Vertical Drift Chambers




The focal plane coordinates are determined in each spectrometer by a package of vertical drift chambers (VDC).

Each package consists of 4 planes, two perpendicular to the dispersive plane, called x-planes, to determine the momentum and the out-of-plane angle of the reconstructed particle. For the other coordinates 2 planes, called s-planes, are tilted by a few degrees.

With this detector we achieve a resolution of

  • dx < 100 µm for the dispersive coordinate
  • dy < 200 µm for the nondispersive coordinate
  • dtheta < 0.3 mrad for the dispersive angle
  • dphi < 1 mrad for the nondispersive angle

The single plane efficiency is better than 99%, leading to an overall efficiency of better than 99.9%.