We report the results from a study of the full sample of ∼6.031×107K±→π±π0π0 decays recorded by the NA48/2 experiment at the CERN SPS. As first observed in this experiment, the π0π0 invariant mass ...(M00) distribution shows a cusp-like anomaly in the region around M00=2m+, where m+ is the charged pion mass. This anomaly has been interpreted as an effect due mainly to the final state charge exchange scattering process π+π−→π0π0 in K±→π±π+π− decay. Fits to the M00 distribution using two different theoretical formulations provide the presently most precise determination of a0−a2, the difference between the ππ S-wave scattering lengths in the isospin I=0 and I=2 states. Higher-order ππ rescattering terms, included in the two formulations, allow also an independent, though less precise, determination of a2.
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
K
S
and neutral hyperon decays, are described.
A
bstract
A measurement of the form factors of charged kaon semileptonic decays is presented, based on 4.4 × 10
6
K
±
→
π
0
e
±
ν
e
(
K
e
3
±
) and 2.3 × 10
6
K
±
→
π
0
μ
±
ν
μ
(
K
μ
3
±
) decays ...collected in 2004 by the NA48/2 experiment. The results are obtained with improved precision as compared to earlier measurements. The combination of measurements in the
K
e
3
±
and
K
μ
3
±
modes is also presented.
The KS→γγ 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(KS→γγ)=(2.78±0.06stat±0.04syst)×10−6, ...obtained from 7461±172 KS→γγ events, is significantly higher than the O(p4) prediction of chiral perturbation theory. Using a KL beam the ratio Γ(KL→γγ)Γ(KL→π0π0π0)=(2.81±0.01stat±0.02syst)×10−3 has been measured.
In an earlier paper 1, the background for Ke3 was over estimated due to an erroneous calculation of the electron identification efficiency. The correct ratios of the partial widths involving this ...channel are \(\mathcal{R}_{K e 3 / K2\pi} = 0.2470\pm0.0009\, ({\text{stat}})\pm0.0004\, ({\text{syst}})\) and \(\mathcal{R}_{K \mu3 / Ke3} = 0.663\pm0.003\,({\text{stat}})\pm0.001\,({\text{syst}})\). Assuming the PDG value 2 for the K2π branching ratio, the measured branching fraction of Br (Ke3) continues to exceed the current PDG value 2. The extracted value of |Vus|f+(0) is in agreement with the CKM unitary prediction; thus, our conclusions in 1 do not change.
A measurement of the direct CP violating charge asymmetries of the Dalitz plot linear slopes Ag=(g+-g-)/(g++g-) in K±→π±π+π- and K±→π±π0π0 decays by the NA48/2 experiment at CERN SPS is presented. A ...new technique of asymmetry measurement involving simultaneous K+ and K- beams and a large data sample collected allowed a result of an unprecedented precision. The charge asymmetries were measured to be Acg=(-1.5±2.2)×10-4 with 3.11×109K±→π±π+π- decays, and Ang=(1.8±1.8)×10-4 with 9.13×107K±→π±π0π0 decays. The precision of the results is limited mainly by the size of the data sample.
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