Design of a silicon backward tracking detector and trigger for the H1 experiment at the ep collider HERA

We describe a proposal to upgrade the existing H1 tracking detector by a semiconductor backward tracking telescope consisting of 8 beam concentric discs to measure the gluon and quark distribution functions at very low Bjorken x. Each disc comprises 3 planes of strip and pad Silicon detectors made of 4' wafers in order to determine the polar angle, the transverse momentum and to trigger on deep inelastically scattered electrons. The paper details the simulation work and the layout constraints on the semiconductors and it reviews the technical and electronics design of the trigger which has to cope with very high beam background rates and the HERA bunch crossing rate of 10.4 MHz. A first phase of the project was approved by the H1 collaboration and will be operational in 1994. (orig.)