THE OPTICAL-PROPERTIES OF THE BIGBITE SPECTROMETER AT NIKHEF

The optical properties of the BigBite spectrometer currently in use at the Internal Target Facility of the AmPS ring at NIKHEF have been det ermined. The spectrometer, which consists of a single dipole magnet, c ombines a large solid angle with a large momentum acceptance. The trac k of a particle is determined from the information of two sets of drif t chambers behind the magnet. Tracing this track through the magnetic field to the target yields the position of the scattering vertex and t he size and direction of the momentum vector of the scattered particle at the target position. These quantities are calculated using an anal ytical approximation of the spectrometer, followed by a refinement wit h the matrix method. The sigma-resolutions of the reconstruction for 6 00 MeV electrons are 3 mrad for the angles, 3.2 mm for the vertex posi tion, and 8.4 x 10(-3) for delta p/p. (C) 1998 Elsevier Science B.V. A ll rights reserved.