Simulations and Data analysis for the 35 ton Liquid Argon detector as a prototype for the DUNE experiment

The Deep Underground Neutrino Experiment (DUNE) is a next-generation neutrino experiment
which will be built at the Sanford Underground Research Facility (SURF), and will
receive a wide-band neutrino beam from Fermilab, 1300 km away. At this baseline DUNE
will be able to study many of the properties of neutrino mixing, including the neutrino mass
hierarchy and the value of the CP-violating complex phase (δCP). DUNE will utilise Liquid
Argon (LAr) Time Projection Chamber (TPC) (LArTPC) technology, and the Far Detector
(FD) will consist of four modules, each containing 17.1 kt of LAr with a fiducial mass of
around 10 kt. Each of these FD modules represents around an order of magnitude increase in
size, when compared to existing LArTPC experiments.
The 35 ton detector is the first DUNE prototype for the single (LAr) phase design of the
FD. There were two running periods, one from November 2013 to February 2014, and a
second from November 2015 to March 2016. During the second running period, a system of
TPCs was installed, and cosmic-ray data were collected. A method of particle identification
was developed using simulations, though this was not applied to the data due to the higher
than expected noise level. A new method of determining the interaction time of a track, using
the effects of longitudinal diffusion, was developed using the cosmic-ray data. A camera
system was also installed in the detector for monitoring purposes, and to look for high voltage
breakdowns.
Simulations concerning the muon-induced background rate to nucleon decay are performed,
following the incorporation of the MUon Simulations UNderground (MUSUN)
generator into the DUNE software framework. A series of cuts which are based on Monte
Carlo truth information is developed, designed to reject simulated background events, whilst
preserving simulated signal events in the n→K++e− decay channel. No background events
are seen to survive the application of these cuts in a sample of 2 × 109 muons, representing
401.6 years of detector live time. This corresponds to an annual background rate of
< 0.44 events·Mt−1·year−1 at 90% confidence, using a fiducial mass of 13.8 kt.