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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. 

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. 

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. 

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 present MicroBooNE’s first search for dark sector $e^{+}{e}^{-}$explanations of the long-standing MiniBooNE anomaly. The MiniBooNE anomaly has garnered significant attention over the past 20 years including previous MicroBooNE investigations into both anomalous electron and photon excesses, but its origin still remains unclear. In this Letter, we provide the first direct test of dark sector models in which dark neutrinos, produced through neutrino-induced scattering, decay into missing energy and visible $e^{+}{e}^{-}$pairs comprising the MiniBooNE anomaly. Many such models have recently gained traction as a viable solution to the anomaly while evading past bounds. Using an exposure of $6.87\times {10}^{20}$protons-on-target in the Booster Neutrino Beam, we implement a selection targeting forward-going, coherently produced $e^{+}{e}^{-}$events. After unblinding, we observe 95 events, which we compare with the constrained background-only prediction of $69.7\pm 17.3$. This analysis sets the world’s first direct limits on these dark sector models and, at the 95% confidence level, excludes the entirety of the single dark neutrino and majority of the dual dark neutrino, parameter space that is viable as a solution to the MiniBooNE anomaly.