Performance of the new Small Angle Monitor for BAckground (SAMBA) in the ALEPH experiment at CERN

The SAMBA background monitor described here has been installed in the ALEPH experiment at LEP in 1996, replacing the first SAMBA which was in use from 1992 to 1995. Its task is to provide detailed information on the different kinds of beam-induced backgrounds. The main sources of beam related background are synchrotron radiation photons, off-momentum particles, beam-gas interactions and interactions of electrons and positrons with thermal photons in the beam pipe. The SAMBA detector is used to indicate acceptable background conditions for the more sensitive detectors like the time projection chamber (TPC) or the inner tracking chamber (ITC). By measuring arrival times of synchrotron radiation photons, the sources from which these photons have been backscattered can be identified.