The superconducting toroidal spectrometer for hypernuclear studies at KEK-PS

A spectrometer using a toroidal magnet with 12 superconducting coils was constructed at the north experimental hall of the KEK 12 GeV proton synchrotron. The spectrometer comprised 12 individual sectors surrounding the target point and served to measure π− momentum for the purpose of hypernuclear studies via the (stopped K−, π−) reaction. A large solid angle of more than 6%×4π str was achieved in a wide momentum range between 180 and 350 MeV/c at the maximum 1.8 T magnetic excitation, and in a range between 70 and 150 MeV/c at 0.65 T. A momentum resolution of 1.5 MeV/c FWHM was measured at 205 MeV/c, and a resolution around 3 MeV/c FWHM at 130–200 MeV/c was obtained including energy loss fluctuation in the experimental thick targets.