Design and integration of a SiPM based Timing Reference for ATLAS HGTD test beam

For the upcoming high luminosity upgrade of the LHC, CERN is considering the addition of the High Granularity Timing Detector (HGTD) in front of the end cap and forward calorimeters of ATLAS detector to mitigate pile-up effects. Low Gain Avalanche Diodes (LGADs) are the technology of choice for this timing application. Several test beam campaigns are performed to evaluate sensor performance. A Silicon Photomultiplier (SiPM) coupled to a quartz crystal is used as a timing reference, providing resolutions < 20 ps. A new readout and support board was developed for the upcoming test beam campaigns along with a 3D printed light-tight enclosure and support structure. The design, fabrication and assembly of the new timing reference system are presented.