To guarantee the observation of standard model CP violation
in B decays (after folding in the detector efficiencies),
interactions at the HERA-B detector have to occur
approximately 4 times for every one of the 10 MHz bunch crossings of the HERA
machine. The HERA-B experiment is essentially a fixed target experiment
with a wire target in the beam halo [8].
A schematic of the HERA-B
spectrometer is shown in fig. 6.
It has a single dipole momentum spectrometer
situated 4.5 m downstream of the target.
Directly downstream of the target wires, but before the magnet, there is
a silicon vertex detector
of length of The main tracking system uses a variety
of technologies dependent on the distance away from the beam (Si-strips,
microstrip gas counters and honeycomb-drift chambers at ever increasing
radii from the beam.) This is followed by a ring imaging Cerenkov
(RICH) detector to tag the charged kaon and a transition radiation detector to
improve electron identification. There are additional large tracking
chambers immediately behind the RICH and in front of the
calorimeter. The electromagnetic calorimetry is designed to use
Lead/Scintillator and Tungsten/Scintillator. This is followed by a
conventional muon system with four chamber layers at various depths in
the absorber. The muon chambers are essential for the triggering
of HERA-B when the
decays to two muons.
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