556
K. Kleinknecht and U. Uwer
the low energy ¯
p ring LEAR at CERN. The antiprotons were stopped in a 16 bar
hydrogen gas target and formed a protonium before annihilation. In annihilation
reactions of the type ¯
pp → K 0 K − π + and ¯
pp → K 0 K + π − , the charged kaon was
identified through the time of flight and track curvature in a solenoidal magnetic
field (“tagging”). This tag was used as a trigger for detecting the decay products
of the neutral K meson associated with the K + or K − . A unique property of this
scheme is that the strangeness of the neutral K meson is known from the charge of
the tagged K + or K − .
As shown in Fig. 9.10, the experiment had a cylindrical, onion-type, setup. Six
cylindrical drift chambers, starting at a radius of 25.46 cm and going out to a radius
of 50.95 cm, provided the main tracking information for charged particles. The
offline track-finding efficiency was better than 99% and the wire positions were
determined with an accuracy of about 10 μm. The mean mass resolution achieved
for the invariant kaon mass in the π + π − final state was 13.6 MeV/c 2 . By applying
kinematically and/or geometrically constrained fits, the K 0 momentum resolution
σ p t /p t was improved from 5.5% to 0.25%.
The tracking detectors were followed by the particle identification detector
(PID), used for charged-kaon identification and e/π separation. It was located at
radii between 62.5 cm and 75.0 cm. and was composed of two layers of plastic
scintillators with an 8 cm thick liquid threshold Cerenkov detector in between.
The two charged tracks from the decays K 0 → π + π − , π + e − ν, π + μ − ν were
reconstructed and the decay vertex was calculated. Using this vertex and the
annihilation point in the hydrogen target, the proper time for decay of the kaon
was obtained.
Magnet coils
Al support rings
Beam monitor
Streamer tubes
Drift chambers
Proportional chambers
16 bar H target
2
1 m
200 MeV/c
p
Cherenkov and Scintillator counters
Electromagnetic calorimeter
Fig. 9.10 CPLEAR detector
K. Kleinknecht and U. Uwer
the low energy ¯
p ring LEAR at CERN. The antiprotons were stopped in a 16 bar
hydrogen gas target and formed a protonium before annihilation. In annihilation
reactions of the type ¯
pp → K 0 K − π + and ¯
pp → K 0 K + π − , the charged kaon was
identified through the time of flight and track curvature in a solenoidal magnetic
field (“tagging”). This tag was used as a trigger for detecting the decay products
of the neutral K meson associated with the K + or K − . A unique property of this
scheme is that the strangeness of the neutral K meson is known from the charge of
the tagged K + or K − .
As shown in Fig. 9.10, the experiment had a cylindrical, onion-type, setup. Six
cylindrical drift chambers, starting at a radius of 25.46 cm and going out to a radius
of 50.95 cm, provided the main tracking information for charged particles. The
offline track-finding efficiency was better than 99% and the wire positions were
determined with an accuracy of about 10 μm. The mean mass resolution achieved
for the invariant kaon mass in the π + π − final state was 13.6 MeV/c 2 . By applying
kinematically and/or geometrically constrained fits, the K 0 momentum resolution
σ p t /p t was improved from 5.5% to 0.25%.
The tracking detectors were followed by the particle identification detector
(PID), used for charged-kaon identification and e/π separation. It was located at
radii between 62.5 cm and 75.0 cm. and was composed of two layers of plastic
scintillators with an 8 cm thick liquid threshold Cerenkov detector in between.
The two charged tracks from the decays K 0 → π + π − , π + e − ν, π + μ − ν were
reconstructed and the decay vertex was calculated. Using this vertex and the
annihilation point in the hydrogen target, the proper time for decay of the kaon
was obtained.
Magnet coils
Al support rings
Beam monitor
Streamer tubes
Drift chambers
Proportional chambers
16 bar H target
2
1 m
200 MeV/c
p
Cherenkov and Scintillator counters
Electromagnetic calorimeter
Fig. 9.10 CPLEAR detector