The CPLEAR detector at CERN Adler, R.; Albrecht, W.; Alhalel, T. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
09/1996, Letnik:
379, Številka:
1
Journal Article
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The CPLEAR collaboration has constructed a detector at CERN for an extensive programme of CP-, T- and CPT-symmetry studies using K
0 and
K
0 produced by the annihilation of
p
's in a hydrogen gas ...target. The K
0 and
K
0 are identified by their companion products of the annihilation K
±
π
∓ which are tracked with multiwire proportional chambers, drift chambers and streamer tubes. Particle identification is carried out with a liquid Cherenkov detector for fast separation of pions and kaons and with scintillators which allow the measurement of time of flight and energy loss. Photons are measured with a lead/gas sampling electromagnetic calorimeter. The required antiproton annihilation modes are selected by fast online processors using the tracking chamber and particle identification information. All the detectors are mounted in a 0.44 T uniform field of an axial solenoid of diameter 2 m and length 3.6 m to form a magnetic spectrometer capable of full on-line reconstruction and selection of events. The design, operating parameters and performance of the subdetectors are described.
We present a new measurement of the K
L-K
S mass difference (
Δm) using semileptonic decays of neutral kaons. The measurement yields
Δm = (0.5274 ± 0.0029
stat. ± 0.0005
syst.) × 10
10ħ/s.
The time-dependent rate asymmetry of initial K
0 and
K
0 decaying into
π
+
π
−
π
0 was measured in order to reveal the CP-violating amplitude of the K
S →
π
+
π
−
π
0 decay. For the real and the ...imaginary parts of
η
+−0, we find Re(η
+−0) = (6 ± 13
stat. ± 1
syst.) × 10
−3 and Im(η
+−0) = (−2 ± 18
stat. ± 3
syst.) × 10
−3 which correspond to |
η
+−0| < 0.037 with CL.
The interference between CP-conserving Ks and K
L →
π
+
π
−
π
0 decay amplitudes was observed by studying the decay rate asymmetries between initial K
0 and
K
0 separately for the phase space regions
...E
CM(
π
+) >
E
CM(
π
−) and
E
CM(
π
+) <
E
CM(
π
−). For the parameter λ we found Re(λ) = 0.036 ± 0.010(stat.)
−0.003
+0.002(syst.) and Im(λ) consistent with zero, leading to a branching ratio B = 4.1
−1.9
+2.5(stat.)
−0.6
+0.5(syst.) × 10
−7 for the CP-conserving K
S →
π
+
π
−
π
0 decay.
The CP violation parameter
η
+− is determined through the eigentime-dependent asymmetry in the rates of initially tagged K
0 and
K
0 decaying to
π
+
π
−. The obtained values are |
η
+−| = (2.312 ± ...0.043
stat. ± 0.030
syst. ± 0.011
τs) × 10
−3 and
Φ
+− = 42.7° ± 0.9
stat.° ± 0.6
syst.° ± 0.9
Δm
° with
Δ = (527.4 ± 2.9) × 10
7
h
̵
gs
−1
measured in the same experiment using the semileptonic decay channel.
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