Spherical Neutral Detector tracking system for experiments at VEPP-2000 collider

The new tracking system of the Spherical Neutral Detector for experiments at the VEPP-2000 e+e- collider in Novosibirsk is described. The system consists of a 9-layer drift chamber with 24 jet cells and a proportional chamber in a common gas volume. Main system features are its small size and high density of readout channels for gaseous tracking systems at colliding experiments. The drift chamber provides at least four measurements along the track for charged particles within 94% solid angle and nine measurements for particles propagating at large angle relative to the beam axis. R-ϕ coordinates (in a plane perpendicular to the beam axis) are obtained using the ionization drift time measurement. Longitudial coordinates are measured using charge division on anode wires and charge distribution on cathode strips. Design angular resolutions for radial tracks are σϕ=0.26∘, σθ=0.3∘, the vertex resolution is σR=0.2mm. The full-size prototype of the tracking system has been assembled and tested. The wire structure of the prototype represents one quadrant of the chamber. Results of the prototype assembly quality control and tests with radioactive sources and cosmic rays are presented. They are in a good agreement with expected system parameters.