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
A photograph of the FOCUS Spectrometer and experimental hall. Click on the photograph to view a larger version.