DM2, A Magnetic Detector for the Orsay Storage Ring DCI

Abstract

DM2 is the magnetic detector built to study e+e- interactions in the c.m. energy range 1.2-3.7 GeV with the Orsay Storage Ring DCI. The magnet is a solenoid of 2 m diameter and 3 m length with a conventional aluminium coil producing a 0.5 T field.Inside the coil, the charged particles detector is made of two proportional chambers with anode and cathode read-outs, 13 layers of drift chambers, one layer of water Cerenkov counters and one layer of scintillation counters.Photon detection is provided outside the 1 rad length coil by stacks of 14 planes of wire tubes with longitudinal read-outs, separated by lead sheets, and by five layers of scintillation counters. Inside the coil, the end caps are covered by shower detectors made of lead sheets and MWPC planes.Muon separation uses the flux return iron or concrete absorbers, and planes of wire tubes with longitudinal read-out.The charged particle detector covers 87% or 4π and the photon detector 82% of 4π. Charged particle identification by time of flight and Cerenkov radiation can discriminate pions from kaons up to 600 MeV/c and kaons from protons up to 1100 MeV/c. The photon detection efficiency is 50% at 50 MeV and near 100% at 100 MeV. It allows a neutral trigger to be operated. The detector is starting operation on the storage ring DCI at Orsay.