F. James

Errors on ratios of small numbers of events

The correct expression for the error on the ratio of numbers of events is given. Values are tabulated for small numbers of events. Conventionally the normal approximation is used, yielding too small errors. We re-evaluate the errors on some published experimental ratios in e+ e− physics and in neutrino physics.

Experimental study of Ko → π+ π− πo decays and search for CP violation

The time distribution of 180 uniquely identified π+π−πo decays of the Ko meson between 0.04 and 20 KSo lifetimes has been studied. We find that the ratio η+−o of the KSo→π+π−πo to the KLo →π+π−πo amplitude is consistent with no CP violation. Our results confine η+−o to ∼0 < Reη+−o < −2 with small negative values of Imη+−o. If we set Reη−o = 0, we obtain Imη+−o = 0.37−-.34+0.47. If in addition we use the known value of Γ(KLo → π+π−πo) we obtain Imη = −0.23−0.25+0.31. Without these restrictions, a more accurate determination of η+−o can only be made, with the present statistics, by a combination of Ko and Ko data. Assuming η+−o = 0, we find Γ(KLo → π+π−πo = (2.35 ± 0.20) × 106 s−1.

Experimental study of the selection rule ΔS = ΔQ in Koe3 and Koμ3 decays

We have studied the time distribution of semi-leptonic decays of the neutral K meson produced in a hydrogen bubble chamber in the reaction K+p → Kopπ+ with K+ momenta between 1.2 and 1.7 GeV/c. We have identified 306 πev decays and 74 πμv decays of known lepton charge with proper times between 0.04 and 20 KS lifetimes. The results are compatible with no violation of the ΔS = ΔQ rule. For the ratio x of the ΔS = −ΔQ amplitude to the ΔS = ΔQ amplitude we find the values +0.06+0.13inKe3decays:Re⁡xe=0.05inKμ3decays:Re⁡xμ=0.10−0.07−0.16+0.06+0.16Im⁡xe=0.08Im⁡xμ=−0.03−0.07,−0.18. Assuming ΔS = ΔQ we find the rate Γ(KoL → πev + πμv) = (12.4 ± 0.7) × 106 s−1.

Measurement of the KSO mean life

We have measured theKSO mean life using a sample of 50 000 KO → π+π− decays in a hydrogen bubble chamber. We obtain τ = (0.8958 ± 0.0045) × 10−10 s. This value is significantly higher than the present world average of τ = (0.862 ± 0.006) × 10−10 s.

Experimental investigation of ΔSΔQ rule in leptonic K° decays

Abstract A study of 600 000 stopping antiproton annihilations in the Saclay 81 cm hydrogen bubble chamber has yielded about 12 000 visible K° decays, and after many cuts to eliminate background, 121 leptonic K° decays. Straightforward consideration of the time distribution of these leptonic decays yields the following values for the ΔS = ΔQ violating parameter X: Re (X)=0.09 +0.13 −0.11 , Im (X)=−0.22 +0.29 −0.37 .

Measurement of the KS0 → π+π−γ decay rate

Abstract From a study of 70 000 K° decays in the CERN 2m hydrogen bubble chamber, we have estimated the rate for KS0 → π+π−γ for different cuts in the γ momentum. The results are in good agreement with inner bremsstrahlung on KS0 → π+π−. For γ momentum in the K° c.m. greater than 50 MeV/c, we obtain the branching ratio: Γ(KS → π+π−γ, k>50 MeV/c)/Γ(KS→π+π−)=(2.8. ± 0.6)×10−3. This leads to an estimate for the direct γ emission process: Γ(KS→π+π−γ direct)/Γ(KS → π+π−)=(0.3 ± 0.6) × 10−3.

Measurement of the

We have measured theKSO mean life using a sample of 50 000 KO → π+π− decays in a hydrogen bubble chamber. We obtain τ = (0.8958 ± 0.0045) × 10−10 s. This value is significantly higher than the present world average of τ = (0.862 ± 0.006) × 10−10 s.