The High Granularity Timing Detector (HGTD) will be
installed in the ATLAS detector to mitigate pile-up effects during
the High Luminosity (HL) upgrade of the Large Hadron Collider (LHC)
at CERN. The design of the HGTD is based on the use of Low Gain
Avalanche Detectors (LGADs), with an active thickness of
50 μm, that allow to measure with high-precision the time of
arrival of particles. The HGTD will improve the particle-vertex
assignment by measuring the track time with a resolution ranging
from approximately 30 ps at the beginning of the HL-LHC operations
to 50 ps at the end. Performances of several unirradiated, as well
as neutron- and proton-irradiated, LGAD sensors from different
vendors have been measured in beam test campaigns during the years
2018 and 2019 at CERN SPS and DESY. This paper presents the results
obtained with data recorded by an oscilloscope synchronized with a
beam telescope which provides particle position information within a
resolution of a few μm. Collected charge, time resolution and
hit efficiency are presented. In addition to these properties, the
charge uniformity is also studied as a function of the position of
the incident particle inside the sensor pad.
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