The STAR beam-beam counters were scintillator annuli mounted on the outside of the east and west poletips of the STAR magnet. From outside of the STAR magnet looking towards the interaction point along the beam, there are two annuli tiled by small and large hexagonal cells. The large cells have exactly four times the dimensions of the small cells. The small hexagon marked `B' is reserved for the beam pipe. The 1 cm annular clearance between the beam pipe and the inner ring of small hexagonal scintillators sets the scale. A circle of diameter 9.64 cm can be inscribed in the small regular hexagons.
The BBC implementation for the FY2002 RHIC polarized proton run had tiles 1-18 (complete small hexagonal scintillator annulus), 19, 22, 25-26 and 31-32 (partial large hexagonal scintillator annulus) in place on both the east and west poletips of the STAR magnet. All triggers were derived from two sets of eight photomultiplier tubes (PMT) collecting scintillation light from the 18 small hexagonal tiles.
Last Update: 23 June 2018
Original: 6 April 2002