The NA48/2 experiment at CERN collected a large sample of charged kaon decays to final states with multiple charged particles in 2003–2004. A new upper limit on the rate of the lepton number ...violating decay K±→π∓μ±μ± is reported: B(K±→π∓μ±μ±)<8.6×10−11 at 90% CL. Searches for two-body resonances X in K±→πμμ decays (such as heavy neutral leptons N4 and inflatons χ) are also presented. In the absence of signals, upper limits are set on the products of branching fractions B(K±→μ±N4)B(N4→πμ) and B(K±→π±X)B(X→μ+μ−) for ranges of assumed resonance masses and lifetimes. The limits are in the (10−11,10−9) range for resonance lifetimes below 100 ps.
A precision measurement of the ratio RK of the rates of kaon leptonic decays K±→e±ν and K±→μ±ν with the full data sample collected by the NA62 experiment at CERN in 2007–2008 is reported. The result, ...obtained by analysing ∼150000 reconstructed K±→e±ν candidates with 11% background contamination, is RK=(2.488±0.010)×10−5, in agreement with the Standard Model expectation.
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.
A
bstract
The NA48/2 experiment at CERN reports the first observation of the
K
±
→
π
0
π
0
μ
±
ν
decay based on a sample of 2437 candidates with 15% background contamination collected in 2003–2004. ...The decay branching ratio in the kinematic region of the squared dilepton mass above 0.03 GeV
2
/
c
4
is measured to be (0.65 ± 0.03) × 10
−
6
. The extrapolation to the full kinematic space, using a specific model, is found to be (3.45 ± 0.16) × 10
−
6
, in agreement with chiral perturbation theory predictions.
A sample of 7253 K±→π±e+e−(γ) decay candidates with 1.0% background contamination has been collected by the NA48/2 experiment at the CERN SPS, which allowed a precise measurement of the decay ...properties. The branching ratio in the full kinematic range was measured to be BR=(3.11±0.12)×10−7, where the uncertainty includes also the model dependence. The shape of the form factor W(z), where z=(Mee/MK)2, was parameterized according to several models, and, in particular, the slope δ of the linear form factor W(z)=W0(1+δz) was determined to be δ=2.32±0.18. A possible CP violating asymmetry of K+ and K− decay widths was investigated, and a conservative upper limit of 2.1×10−2 at 90% CL was established.
PDF
