First Search for Dark Sector $e^+e^-$ Explanations of the MiniBooNE Anomaly at MicroBooNE (2502.10900v1)

Abstract: 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 majority of the parameter space viable as a solution to the MiniBooNE anomaly.

• The paper conducts the world's first search using MicroBooNE data for dark sector explanations of the MiniBooNE anomaly, focusing on dark neutrino decays into electron-positron pairs.
• The analysis observed 95 candidate events, consistent with the predicted background of 69.7 ± 17.3 events, showing a modest 1.5σ deviation from the background expectation.
• This research sets the world's first exclusion limits on previously unconstrained dark sector models, ruling out most solutions proposed to explain the MiniBooNE anomaly at a 95% confidence level.

Exploration of Dark Sector Explanations for the MiniBooNE Anomaly Using MicroBooNE

The research presented addresses the enigmatic MiniBooNE anomaly through an investigation using the MicroBooNE detector, which is situated at Fermilab in the Booster Neutrino Beam. The notable MiniBooNE anomaly, linked to an unexpected excess of electron-like events observed at a 1 GeV neutrino beam, has puzzled the scientific community for over two decades. Potentially indicative of physics beyond the Standard Model (BSM), this anomaly has yet to be explained satisfactorily by conventional hypotheses involving underestimated backgrounds or systematic uncertainties.

In this paper, the authors embark on a pioneering exploration of "dark sector" explanations, specifically focusing on scenarios where dark neutrinos, generated through neutrino-nucleus interactions, decay into both missing energy and visible electron-positron ($e^+e^-$) pairs. This approach is unique as it attempts to directly test dark sector models using data derived from the MicroBooNE experiment, offering possible solutions to the MiniBooNE anomaly while evading previous constraints.

MicroBooNE's experimental setup utilizes an active volume of liquid argon in a time projection chamber, capturing the intricacies of the neutrino-induced processes. The research specifically targets coherent scattering events resulting in forward-going dark neutrinos, a predominantly unexplored hypothesis of the MiniBooNE anomaly. This focus is supported by theoretical models suggesting that these dark neutrinos decay via a dark gauge boson ($Z^\prime$) within the detector's active volume, producing the $e^+e^-$ signature in question.

With an exposure of $6.87 \times 10^{20}$ protons-on-target, the researchers documented 95 candidate events, which were thoroughly compared to the constrained background prediction of $69.7 \pm 17.3$ events. This observed result aligns with the background expectations, resulting in a modest 1.5σ deviation, thus challenging the presence of hypothesized signals within the investigated parameter space.

Additionally, the researchers employed comprehensive simulation frameworks, notably the DarkNews generator, punctuated by the integration of GENIE, to accommodate variability across model parameters related to both single and dual dark neutrino scenarios. These simulations were pivotal in detailing coherent scattering kinematics and subsequent decay processes that could potentially manifest as $e^+e^-$ events within MicroBooNE.

A notable achievement of this paper is the introduction of world's first exclusion limits on treated dark sector models, as delineated by new constraints spanning a broad parameter space and governed by variables such as the dark gauge boson mass and $e^+e^-$ decay signatures. These exclusions rule out the majority of dark sector solutions that could previously account for the MiniBooNE anomaly at a 95% confidence level.

In summary, this research provides critical insights into dark sector explorations and addresses longstanding ambiguities associated with the MiniBooNE anomaly. The analysis not only constrains the parameter scope of these novel models but also emphasizes the potential of neutrino experiments as viable probes for unveiling BSM physics. Future endeavors might investigate alternative dark sector interactions, possibly involving scalar mediators or non-coherent scattering scenarios, further leveraging the capacities of the LArTPC detectors to decipher new physics paradigms.