A forward magnetic spectrometer system for high-energy heavy-ion experiments

A small aperture magnetic spectrometer has been built to study hadron production in 197 Au + 197 Au collisions at the AGS energy of 11.6A GeV/c. It operates in the forward angular range from 6 to 30° with respect to the incident beam axis and covers the mid-rapidity region for heavy particles such as protons. The detector components of the spectrometer system include two time projection chambers, four drift chamber modules and a time-of-flight scintillation counter wall. A few new technologies are implemented in the design of the system to achieve the performance goals. The spectrometer has proved to function properly under the high particle-density environment encountered in experiments with the heavy-ion colliding system. The achieved momentum resolution is 1.3% in r.m.s. for pions at 1 GeV/c and 1.6% for protons at the same momentum. With the time-of-flight resolution of 76 ps in r.m.s., the particle identification momentum limit extends to 4 GeV/c for pions, 3 GeV/c for kaons, 5 GeV/c for protons, and 4.5 GeV/c for anti-protons. The tracking efficiency stays above 86% for tracks up to 5 GeV/c with as many as 10 tracks in the spectrometer aperture.