The MicroBooNE detector is a liquid argon time projection chamber at Fermilab
designed to study short-baseline neutrino oscillations and neutrino-argon
interaction cross-section. Due to its location near the surface, a good
understanding of cosmic muons as a source of backgrounds is of fundamental
importance for the experiment. We present a method of using an external 0.5 m
(L) x 0.5 m (W) muon counter stack, installed above the main detector, to
determine the cosmic-ray reconstruction efficiency in MicroBooNE. Data are
acquired with this external muon counter stack placed in three different
positions, corresponding to cosmic rays intersecting different parts of the
detector. The data reconstruction efficiency of tracks in the detector is found
to be ϵdata​=(97.1±0.1 (stat)±1.4 (sys))%, in good agreement with the Monte Carlo reconstruction
efficiency ϵMC​=(97.4±0.1)%. This analysis represents
a small-scale demonstration of the method that can be used with future data
coming from a recently installed cosmic-ray tagger system, which will be able
to tag ≈80% of the cosmic rays passing through the MicroBooNE
detector.Comment: 19 pages, 12 figure