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We report the first observation and measurement of antiproton annihilation at rest on argon track and shower multiplicities and particle identification conducted with the LArIAT experiment. Stopping antiprotons from the Fermilab Test Beam Facility’s charged particle test beam are identified using beamline instrumentation and LArIAT’s liquid argon time projection chamber (LArTPC). The charged particle multiplicity from the annihilation vertex is manually evaluated via hand scanning, yielding a mean of $3.2\pm 0.4$tracks and a standard deviation of 1.3 tracks, consistent with a semiautomated reconstruction resulting in $2.8\pm 0.4$tracks and a standard deviation of 1.2 tracks. Both methods are consistent with Monte Carlo simulations within statistical uncertainty. The shower multiplicities and particle identification for outgoing tracks are also consistent with eant4 model predictions. These results, obtained from a low-statistics sample, provide a foundation for higher-statistics studies in larger LArTPCs, which could refine modeling of intranuclear annihilation on argon and inform scenarios such as neutron-antineutron oscillations. 

We report the measurement of the final-state products of negative pion and muon nuclear capture at rest on argon by the LArIAT experiment at the Fermilab Test Beam Facility. We measure a population of isolated MeV-scale energy depositions, or blips, in 296 LArIAT events containing tracks from stopping low-momentum pions and muons. The average numbers of visible blips are measured to be $0.74\pm 0.19$and $1.86\pm 0.17$near muon and pion track endpoints, respectively. The $3.6\sigma$statistically significant difference in blip content between muons and pions provides the first demonstration of a new method of pion-muon discrimination in neutrino liquid argon time projection chamber experiments. LArIAT Monte Carlo simulations predict substantially higher average blip counts for negative muon ( $1.22\pm 0.08$) and pion ( $2.34\pm 0.09$) nuclear captures. We attribute this difference to 4’s inaccurate simulation of the nuclear capture process. 

We present the strongest experimental limits to date on the mixing angle, $\theta$, with which a new scalar particle, $S$, mixes with the Higgs field in the mass range $110\mathrm{MeV}<m_S<155\mathrm{MeV}$. This result uses the MicroBooNE liquid argon time projection chamber to search for decays of these Higgs-portal scalar particles through the $S\to e^{+}{e}^{-}$channel with the decays of kaons in the NuMI neutrino beam acting as the source of the scalar particles. The analysis uses an exposure of $2.01\times {10}^{21}$protons on target of NuMI beam data including periods when the beam focusing system was configured to focus positively charged hadrons and separate periods when negatively charged hadrons were focused. The analysis searches for scalar particles produced from kaons decaying in flight in the beam’s decay volume and at rest in the target and absorber. At $m_S=125\mathrm{MeV}$( $m_S=150\mathrm{MeV}$) we set a limit of $\theta <3.19\times {10}^{-4}$( $\theta <2.79\times {10}^{-4}$) at the 95% confidence level. 

The short-baseline near detector (SBND), the near detector in the short-baseline neutrino program at Fermi National Accelerator Laboratory, is located just 110 m from the booster neutrino beam target. Thanks to this close proximity, relative to its $4\mathrm{m}\times 4\mathrm{m}$front face, neutrinos enter SBND over a range of angles from 0° to approximately 1.6°, enabling the detector to sample variations in the neutrino flux as a function of the angle—a technique known as precision reaction-independent spectrum measurement (PRISM), referred to here as SBND-PRISM. In this paper, we show how muon- and electron-neutrino fluxes vary as a function of the neutrino beam axis angle and how this can be exploited to expand the physics potential of SBND. We make use of a model that predicts an angle-dependent electron-neutrino excess signal to illustrate this effect, such as ${\nu }_{\mu }\to {\nu }_e$oscillations. We present how SBND-PRISM provides a method to add robustness against uncertainties in cross-section modeling and, more generally, uncertainties that do not depend on the spatial position of neutrino interaction inside the detector. The fluxes, along with their associated covariance matrices, are made publicly available with this publication. 

Dark matter detection experiments using liquid argon rely on a precise characterization of the ionization response to nuclear recoils, especially in the keV energy range relevant for light dark matter interactions. In this work, we present a comprehensive analysis that combines new measurements from the ReD setup, part of the DarkSide experimental program, with calibration data from DarkSide-50, as well as results from the ARIS and SCENE experiments. These combined datasets enable improved constraints on atomic screening effects in the modeling of the ionization response of liquid argon to nuclear recoils. The analysis is performed within the Thomas-Imel recombination framework adopted in previous DarkSide studies, and is here further constrained by the inclusion of ReD data, which allow the screening function to be determined from calibration measurements. By including the updated ionization model into the DarkSide-50 analysis framework, we obtain stronger exclusion limits on low-mass weakly interacting massive particle (WIMP) interactions, setting new world-leading constraints in the $1–3\mathrm{GeV}/{\mathrm{c}}^2$WIMP mass range. Finally, we recast the sensitivity projections for the upcoming DarkSide-20k detector, demonstrating a significantly enhanced discovery potential for low-mass dark matter candidates. 

The MicroBooNE experiment is an 85 tonne active mass liquid argon time projection chamber neutrino detector exposed to the on-axis Booster Neutrino Beam at Fermilab. One of MicroBooNE’s physics goals is the precise measurement of neutrino interactions on argon in the 1 GeV energy regime. Building on the capabilities of the MicroBooNE detector, this analysis identifies $K^{+}$mesons, a key signature for the study of strange particle production in neutrino interactions. This measurement is furthermore valuable for background estimation for future nucleon decay searches and for improved reconstruction and particle identification capabilities in experiments such as the Deep Underground Neutrino Experiment. In this Letter, we present the first-ever measurement of a flux-integrated cross section for charged-current muon neutrino induced $K^{+}$production on argon nuclei, determined to be $7.93\pm 3.22\left(\mathrm{stat}\right)\pm 2.83\left(\mathrm{syst}\right)\times {10}^{-42}{\mathrm{cm}}^2/\mathrm{nucleon}$based on an analysis of $6.88\times {10}^{20}$protons on target. This result was found to be consistent with model predictions from different neutrino event generators within the reported uncertainties. 

We present an inclusive search for anomalous production of single-photon events from neutrino interactions in the MicroBooNE experiment. The search and its signal definition are motivated by the previous observation of a low-energy excess of electromagnetic shower events from the MiniBooNE experiment. We use the Wire-Cell reconstruction framework to select a sample of inclusive single-photon final-state interactions with a final efficiency and purity of 7.0% and 40.2%, respectively. We leverage simultaneous measurements of sidebands of charged current ${\nu }_{\mu }$interactions and neutral current interactions producing ${\pi }^0$mesons to constrain signal and background predictions and reduce uncertainties. We perform a blind analysis using a dataset collected from February 2016 to July 2018, corresponding to an exposure of $6.34\times {10}^{20}$protons on target from the Booster Neutrino Beam at Fermilab. In the full signal region, we observe agreement between the data and the prediction, with a goodness-of-fit $p$value of 0.11. We then isolate a subsample of these events containing no visible protons, and observe $93\pm 22\left(\mathrm{stat}\right)\pm 35\left(\mathrm{syst}\right)$data events above prediction, corresponding to just above $2\sigma$local significance, concentrated at shower energies below 600 MeV. 

Abstract The existence of three distinct neutrino flavours,ν_e,ν_μandν_τ, is a central tenet of the Standard Model of particle physics^1,2. Quantum-mechanical interference can allow a neutrino of one initial flavour to be detected sometime later as a different flavour, a process called neutrino oscillation. Several anomalous observations inconsistent with this three-flavour picture have motivated the hypothesis that an additional neutrino state exists, which does not interact directly with matter, termed as ‘sterile’ neutrino,ν_s(refs. ^3–9). This includes anomalous observations from the Liquid Scintillator Neutrino Detector (LSND)³experiment and Mini-Booster Neutrino Experiment (MiniBooNE)^4,5, consistent withν_μ → ν_etransitions at a distance inconsistent with the three-neutrino picture. Here we use data obtained from the MicroBooNE liquid-argon time projection chamber¹⁰in two accelerator neutrino beams to exclude the single light sterile neutrino interpretation of the LSND and MiniBooNE anomalies at the 95% confidence level (CL). Moreover, we rule out a notable portion of the parameter space that could explain the gallium anomaly^6–8. This is one of the first measurements to use two accelerator neutrino beams to break a degeneracy betweenν_eappearance and disappearance, which would otherwise weaken the sensitivity to the sterile neutrino hypothesis. We find no evidence for eitherν_μ → ν_eflavour transitions orν_edisappearance that would indicate non-standard flavour oscillations. Our results indicate that previous anomalous observations consistent withν_μ → ν_etransitions cannot be explained by introducing a single sterile neutrino state. 

We report results from an updated search for neutral current (NC) resonant $\mathrm{\Delta }\left(1232\right)$baryon production and subsequent $\mathrm{\Delta }$radiative decay (NC $\mathrm{\Delta }\to N\gamma$). We consider events with and without final state protons; events with a proton can be compared with the kinematics of a $\mathrm{\Delta }\left(1232\right)$baryon decay, while events without a visible proton represent a more generic phase space. In order to maximize sensitivity to each topology, we simultaneously make use of two different reconstruction paradigms, Pandora and Wire-Cell, which have complementary strengths, and select mostly orthogonal sets of events. Considering an overall scaling of the NC $\mathrm{\Delta }\to N\gamma$rate as an explanation of the MiniBooNE anomaly, our data exclude this hypothesis at 94.4% CL. When we decouple the expected correlations between NC $\mathrm{\Delta }\to N\gamma$events with and without final state protons, our data exclude an interpretation in which all excess events have associated protons at $2.0\sigma$, and are consistent with an interpretation in which all excess events have no associated protons at  $0.63\sigma$. 

We report a new measurement of flux-integrated differential cross sections for charged-current (CC) muon neutrino interactions with argon nuclei that produce no final-state pions ( ${\nu }_{\mu }\mathrm{CC}0\pi$). These interactions are of particular importance as a topologically defined signal dominated by quasielasticlike interactions. This measurement was performed with the MicroBooNE liquid argon time projection chamber detector located at the Fermilab Booster Neutrino Beam and uses an exposure of $1.3\times {10}^{21}$protons on target collected between 2015 and 2020. The results are presented in terms of single- and double-differential cross sections as a function of the final-state muon momentum and angle. The data are compared with widely used neutrino event generators. We find good agreement with the single-differential measurements, while only a subset of generators are also able to adequately describe the data in double-differential distributions. This work facilitates comparison with Cherenkov detector measurements, including those located at the Booster Neutrino Beam.