Concept and design of the fast H1 second level trigger using artificial neural networks

The experiments at the HERA ep collider have to cope with machine background rates which exceed the rates of the majority of interesting physics interactions by several orders of magnitude. To deal with this the H1 experiment was designed with a four staged trigger system. The second trigger level is currently being equipped with a highly parallel computing system that is specialized to run Artificial Neural Network (ANN) algorithms. The trigger is based on CNAPS neurocomputer boards, which are able to compute multilayer perceptron networks with 64 inputs, 64 hidden nodes and one output node in less than 8 μs. In this contribution we present the concept and design of this system. (author)