  The ICARUS-T600 detector is a 760-ton Liquid Argon Time Projection Chamber
(LArTPC) currently operating at Fermilab as the Far Detector in the Short
Baseline Neutrino (SBN) program. The SBN program is composed of three LArTPCs
with a central goal of testing the sterile neutrino hypothesis. After operating
for 3-years in the Gran Sasso Underground Laboratory, the ICARUS detector was
shipped to CERN where it was outfitted with 360 8" Photomultiplier Tubes (PMTs)
for a new optical detection system. The PMT system detects fast scintillation
light from charged particles interacting in the Liquid Argon, generating the
trigger signal for the full detector and allows 3D reconstruction of events.
Now operating at shallow depth, the detector is exposed to a high flux of
cosmic rays that can fake neutrino interactions. To mitigate this effect a
Cosmic Ray Tagger (CRT) and a 3-meter-thick concrete were installed. Precise
timing information from both the PMT and CRT subsystems can help to identify
whether an interaction originated from inside or outside of the ICARUS
cryostat. This paper reviews a method for cosmogenic background reduction and
timing calibration of the CRT and PMT light detection systems in ICARUS.
