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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.

A bstract The MicroBooNE liquid argon time projection chamber located at Fermilab is a neutrino experiment dedicated to the study of short-baseline oscillations, the measurements of neutrino cross sections in liquid argon, and to the research and development of this novel detector technology. Accurate and precise measurements of calorimetry are essential to the event reconstruction and are achieved by leveraging the TPC to measure deposited energy per unit length along the particle trajectory, with mm resolution. We describe the non-uniform calorimetric reconstruction performance in the detector, showing dependence on the angle of the particle trajectory. Such non-uniform reconstruction directly affects the performance of the particle identification algorithms which infer particle type from calorimetric measurements. This work presents a new particle identification method which accounts for and effectively addresses such non-uniformity. The newly developed method shows improved performance compared to previous algorithms, illustrated by a 93.7% proton selection efficiency and a 10% muon mis-identification rate, with a fairly loose selection of tracks performed on beam data. The performance is further demonstrated by identifying exclusive final states in ν μ CC interactions. While developed using MicroBooNE data and simulation, this method is easily applicable to future LArTPC experiments, such as SBND, ICARUS, and DUNE.

A significant challenge in measurements of neutrino oscillations is reconstructing the incoming neutrino energies. While modern fully-active tracking calorimeters such as liquid argon time projection chambers in principle allow the measurement of all final state particles above some detection threshold, undetected neutrons remain a considerable source of missing energy with little to no data constraining their production rates and kinematics. We present the first demonstration of tagging neutrino-induced neutrons in liquid argon time projection chambers using secondary protons emitted from neutron-argon interactions in the MicroBooNE detector. We describe the method developed to identify neutrino-induced neutrons and demonstrate its performance using neutrons produced in muon-neutrino charged current interactions. The method is validated using a small subset of MicroBooNE’s total dataset. The selection yields a sample with 60 % of selected tracks corresponding to neutron-induced secondary protons. At this purity, the integrated efficiency is 8.4% for neutrons that produce a detectable proton.

We report the first double-differential neutrino-argon cross section measurement made simultaneously for final states with and without protons for the inclusive muon neutrino charged-current interaction channel. The proton kinematics of this channel are further explored with a differential cross section measurement as a function of the leading proton's kinetic energy that extends across the detection threshold. These measurements utilize data collected using the MicroBooNE detector from 6.4\\(\\times10^{20}\\) protons on target from the Fermilab Booster Neutrino Beam with a mean neutrino energy of \\(\\sim\\)0.8 GeV. Extensive data-driven model validation utilizing the conditional constraint formalism is employed. This motivates enlarging the uncertainties with an empirical reweighting approach to minimize the possibility of extracting biased cross section results. The extracted nominal flux-averaged cross sections are compared to widely used event generator predictions revealing severe mismodeling of final states without protons for muon neutrino charged-current interactions, possibly from insufficient treatment of final state interactions. These measurements provide a wealth of new information useful for improving event generators which will enhance the sensitivity of precision measurements in neutrino experiments.

We report measurements of radon progeny in liquid argon within the MicroBooNE time projection chamber (LArTPC). The presence of specific radon daughters in MicroBooNE's 85 metric tons of active liquid argon bulk is probed with newly developed charge-based low-energy reconstruction tools and analysis techniques to detect correlated \\(^{214}\\)Bi-\\(^{214}\\)Po radioactive decays. Special datasets taken during periods of active radon doping enable new demonstrations of the calorimetric capabilities of single-phase neutrino LArTPCs for \\(\\beta\\) and \\(\\alpha\\) particles with electron-equivalent energies ranging from 0.1 to 3.0 MeV. By applying \\(^{214}\\)Bi-\\(^{214}\\)Po detection algorithms to data recorded over a 46-day period, no statistically significant presence of radioactive \\(^{214}\\)Bi is detected, and a limit on the activity is placed at \\(<0.35\\) mBq/kg at the 95% confidence level. This bulk \\(^{214}\\)Bi radiopurity limit -- the first ever reported for a liquid argon detector incorporating liquid-phase purification -- is then further discussed in relation to the targeted upper limit of 1 mBq/kg on bulk \\(^{222}\\)Rn activity for the DUNE neutrino detector.

We present a search for long-lived Higgs portal scalars (HPS) and heavy neutral leptons (HNL) decaying in the MicroBooNE liquid-argon time projection chamber. The measurement is performed using data collected synchronously with the NuMI neutrino beam from Fermilab's Main Injector with a total exposure corresponding to \\(7.01 \\times 10^{20}\\) protons on target. We set upper limits at the \\(90\\%\\) confidence level on the mixing parameter \\(\\lvert U_{\\mu 4}\\rvert^2\\) ranging from \\(\\lvert U_{\\mu 4}\\rvert^2<12.9\\times 10^{-8}\\) for Majorana HNLs with a mass of \\(m_{\\rm HNL}=246\\) MeV to \\(\\lvert U_{\\mu 4}\\rvert^2<0.92 \\times 10^{-8}\\) for \\(m_{\\rm HNL}=385\\) MeV, assuming \\(\\lvert U_{e 4}\\rvert^2 = \\lvert U_{\\tau 4}\\rvert^2 = 0\\) and HNL decays into \\(\\mu^\\pm\\pi^\\mp\\) pairs. These limits on \\(\\lvert U_{\\mu 4}\\rvert^2\\) represent an order of magnitude improvement in sensitivity compared to the previous MicroBooNE result. We also constrain the scalar-Higgs mixing angle \\(\\theta\\) by searching for HPS decays into \\(\\mu^+\\mu^-\\) final states, excluding a contour in the parameter space with lower bounds of \\(\\theta^2<31.3 \\times 10^{-9}\\) for \\(m_{\\rm HPS}=212\\) GeV and \\(\\theta^2<1.09 \\times 10^{-9}\\) for \\(m_{\\rm HPS}=275\\) GeV. These are the first constraints on the scalar-Higgs mixing angle \\(\\theta\\) from a dedicated experimental search in this mass range.

We present a search for eV-scale sterile neutrino oscillations in the MicroBooNE liquid argon detector, simultaneously considering all possible appearance and disappearance effects within the \\(3+1\\) active-to-sterile neutrino oscillation framework. We analyze the neutrino candidate events for the recent measurements of charged-current \\(\\nu_e\\) and \\(\\nu_{\\mu}\\) interactions in the MicroBooNE detector, using data corresponding to an exposure of 6.37\\(\\times\\)10\\(^{20}\\) protons on target from the Fermilab booster neutrino beam. We observe no evidence of light sterile neutrino oscillations and derive exclusion contours at the \\(95\\%\\) confidence level in the plane of the mass-squared splitting \\(\\Delta m^2_{41}\\) and the sterile neutrino mixing angles \\(\\theta_{\\mu e}\\) and \\(\\theta_{ee}\\), excluding part of the parameter space allowed by experimental anomalies. Cancellation of \\(\\nu_e\\) appearance and \\(\\nu_e\\) disappearance effects due to the full \\(3+1\\) treatment of the analysis leads to a degeneracy when determining the oscillation parameters, which is discussed in this paper and will be addressed by future analyses.

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.