The ZEUS solenoidal coil of diameter 1.9 m and length 2.6 m
provides a 1.43 T magnetic field for the charged-particle tracking volume.
The tracking system consists of a central wire chamber covering
the polar angular region from 15 to 164
,
a forward planar tracking detector from 8
to 28
and a second planar tracking chamber in the backward direction, covering
the region from 158
to 170
.
The momentum resolution attained is
and
a track is extrapolated to the calorimeter face with a
transverse resolution of about 3 mm.
Ionization measurements from the central tracking chamber
also serve to identify electron-positron pairs from
decays.
The muon system
is constructed of limited streamer tubes inside and outside
of the magnetic return yoke, covering the region in polar angle from
10
to 171
. Hits in the inner chambers
provide muon triggers for
decays.
The ZEUS trigger system consists of three layers.
The first level trigger accepts events at a rate of about 300 Hz.
The read out data are stored in digital or analog pipelines
with a depth of 4.4s
until a global first level trigger decision is received.
At the second level commercially available microprocessors
analyze the digitized data of the components.
The second level trigger processor functions as an asynchronous pipeline,
i.e. a series of parallel processors.
Beam gas background is rejected on the basis of calorimeter timing information
which is available at this stage.
The second level trigger is able to perform
iterative calculations on large fractions of the full event information
which are not possible in the pipelined structure of the first level trigger.
These features enable the second level trigger to achieve a reduction
of the first level trigger rate from
300 Hz to
100 Hz.
The third level trigger provides
a software filter in which the event rate is further reduced to the
level of 15 Hz.