Study of the vertex trigger performance on test-beam data

99-030 The performance of the Level-1 vertex trigger algorithm on test-beam data collected with a prototype of the VDET detector is presented. The effect of the detectors misalignment on the Level-1 vertex trigger performance is shown to be a critical issue if the relative position is not controlled better than $100~\mu$m. The Primary vertex resolution on the longitudinal direction obtained on the test-beam for 2D-tracks ($270~\mu$m), translates into a resolution close to $80~\mu$m for the statistics of an LHC event in good agreement with expectations. The discriminating power between B-events and Minimum Bias events is studied using a sample of ``artificial'' events built from events interacting at different targets separated by 1~cm. The results are very encouraging showing the feasibility to trigger on low multiplicity displaced vertices.