DELPHI Forward scintillator HOdoscope (HOF)

Technical description

HOF consists of two identical parts: HOFa and HOFc ( in forward and backward endcaps ). Each of them has 4 quadrants with 28 scintillator counters per quadrant (2x4x28 = 224 counters in total) of 1.5 up to 4.0 m long. On technical reasons the counter has rather small thickness (10 mm) and can be equipped by only one PM tube (on the distant end from the beam line) . As a consequence it is rather high noise rate what we pay to detect efficiently a single MIP signal. This rate is about 400. Hz for each side for 4x4 + 4x4 bunch train mode.

HOF is designated to produce fast and practically standalone trigger on muon event in endcap regions (and single halo muon). The first level HOF's Forward and Backward triggers (MUFW,MUBW) are used by corresponding Muon Chambers. The main HOF trigger is so-called Back-to-Back Second Level trigger. Its efficiency is about 80% and rate is 0.1-0.4 Hz depending on the bunch train mode.

The detector also gives the information on the hit space position and timing which is used for some other detectors calibration. Due to its fast response (less than 50 ns) HOF is able to determine in what bunch in a train did the event happen.