Development of a compact high density luminosity monitor for ALEPH at LEP-II based on a tungsten-scintillator calorimeter read out by avalanche photodiodes

Experiments with the ALEPH detector at the upgraded e+e− storage ring LEP-II need an extreme forward luminosity monitor to be installed in a very restricted space and in a magnetic fringe field. A high density sandwich electromagnetic calorimeter based on alternating layers of tungsten and plastic scintillators interleaved by one layer of silicon strip counters for precise shower position measurement is under construction. Small avalanche photodiodes, coupled to the scintillator plates by green or yellow wavelength shifting fibers, are being considered as readout element for the calorimeter. The APDs will be followed by low noise, fast preamplifiers. The readout design and first tests will be presented.