First combined beam-time test of PXD and SVD Modules at DESY

The VerteX Detector (VXD) system of Belle II is critical to reconstruct the vertices of short-lived particles with lifetimes of around one trillionth of a second. The Belle II VXD consists of two inner layers of a DEPFET-based silicon PiXel Detector (PXD) followed by four layers of a Silicon Vertex Detector (SVD), composed of double sided silicon strips. During the month of April 2016 the PXD, SVD and Belle II DAQ teams worked together in a beam test that was carried out at Deutsches Elektronen-Synchrotron DESY(Hamburg, Germany). For the first time, using one segment of each PXD and SVD layer, a slice of the whole Belle II VXD was assembled and tested under realistic conditions. DESY provided an electron beam with energy up to 6 GeV and a solenoid magnet with a field of 1 T. The two teams, made up of a total of 66 people from 10 different countries and 4 continents, verified the integration between the PXD and VXD and evaluated the performance of the sensors in terms of efficiency and resolution. The test also provided an opportunity to evaluate the CO2 cooling system and the monitoring and environmental sensors, as well as the data acquisition system and the software alignment and tracking algorithms. The figure shows prototypes of the PXD (top left) and the SVD (top right) before the beam test as well as the combined system entering the solenoid magnet.

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