We report the results from a study of a partial sample of similar to 2.3 x 10(7) K+/- -> pi(+/-)pi(0)pi(0) decays recorded by the NA48/2 experiment at the CERN SPS, showing an anomaly in the pi(0)pi(0) invariant mass (M-00) distribution in the region around M-00 = 2m(+), where m(+) is the charged pion mass. This anomaly, never observed in previous experiments, can be interpreted as an effect due mainly to the final state charge exchange scattering process pi(+)pi(-) -> pi(0)pi(0) in K+/- -> pi(+/-)pi(+)pi(-) decay [N. Cabibbo, Phys. Rev. Lett. 93 (2004) 121801]. It provides a precise determination of a(0) - a(2), the difference between the pi pi scattering lengths in the isospin I = 0 and I = 2 states. A best fit to a rescattering model [N. Cabibbo, G. Isidori, JHEP 0503 (2005) 21] corrected for isospin symmetry breaking gives (a(0) - a(2))m(+) = 0.268 +/- 0.010(stat) +/- 0.004(syst), with additional external uncertainties of +/- 0.013 from branching ratio and theoretical uncertainties. If the correlation between a(0) and a2 predicted by chiral symmetry is taken into account, this result becomes (a(0) - a(2))m(+) = 0.264 +/- 0.006(stat) +/- 0.004(syst) +/- 0.013(ext). (c) 2005 Elsevier B.V. All rights reserved.

We report a measurement of the direct CP violation asymmetry parameter A(g) in charged kaon decays K+/- -> pi(+/-)pi(+)pi(-) by the NA48/2 experiment at the CERN SPS. The experiment has been designed not to be limited by systematics in the asymmetry measurement. Using 1.67 x 10(9) such decays collected during the 2003 run, the charge asymmetry in the Dalitz plot linear slope parameter g has been measured to be A(g) = (1.7 +/- 2.9) x 10(-4). The precision of the result is limited by the statistics used. (c) 2006 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.

The NA48 Collaboration has measured the amplitude of the CP-conserving component of the decay KS0→π+π−π0 relative to KL0→π+π−π0. For the characteristic parameter λ, the values Reλ=0.038±0.010 and Imλ=−0.013±0.007 have been extracted. These values agree with earlier measurements and with theoretical predictions from chiral perturbation theory.

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.

The KL→π±π0e∓νe(ν̄e) decay was investigated with the NA48 detector at CERN SPS using a beam of long-lived neutral kaons. The branching ratio Br(KL→π±π0e∓νe(ν̄e))=(5.21±0.07stat±0.09syst)×10−5 was fixed from a sample of 5464 events with 62 background events. The form factors f̄s, f̄p, λg and h̄ were found to be in agreement with previous measurements but with higher accuracy. The coupling parameter of the chiral Lagrangian L3=(−4.1±0.2)×10−3 was evaluated from the data.

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.

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.

A search for the decay KS→π0μ+μ− has been made by the NA48/1 Collaboration at the CERN SPS accelerator. The data were collected during 2002 with a high-intensity KS beam. Six events were found with a background expectation of 0.22−0.11+0.18 events. Using a vector matrix element and unit form factor, the measured branching ratio is B(KS→π0μ+μ−)=[2.9−1.2+1.5(stat)±0.2(syst)]×10−9.

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.

A search for the decay Ks->pi0e+e- has been made by the NA48/1 experiment at the CERN SPS accelerator. Using data collected during 89 days in 2002 with a high-intensity Ks beam, 7 events were found with a background of 0.15 events. The branching fraction BR(Ks->pi0e+e-, m(ee) > 0.165 GeV/c^2) = (3.0^{+1.5}_{-1.2}(stat) +/-0.2 (syst)) x 10^{-9} has been measured. Using a vector matrix element and a form factor equal to one, the measurement gives BR(Ks->pi0e+e-) = (5.8^{+2.9}_{-2.4}) x 10^{-9}.

A search for the decay K-S --> pi(0)gammagamma has been made using the NA48 detector at the CERN SPS. Using data collected in 1999 during a 40-hour run with a high-intensity K-S beam, an upper limit for the branching ratio BR(K-S --> pi(0)gammagamma, z greater than or equal to 0.2) < 3.3 x 10(-7) has been obtained at 90% confidence level, where z = m(gammagamma)(2)/m(K0)(2). (C) 2003 Published by Elsevier Science B.V.