CERN Accelerating science

Beam detectors

A set of scintillation and Cherenkov counters as well as the beam position detectors located upstream of the target provide precise timing reference, along with charge and position measurement of the incoming beam particles. Interaction counters located downstream of the target allows to trigger on interactions in the target. The first detector S1 is located upstream of the target at position z = -36.42m. As the time of flight resolution in low-multiplicity events has to rely on a precise reference time, the S1 counter (0.5cm thick) is equipped with four photomultipliers directly coupled to the scintillator. The second beam counter S2 (0.2cm thick) is located just behind the BPD-2 detector at z = -14.42m. Downstream of the S2 detector, two 1cm thick veto scintillator detectors V0 and V1 are positioned at z = -14.16m and z = -6.72m. The round V0 detector has outer diameter of 8cm and in the center a hole of 1cm diameter. The square (10 x 10cm2) V1 detector also has a 1cm central hole. The S4 and S5 detectors (2cm diameter, 0.5cm thickness) are located downstream of the target at z = -2.11m and 9.80m. They are used to select interactions of beam particles in the target. Interactions in the target are signaled by the absence of the beam particle signal in the counter. Three Beam Position Detectores are placed along the beamline upstream of the target in oreder to measure the position of icoming particles in the transverse plane. These detectors are proportional chambers of 48 x 48 mm2 of active areas, operating with Ar/CO2 85/15 gas mixture. Each BPD measures the position of the trigger-selected beam particle in two orthogonal directions independently using two planes of orthogonal strips. On each strip plane a charge distribution is induced with a width of about 5 strips on average.