K. Kleinknecht

Observation of the decay K(L) ---> pi0 gamma gamma

Abstract The decay mode K L → π 0 γγ has been observed with a signal of 21 events and an expected background of 1.5±0.9 events. A branching ratio for decays with invariant γγ masses above 280 MeV of (2.1±0.6)×10 −6 is calculated. This result is compared with the values estimated from theoretical models and has implications for the CP conserving contribution to K L → π 0 e + e − decay.

Interference between KL → π+π- and KS → π+π- behind a copper regenerator

Abstract The interference between K L → π + π - and K S → π + π - behind a copper regenerator has been observed in a high statistics experiment. The modulus and the argument of the complex ratio ϱ ( p )/ η +- , where ϱ ( p ) is the regeneration amplitude and η +- = A ( K L → π + π - )/ A (K S → π + π - ) has been measured over the momentum interval from 2.0 GeV/ c to 6.0 GeV/ c . The phase of η +- as deduced from this measurement and from the optical model value of arg [ ϱ ( p )] is 49.3° ± 6.8°. The K L K S mass difference has been found to be Δm/ h = (0.555 ± 0.020) × 10 10 sec −1 .

On KL - KS regeneration in copper

Abstract The transmission regeneration amplitude after a thick copper block has been measured. The quantity ∣ƒ(0)− ƒ (0)∣ k varies from 20.0 ± 1.4 mb at 2.75 GeV/ c to 13.6 ± 1.2 mb at 7.25 GeV/ c . Results are in agreement with optical model calculations in which real and imaginary parts of the amplitudes for single nucleon scattering are determined from forward dispersion relations and total cross-sections.

A precision determination of the KL - KS mass difference

Abstract The K L - L S mass difference has been measured to be δm = (0.542 ± 0.006) × 10 10 sec −1 . Combined with K L - L S interference experiments in the π + π − decay channel, the experiment gives an improved value for arg (K L → π + π − /K S → π + π − ).

Pomeranchuk theorem and KL-KS regeneration

Abstract A sensitive test of the Pomeranchuk theorem can be performed by measuring the interference effects between KS → π+π− and KL → π+π− behind a regenerator at 20–60 GeV/c. This method gives not only the total cross-section differences between K0 and K 0 on nucleus, but also the difference of the real parts of the K0, K 0 forward scattering amplitudes.

Angular dependence of KLKS regenerative scattering for copper and lead nuclei at high energies

Abstract Elastic and inelastic K L  S regenerative scattering on copper and lead nuclei have been observed up to a momentum transfer of 0.17 GeV/ c . The elastic differential cross-section is of a ”diffractive” type. It can be described successfully in terms of an optical model only assuming an appreciable neutron excess in the vicinity of the nuclear surface.

Observation of time-dependent KS and KL interference in the π+π− decay channel from an initial K0 state

Abstract The phase ϕ +− between the amplitudes K L → π + π − and K S → π + π − has been measured. The result is 46 0 ± ± 15 0 for a K L - K S mass difference Δm/ h = (0.526±0.20) × 10 10 s −1 , in good agreement with the “superweak model” of Wolfenstein which predicts ϕ +− SW = 42.6 0 ± 1.0 0 .

Search for coherent regeneration from electrons the K0 charge radius

Abstract We have searched for coherent interactions of a long-lived neutral kaon with the electrons of lead and copper plates. Results are compatible with the absence of such effects. In terms of the kaon r.m.s. charge radius we find 〈 R 2 〉 = 0.22 − 0.22 + 0.20 fm .

The phase difference between KL → π+π− and KS → π+π− decay amplitudes

The phase difference between the KL → π+π− and KS → π+π− decay amplitudes has been measured by observing the time dependence of the π+π− decay intensity from an initial K° (strangeness = +1) state. The phase difference φ/+− is found to be 41° ± 12° for a KL − KS mass difference Δm/h = 0.526 × 1010sec−. The error includes statistical and systematic uncertainties. The phase φ+− is strongly correlated to the value adopted for Δm/h. The present uncertainty on Δm/h increases our error on φ+− from 12° to 15°. The result is in agreement with the prediction of the ‘superweak model’ of CP violation.

The ΔS = ΔQ rule in the decay Ko → e± + ν + π

Abstract The magnitude of the charge asymmetry in Ke3 decay following a regenerator is analysed with the help of auxiliary experiments which determine the magnitude of the regeneration amplitude. It is found that (1 − |x| 2 ) |1 + x | 2 = (1.06±0.06) , where x is the ΔS − ΔQ violating amplitude relative to the ΔS = ΔQ conserving amplitude. The test is more sensitive than previous tests of ΔS ± ΔQ conservation, and in agreement with no violation.