Distributions of the signal values in PSB-b for short events with peak amplitudes between 300 and 1000σ in PSB-a (solid line). A random distribution of values in PSB-b is also shown (dot-dashed line). The excess of the solid curve over the dot-dashed curve for amplitudes above 3σ represents about 50% of the total area. Thus, at least 50% percent of the events are in coincidence between PSB-a and PSB-b.