Electron Tagger (ET)
49 channel's crystal Cherenkov calorimeter Total transverse size = 154 x 154 mm Depth = 20cm (22 radiation lengths, X0) Position in the tunnel: z=-33.4mPhoton Detector (PD)
25 channel's crystal Cherenkov calorimeter Total transverse size = 100 x 100 mm Depth = 20cm (22 radiation lenghts, X0) Position in the tunnel: z=-103.1mVeto Counter (VC)
A water Cherenkov detector, readout by 2 PM thus giving 2 channels: spectrometric channel (nominal HV) and veto channel (increased HV) Length along the beam = 28cm (1X0) Position in the tunnel: z=-102.8mSecond Electron Tagger (ET44)
Fully analogous to ET, but 6 channels only (2 x 3 crystals) Position in the tunnel: z=-43.2mThird Electron Tagger (ET08)
SpaCal type electromagnetic calorimeter Position in the tunnel: z=-8.0mLumi System Tasks
a) measure the luminosity without dead time b) tag photoproduction (Q^2 < 0.01GeV^2) c) measure hard photons from the initial state QED radiation in DISHow the system works
can be illustrated by the graphical example