A sample of more than one million Ke4 decay candidates with less than one percent background contamination has been collected by the NA48/2 experiment at the CERN SPS in 2003-2004, allowing a detailed study of the decay properties. The branching ratio, inclusive of radiative Ke4gamma decays, is measured to be BR(Ke4) = (4.257 +/- 0.016_exp +/- 0.031_ext) x 10-5 with a total relative error of 0.8%. This measurement complements the study of S- and P-wave hadronic form factors by assigning absolute values to the relative hadronic form factors obtained earlier in a simultaneous analysis of the pion-pion scattering lengths conducted on the same data sample. The overall form factor normalization f_s = 5.705 +/- 0.017_exp +/- 0.031_ext is obtained with a total relative precision of 0.6%.

We present a measurement of the ratio of the decay rates Gamma(KL -> pi+ pi-)/Gamma(KL -> pi e nu), denoted as Gamma(K2pi)/Gamma(Ke3). The analysis is based on data taken during a dedicated run in 1999 by the NA48 experiment at the CERN SPS. Using a sample of 47000 K2pi and five million Ke3 decays, we find Gamma(K2pi)/Gamma(Ke3) = (4.835 +- 0.022(stat) +- 0.016(syst)) x 10^-3. From this we derive the branching ratio of the CP violating decay KL -> pi+ pi- and the CP violation parameter |eta+-|. Excluding the CP conserving direct photon emission component KL -> pi+ pi- gamma, we obtain the results BR(KL -> pi+ pi-) = (1.941 +- 0.019) x 10^-3 and |eta+-| = (2.223 +- 0.012) x 10^-3.

The beam and detector, used for the NA48 experiment, devoted to the measurement of Re(ε′/ε), and for the NA48/1 experiment on rare KS and neutral hyperon decays, are described.

This paper reports on a new high precision measurement of the form factors of the KL → π μ νμ decay. The data sample of about 2.3×106 events was recorded in 1999 by the NA48 experiment at CERN. Studying the Dalitz plot density we measured a linear, λ ′ + = (20.5±2.2stat±2.4syst)×10, and a quadratic, λ ′′ + = (2.6± 0.9stat ± 1.0syst) × 10 term in the power expansion of the vector form factor. No evidence was found for a second order term for the scalar form factor; the linear slope was determined to be λ0 = (9.5±1.1stat±0.8syst)×10. Using a linear fit our results were: λ+ = (26.7±0.6stat ±0.8syst)×10 and, λ0 = (11.7±0.7stat ±1.0syst)×10. A pole fit of the form factors yields: mV = (905 ± 9stat ± 17syst) MeV/c and mS = (1400 ± 46stat ± 53syst) MeV/c.

This Letter reports on a new high precision measurement of the form factors of the K-L -> pi(+/-) mu(-/+) nu(mu) decay. The data sample of about 2.3 x 10(6) events was recorded in 1999 by the NA48 experiment at CERN. Studying the Dalitz plot density we measured a linear, lambda(+)' = (20.5 +/- 2.2(stat) +/- 2.4(syst)) x 10(-3), and a quadratic, lambda(+)''(2.6 +/- 0.9(stat) +/- 1.0(syst)) x 10(-3) term in the power expansion of the vector form factor. No evidence was found for a second order term for the scalar form factor; the linear slope was determined to be lambda(o) = (9.5 +/- 1.1(stat) +/- 0.8(syst)) x 10(-3). Using a linear fit our results were: lambda(+) = (26.7 +/- 0.6(stat) +/- 0.8(syst)) x 10(-3) and lambda(o) = (11.7 +/- 0.7(stat) +/- 1.0(syst)) x 10(-3). A pole fit of the form factors yields: M-V = (905 +/- 9(stat) +/- 17(syst)) MeV/c(2) and m(S) = (1400 +/- 46(stat) +/- 53(syst)) Mev/c(2). (c) 2007 Elsevier B.V. All rights reserved.

The decay rate of the long-lived neutral K meson into the e+e−e+e− final state has been measured with the NA48 detector at the CERN SPS. Using data collected in 1998 and 1999, a total of 200 events has been observed with negligible background. This observation corresponds to a branching ratio of Br(KL→e+e−e+e−)=(3.30±0.24stat±0.23syst±0.10norm)×10−8.

Using data taken during the year 2000 with the NA48 detector at the CERN SPS, a search for the CP violating decay K_S ->3 pi0 has been performed. From a fit to the lifetime distribution of about 4.9 million reconstructed K0/K0bar ->3 pi0 decays, the CP violating amplitude eta_000 = A(K_S ->3 pi0)/A(K_L ->3 pi0) has been found to be Re(eta_000) = -0.002 +- 0.011 +- 0.015 and Im(eta_000) = -0.003 +- 0.013 +- 0.017. This corresponds to an upper limit on the branching fraction of Br(K_S ->3 pi0)<7.4 x 10^-7 at 90% confidence level. The result is used to improve knowledge of Re(epsilon) and the CPT violating quantity Im(delta) via the Bell-Steinberger relation.

We present a measurement of the relative branching ratio of the decay K-0 --> pi(+/-)e(+/-)nugamma (K-e3gamma) with respect to K-0 --> pi(+/-)e(+/-)nu (K-e3 + K-e3gamma) decay. The result is based on observation of 19000 K-e3gamma and 5.6 x 10(6) K-e3 decays. The value of the branching ratio is Br(K-e3gamma(,)0 E-gamma(*) > 30 MeV, theta(egamma)(*) > 20degrees)/Br(K-e3(0)) = (0.964 +/- 0.008(-0.009)(+0.011))%. This result agrees with theoretical predictions but is at variance with a recently published result. (C) 2004 Elsevier B.V. All rights reserved.

For liquid argon calorimeters electronegative impurities dissolved in the medium degrade the detector response and deteriorate the energy resolution, especially at high energies. A concept for a purity monitoring system for liquid argon calorimeters has been developed and is presented here. Special combined monitors of 241Am- and 207Bi-cells are used to monitor the concentration of impurities. The working principle as well as results from test measurements are discussed.

In data taken with the NA48 experiment at the CERN SPS in 1999, 730 candidates of the weak radiative hyperon decay Ξ0→Λγ have been found with an estimated background of 58±8 events. From these events the Ξ0→Λγ decay asymmetry has been determined to α(Ξ0→Λγ)=−0.78±0.18stat±0.06syst, which is the first evidence of a decay asymmetry in Ξ0→Λγ. The branching fraction of the decay has been measured to be Br(Ξ0→Λγ)=(1.16±0.05stat±0.06syst)×10−3.

In data taken with the NA48 experiment at the CERN SPS in 1999, 730 candidates of the weak radiative hyperon decay Xi(0) --> Lambdagamma have been found with an estimated background of 58 +/- 8 events. From these events the Xi(0) --> Lambdagamma decay asymmetry has been determined to alpha(Xi(0) --> Lambdagamma) = -0.78 +/- 0.18(stat) +/- 0.06(syst), which is the first evidence of a decay asymmetry in Xi(0) --> Lambdagamma. The branching fraction of the decay has been measured to be Br(Xi(0) --> Lambdagamma) = (1.16 +/- 0.05(stat) +/- 0.06(syst)) x 10(-3). (C) 2004 Elsevier B.V. All rights reserved.

Using the NA48 detector at the CERN SPS, 31 KS->pi0 gamma gamma candidates with an estimated background of 13.7 +- 3.2 events have been observed. This first observation leads to a branching ratio of BR(KS->pi0 gamma gamma) = (4.9 +- 1.6(stat) +- 0.9(syst)) x 10^-8 in agreement with Chiral Perturbation theory predictions.

This Letter reports on a new high precision measurement of the form factors of the KL→π±μ∓νμ decay. The data sample of about 2.3×106 events was recorded in 1999 by the NA48 experiment at CERN. Studying the Dalitz plot density we measured a linear, λ+′=(20.5±2.2stat±2.4syst)×10−3, and a quadratic, λ+″=(2.6±0.9stat±1.0syst)×10−3 term in the power expansion of the vector form factor. No evidence was found for a second order term for the scalar form factor; the linear slope was determined to be λ0=(9.5±1.1stat±0.8syst)×10−3. Using a linear fit our results were: λ+=(26.7±0.6stat±0.8syst)×10−3 and λ0=(11.7±0.7stat±1.0syst)×10−3. A pole fit of the form factors yields: mV=(905±9stat±17syst)MeV/c2 and mS=(1400±46stat±53syst)MeV/c2.

We present a new measurement of the branching ratio R of the decay KL -> pi e nu (Ke3), relative to all charged KL decays with two tracks, based on data taken with the NA48 detector at the CERN SPS. We measure R = 0.4978 +- 0.0035. From this we derive the Ke3 branching fraction and the weak coupling parameter |Vus| in the CKM matrix. We obtain |Vus|f+(0) = 0.2146 +- 0.0016, where f+(0) is the vector form factor in the Ke3 decay.

The KL → π+π−e+e− andKS → π+π−e+e− decay modes have been studied in detail using the NA48 detector at the CERN SPS. Based on the data collected during the 1998 and 1999 run periods, a sample of 1162 KL → π+π−e+e− candidates has been observed with an expected background level of 36.9 events, yielding the branching ratio measurement BR(KL → π+π−e+e−)=(3.08 ± 0.20) × 10−7. The distribution of events in thesinφ cosφ variable, whereφ is the angle between the π+π− and thee+e− decay planes in the kaon centre of mass, is found to exhibit a large CP-violating asymmetry with the valueAφ=(14.2 ± 3.6)%. For theKS → π+π−e+e− decay channel, 621 candidates have been identified in the 1999 data sample with an estimated background contribution of0.7 event. The corresponding branching ratio has been determined to be BR(KS → π+π−e+e−) = (4.71 ± 0.32) × 10−5. The combined value of this measurement with the published 1998 result is BR(KS → π+π−e+e−) = (4.69 ± 0.30) × 10−5. No asymmetry is observed in this decay mode. Our results are in good agreement with theoretical predictions based on a phenomenological description of radiative kaon decays. The form factor parameters a1/a2 and g̃M1 in theKL → π+π−e+e− direct emission process as well as the value of the K0 charge radius have been extracted from the data.

The K-S --> gammagamma decay rate has been measured with the NA48 detector using a high intensity short neutral beam from the CERN SPS. The measured branching ratio BR(K-S gammagamma) = (2.78 +/- 0.06(stat) +/- 0.04(syst)) x 10(-6), obtained from 7461 +/- 172 K-S --> gammagamma events, is significantly higher than the O(p(4)) prediction of chiral perturbation theory. Using a K-L beam the ratio Gamma(K-L-->gammagamma)/Gamma(K-L-->pi(0)pi(0)pi(0)) = (2.81 +/- 0.01(stat) +/- 0.02(syst)) x 10(-3) has been measured. (C) 2002 Elsevier Science B.V All rights reserved.