Abstract 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 GeV2/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.
Observation of the rare decay KS→π0e+e Batley, J.R; Kalmus, G.E; Lazzeroni, C ...
Physics letters. B,
12/2003, Letnik:
576, Številka:
1-2
Journal Article
Recenzirano
Odprti dostop
A search for the decay KS→π0e+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→π0e+e−,mee>0.165 GeV/c2)=(3.0+1.5−1.2(stat)±0.2(syst))×10−9 has been measured. Using a vector matrix element and a form factor equal to one, the measurement gives BR(KS→π0e+e−)=(5.8+2.9−2.4)×10−9.
The tagging detector of the CP-violation experiment NA48 at CERN Bergauer, H.; Blümer, H.; Calvetti, M. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
12/1998, Letnik:
419, Številka:
2-3
Journal Article
Recenzirano
Odprti dostop
The CP-violation experiment NA48 at CERN aims at measuring direct CP-violation in the decays of neutral kaons into π+π− and π0π0. The experiment uses simultaneous, almost collinear beams of neutral ...KL0 and KS0 mesons, which are produced on two different targets. KS0 events are “tagged” by measuring the times of the protons that fly towards the KS0 production target. In order to sustain the high rate of 107protons/s in this beam without suffering from too many pile-up events, the detector consists of 24 separate scintillators (12 horizontal and 12 vertical), each of which sees only a small fraction of the beam. Their signals are digitized by specially developed 1GHz FADCs. The exact time of a pulse is established offline by a fit procedure. The detector and its electronics have been successfully used during test beams in 1994–1996 and during the first physics run of NA48 in 1997. The inefficiency of the detector has been measured to 2×10−4. Sources of background have been identified to allow for off-line correction. The mechanical setup of the detector, the 1GHz FADC and results from the test and data runs are presented.
NA48/2 results contributing to ChPT testing are presented. A sample of 1663 events of the rare decay $ K^ \pm \to \mu ^ \pm ve^ + e^ - $ has been selected with a minimum
e
+
e
−
effective mass of 140 ...MeV. The measured model independent decay rate is in agreement with ChPT predictions. The branching ratio of the $ K^ \pm \to \mu ^ \pm ve^ + e^ - $ decay, never observed so far, has been obtained from a sample of about 5000 candidates with less than 6% background, also in agreement with ChPT predictions. In addition, a most precise measurement of the charged kaon semileptonic formfactors has been obtained from 4.4 million
K
e3
and 2.3 million
K
µ3
events collected in 2004.
From the 2002 data taking with a neutral kaon beam extracted from the CERN-SPS, the NA48/1 experiment observed 97 Ξ0→Σ+μ−ν¯μ candidates with a background contamination of 30.8±4.2 events. From this ...sample, the BR(Ξ0→Σ+μ−ν¯μ) is measured to be (2.17±0.32stat±0.17syst)×10−6.
The K sub(S--pisuper+pisuper-esuper+esuper- decay mode was investigated using the data collected in 2002 by the NA48/1 Collaboration. With about 23 k K) sub(S)--pisuper+pisuper-esuper+esuper- events ...and 59 k inline imageinline image normalization decays, the K sub(S--pisuper+pisuper-esuper+esuper- branching ratio relative to the inline imageinline image one was determined to be inline imageinline image. This result was used to set the upper limit)
The decay asymmetries of the weak radiative hyperon decays
Ξ
0
→
Λ
γ
and
Ξ
0
→
Σ
0
γ
have been measured with high precision using data of the NA48/1 experiment at CERN. From about 52 000
Ξ
0
→
Λ
γ
...and 15 000
Ξ
0
→
Σ
0
γ
decays, we obtain for the decay asymmetries
α
Ξ
0
→
Λ
γ
=
−
0.704
±
0.019
stat
±
0.064
syst
and
α
Ξ
0
→
Σ
0
γ
=
−
0.729
±
0.030
stat
±
0.076
syst
, respectively. These results are in good agreement with previous experiments, but more precise.
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