Luminosity Enhancements at Slac ’

The hiARK III detector is shown in Figs. l(a) and l(b). The detector is described in Ref. 1 and its main subsystems are described in Refs. 2-6. Briefly, working out from the interaction point, the detector consists of an inner trigger chamber, followed by a large drift chamber, a time-of-flight (TOF) counter system, a gas sampling cylindrical shower counter, a solenoidal coil which generates an axial magnetic field whose value at the interaction point is four kilogauss, the magnet flux-return steel, and finally a muon counter system. Gas sampling endcap shower counters mounted on the removable steel doors complete the detector. The novel feature of the detector is the cylindrical shower counter, which is placed inside the solenoidal coil and has a high detection efficiency for photons with energies as low as 50 MeV.