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