025 is compatible with the prediction of K ∗ dominance. Deviations of the electron spectra from those of a pure vector transition are measured and found in agreement with expected radiative corrections.

Search for the decay KS → 2μ

Abstract A search for the decay KS → 2μ has given negative results. The 90% confidence upper limit for the branching ratio of 3.1 × 10−7 excludes the models of Christ and Lee, and of Dass and Wolfenstein, designed to explain the KL → 2μ problem.

Search for Delta S=2 Decays of Neutral xi Hyperons

A search for the decay Ξ0→pπ− has been performed in a neutral hyperon beam derived from the 24 GeV/c external proton beam at CERN. The experiment gives as a 90% confidence upper limit for the branching ratio Γ(Ξ0→pπ−)Γ(Ξ0→Λπ0)<3.6×10−5.