L. Bertanza

A measurement of the phases of the CP-violating amplitudes in K0→2π decays and a test of CPT invariance

Abstract The phases of the CP-violating amplitudes in K0→π+π− and K0→2π0 decays, φ+−=46.9°±2.2° and φ00=47.1°±2.8°, have been measured in the same experiment, and a direct comparison gives the phase difference φ00−φ+−=0.2°±2.9°. This result leads to an upper limit on possible CPT violation in the K0 mass matrix, of |(m K 0 −m K 0 )/m K 0 | −18 at the 95% confidence level and is the most stringent test of the equality of particle and antiparticle masses.

Observation of the decay KL→π0γγ

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.

Observation of the decay Ks → 2γ and measurement of the decay rates KL → 2γ and KS → 2γ

Abstract The decay rates of K L → 2γ and K S → 2γ have been measured at the CERN SPS. The results are Γ (K L →2 γ )/ χ (K L →2 π 0 )=0.632±0.004±0.008 and Γ (K S →2 γ )/ Γ (K L →2 γ )=2.3 ±1.0±0.4. This is the first observation of K S →2γ decays.

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.

Search for the decay KL→π0e+e−

A search for the decay KL→π0e+e− has been performed at the CERN SPS. One candidate event has been found, compatible with an expected background of 1.5 events. The corresponding upper limit for the branching ration is Γ(KL→π0e+e−)Γ(KL → all)<4×10−8 with 90% confidence.

Search for a neutral Higgs particle in the decay sequence KL0→π0H0 and H0→e+e−

Abstract We have searched for the sequence of decays K L 0 → π 0 H 0 and H 0 →e + e − at the CERN Super Proton Synchrotron (SPS), and have allowed for a non-zero H 0 lifetime. Three candidates have been seen, consistent with an expected background of 3.3. Limits on the branching ratio product in the range 10 −8 –10 −7 are presented as a function of the mass and lifetime of the H 0 . These can be used to restrict the neutral Higgs of the minimal standard model.

Search for a Neutral Higgs Particle in the Decay Sequence

Abstract We have searched for the sequence of decays K L 0 → π 0 H 0 and H 0 →e + e − at the CERN Super Proton Synchrotron (SPS), and have allowed for a non-zero H 0 lifetime. Three candidates have been seen, consistent with an expected background of 3.3. Limits on the branching ratio product in the range 10 −8 –10 −7 are presented as a function of the mass and lifetime of the H 0 . These can be used to restrict the neutral Higgs of the minimal standard model.