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The liquid argon time projection chamber (LArTPC) detector technology has an excellent capability to measure properties of low-energy neutrinos produced by the sun and supernovae and to look for exotic physics at very low energies. In order to achieve those physics goals, it is crucial to identify and reconstruct signals in the waveforms recorded on each TPC wire. In this paper, we report on a novel algorithm based on a one-dimensional convolutional neural network (CNN) to look for the region-of-interest (ROI) in raw waveforms. We test this algorithm using data from the ArgoNeuT experiment in conjunction with an improved noise mitigation procedure and a more realistic data-driven noise model for simulated events. This deep-learning ROI finder shows promising performance in extracting small signals and gives an efficiency approximately twice that of the traditional algorithm in the low energy region of \\(\\sim\\)0.03-0.1 MeV. This method offers great potential to explore low-energy physics using LArTPCs.

A search for millicharged particles, a simple extension of the standard model, has been performed with the ArgoNeuT detector exposed to the Neutrinos at the Main Injector beam at Fermilab. The ArgoNeuT Liquid Argon Time Projection Chamber detector enables a search for millicharged particles through the detection of visible electron recoils. We search for an event signature with two soft hits (MeV-scale energy depositions) aligned with the upstream target. For an exposure of the detector of \\(1.0\\) \\(\\times\\) \\(10^{20}\\) protons on target, one candidate event has been observed, compatible with the expected background. This search is sensitive to millicharged particles with charges between \\(10^{-3}e\\) and \\(10^{-1}e\\) and with masses in the range from \\(0.1\\) GeV to \\(3\\) GeV. This measurement provides leading constraints on millicharged particles in this large unexplored parameter space region.

We report the first electron neutrino cross section measurements on argon, based on data collected by the ArgoNeuT experiment running in the GeV-scale NuMI beamline at Fermilab. A flux-averaged \\(\\nu_e + \\overline{\\nu}_e\\) total and a lepton angle differential cross section are extracted using 13 \\(\\nu_e\\) and \\(\\overline{\\nu}_e\\) events identified with fully-automated selection and reconstruction. We employ electromagnetic-induced shower characterization and analysis tools developed to identify \\(\\nu_e/\\overline{\\nu}_e\\)-like events among complex interaction topologies present in ArgoNeuT data (\\(\\langle E_{\\bar{\\nu}_e} \\rangle = 4.3\\) GeV and \\(\\langle E_{\\nu_e} \\rangle = 10.5\\) GeV). The techniques are widely applicable to searches for electron-flavor appearance at short- and long-baseline using liquid argon time projection chamber technology. Notably, the data-driven studies of GeV-scale \\(\\nu_e/\\overline{\\nu}_e\\) interactions presented in this Letter probe an energy regime relevant for future DUNE oscillation physics.

MeV-scale energy depositions by low-energy photons produced in neutrino-argon interactions have been identified and reconstructed in ArgoNeuT liquid argon time projection chamber (LArTPC) data. ArgoNeuT data collected on the NuMI beam at Fermilab were analyzed to select isolated low-energy depositions in the TPC volume. The total number, reconstructed energies and positions of these depositions have been compared to those from simulations of neutrino-argon interactions using the FLUKA Monte Carlo generator. Measured features are consistent with energy depositions from photons produced by de-excitation of the neutrino's target nucleus and by inelastic scattering of primary neutrons produced by neutrino-argon interactions. This study represents a successful reconstruction of physics at the MeV-scale in a LArTPC, a capability of crucial importance for detection and reconstruction of supernova and solar neutrino interactions in future large LArTPCs.

We report the first measurement of monoenergetic muon neutrino charged current interactions. MiniBooNE has isolated 236 MeV muon neutrino events originating from charged kaon decay at rest (\\(K^+ \\rightarrow \\mu^+ \\nu_\\mu\\)) at the NuMI beamline absorber. These signal \\(\\nu_\\mu\\)-carbon events are distinguished from primarily pion decay in flight \\(\\nu_\\mu\\) and \\(\\overline{\\nu}_\\mu\\) backgrounds produced at the target station and decay pipe using their arrival time and reconstructed muon energy. The significance of the signal observation is at the 3.9\\(\\sigma\\) level. The muon kinetic energy, neutrino-nucleus energy transfer (\\(\\omega=E_\\nu-E_\\mu\\)), and total cross section for these events is extracted. This result is the first known-energy, weak-interaction-only probe of the nucleus to yield a measurement of \\(\\omega\\) using neutrinos, a quantity thus far only accessible through electron scattering.

The capabilities of liquid argon time projection chambers (LArTPCs) to reconstruct the spatial and calorimetric information of neutrino events have made them the detectors of choice in a number of experiments, specifically those looking to observe electron neutrino (\\(\\nu_e\\)) appearance. The LArTPC promises excellent background rejection capabilities, especially in this \"golden\" channel for both short and long baseline neutrino oscillation experiments. We present the first experimental observation of electron neutrinos and anti-neutrinos in the ArgoNeut LArTPC, in the energy range relevant to DUNE and the Fermilab Short Baseline Neutrino Program. We have selected 37 electron candidate events and 274 gamma candidate events, and measured an 80\\% purity of electrons based on a topological selection. Additionally, we present a of separation of electrons from gammas using calorimetric energy deposition, demonstrating further separation of electrons from background gammas.

The MicroBooNE liquid argon time projection chamber (LArTPC) maintains a high level of liquid argon purity through the use of a filtration system that removes electronegative contaminants in continuously-circulated liquid, recondensed boil off, and externally supplied argon gas. We use the MicroBooNE LArTPC to reconstruct MeV-scale radiological decays. Using this technique we measure the liquid argon filtration system's efficacy at removing radon. This is studied by placing a 500 kBq \\(^{222}\\)Rn source upstream of the filters and searching for a time-dependent increase in the number of radiological decays in the LArTPC. In the context of two models for radon mitigation via a liquid argon filtration system, a slowing mechanism and a trapping mechanism, MicroBooNE data supports a radon reduction factor of greater than 99.999% or 97%, respectively. Furthermore, a radiological survey of the filters found that the copper-based filter material was the primary medium that removed the \\(^{222}\\)Rn. This is the first observation of radon mitigation in liquid argon with a large-scale copper-based filter and could offer a radon mitigation solution for future large LArTPCs.

Primary challenges for current and future precision neutrino experiments using liquid argon time projection chambers (LArTPCs) include understanding detector effects and quantifying the associated systematic uncertainties. This paper presents a novel technique for assessing and propagating LArTPC detector-related systematic uncertainties. The technique makes modifications to simulation waveforms based on a parameterization of observed differences in ionization signals from the TPC between data and simulation, while remaining insensitive to the details of the detector model. The modifications are then used to quantify the systematic differences in low- and high-level reconstructed quantities. This approach could be applied to future LArTPC detectors, such as those used in SBN and DUNE.

We report a measurement of the energy-dependent total charged-current cross section \\(\\sigma\\left(E_\\nu\\right)\\) for inclusive muon neutrinos scattering on argon, as well as measurements of flux-averaged differential cross sections as a function of muon energy and hadronic energy transfer (\\(\\nu\\)). Data corresponding to 5.3\\(\\times\\)10\\(^{19}\\) protons on target of exposure were collected using the MicroBooNE liquid argon time projection chamber located in the Fermilab Booster Neutrino Beam with a mean neutrino energy of approximately 0.8 GeV. The mapping between the true neutrino energy \\(E_\\nu\\) and reconstructed neutrino energy \\(E^{rec}_\\nu\\) and between the energy transfer \\(\\nu\\) and reconstructed hadronic energy \\(E^{rec}_{had}\\) are validated by comparing the data and Monte Carlo (MC) predictions. In particular, the modeling of the missing hadronic energy and its associated uncertainties are verified by a new method that compares the \\(E^{rec}_{had}\\) distributions between data and an MC prediction after constraining the reconstructed muon kinematic distributions, energy and polar angle, to those of data. The success of this validation gives confidence that the missing energy in the MicroBooNE detector is well-modeled and underpins first-time measurements of both the total cross section \\(\\sigma\\left(E_\\nu\\right)\\) and the differential cross section \\(d\\sigma/d\\nu\\) on argon.

We present the first measurement of the single-differential \\(\\nu_e + \\bar{\\nu}_e\\) charged-current inclusive cross sections on argon in electron or positron energy and in electron or positron scattering cosine over the full angular range. Data were collected using the MicroBooNE liquid argon time projection chamber located off-axis from the Fermilab Neutrinos at the Main Injector beam over an exposure of \\(2.0\\times10^{20}\\) protons on target. The signal definition includes a 60 MeV threshold on the \\(\\nu_e\\) or \\(\\bar{\\nu}_e\\) energy and a 120 MeV threshold on the electron or positron energy. The measured total and differential cross sections are found to be in agreement with the GENIE, NuWro, and GiBUU neutrino generators.