H1 LUMI system components and tasks

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=-33.4m

Photon 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=-103.1m

Veto 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=-102.8m

Second Electron Tagger (ET44)
   Fully analogous to ET, but 6 channels only (2 x 3 crystals)
   Position in the tunnel: z=-43.2m

Third Electron Tagger (ET08)
   SpaCal type electromagnetic calorimeter
   Position in the tunnel: z=-8.0m
  
 Lumi 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 DIS
    
 How the system works
   can be illustrated by the graphical example