The neural network first level trigger for the DIRAC experiment

The neural network first level trigger for the DIRAC experiment at CERN is presented. Both the neural network algorithm used and its actual hardware implementation are described. The system uses the fast plastic scintillator information of the DIRAC spectrometer. In 210 ns it selects events with two particles having low relative momentum; such events are selected with an efficiency of more than 0.94. The corresponding rate reduction for background events is a factor of 2.5.