Spectrometer
The FOCUS detector
(schematic)
is a large aperture fixed target multiparticle
spectrometer which features excellent particle identification and vertexing
for charged hadrons and leptons.
A photon beam is
derived from the bremmstrahlung of secondary electrons (E_max = 250 GeV)
produced from the Tevatron proton
beam. This beam impinges on a
beryllium target;
charged particles which emerge from the
target are tracked by two systems of silicon microvertex detectors.
The first system is comingled with the experimental target, the second
is just downstream of the target and consists of twelve
planes of microstrips arranged in three views. These detectors provide
high resolution
separation of primary (production) and secondary (decay) vertices.
The momentum of charged particles is determined by measuring their
deflections in two analysis magnets of opposite polarity
with five stations of multiwire proportional chambers. Straw tubes are
used to supplement tracking in the central pair region.
Three
threshold multicell Cerenkov counters are used to identify electrons, pions,
kaons and protons. There are two electromagetic calorimeters. The inner
calorimeter, a
lead glass block array, covers the central solid angle and detects particles
which pass through the aperatures of both magnets. The outer calorimeter
covers the outer angular anulus described by particles that pass through the
first magnet but not the second. Muons are identified in either
a fine grained scinitilator hodoscope with an iron filter (covering the
inner region) or in
an outer system that uses resistive plate
chambers and the iron yoke of the second magnet as a filter. A
hadron calorimeter consisting of iron and scintillating
tile is used primarily in the experiment trigger but is also used to
reconstruct neutral hadrons.
(1) Original FOCUS Logo
(2) 3-D (Topher) FOCUS Logo
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A photograph of the FOCUS Spectrometer and experimental hall. Click on the photograph to view a larger version. |