  The Deep Underground Neutrino Experiment (DUNE) together with the Long
Baseline Neutrino Facility (LBNF) hosted at the Fermilab will provide a unique,
world-leading program for the exploration of key questions at the forefront of
neutrino physics and astrophysics. CP violation in neutrino flavor mixing is
one of its most important potential discoveries. Additionally, the experiment
will determine the neutrino mass hierarchy and precisely measure the neutrino
mixing parameters which may potentially reveal new fundamental symmetries of
nature. Moreover, the DUNE is also designed for the observation of nucleon
decay and supernova burst neutrinos. The photon detection (PD) system in the
DUNE far detector provides trigger for cosmic backgrounds, enhances supernova
burst trigger efficiency and improves the energy resolution of the detector.
The DUNE adopts the technology of liquid argon time projection chamber (LArTPC)
that requires the PD sensors, silicon photomultipliers (SiPM), to be carefully
chosen to not only work properly in cryostat, but also meet certain
specifications for the life of the experiment. A comprehensive testing of SiPMs
in cryostat is necessary since the datasheet provided by the manufactures in
the market does not cover this temperature regime. This paper gives the
detailed characterization results of SenSL C-Series 60035 SiPMs, including
gain, dark count rate (DCR), cross-talk and after-pulse rate. Characteristic
studies on SiPMs from other vendors are also discussed in order to avoid any
potential problems associated with using a single source. Moreover, the results
of the ongoing mechanical durability tests are shown for the current candidate,
SenSL B/C-Series 60035 SiPMs.
