A detection system using drift chambers for the SPES4 spectrometer at Laboratoire National Saturne

We describe the 'drift chamber' detection setup of SPES4, the 4 GeV/c spectrometer at Laboratoire National Saturne. The particle identification is performed by combining magnetic rigidity selection with energy loss and time of flight measurements. This allows to separate analysed isotopes from Z = 1 to at least Z = 10 up to a rigidity of 4 GeV/c. A charge resolution of ΔZrms = 0.1 and a time resolution of Δtrms = 120 ps for 18Ne at about 3 GeV/c per Z are easily obtained. Two sets of multiwire drift chambers are used to measure and reconstruct the particle trajectories at the output of the system. A position resolution better than Δxrms = 160 μm can be achieved in the focal plane. This corresponds to a momentum resolution of Δδrms = 0.22 x 10-4. The performances of SPES4 (Δδrms = 2.2 x 10-4) can then be wholly exploited. (orig.)