91̽��

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 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.

Abstract:

We present flux-integrated charged-current ${\nu }_{\mu }$ cross-section measurements on argon for final states containing exactly one ${\pi }^{\pm }$ and no other hadrons except nucleons. The analysis uses data from the MicroBooNE experiment in the Booster Neutrino Beam, corresponding to $1.11\times {10}^{21}$ protons on target. Total and single-differential cross-section measurements are provided within a phase space restricted to muon momenta above 150 MeV, pion momenta above 100 MeV, and muon-pion opening angles smaller than 2.65 rad. Differential cross sections are reported with respect to the scattering angles of the muon and pion relative to the beam direction, their momenta, and their combined opening angle. The differential cross section with respect to muon momentum is based on a subset of selected events with the muon track fully contained in the detector, whereas the cross section with respect to pion momentum is based on a subset of selected events rich in pions that have not hadronically scattered on the argon before coming to rest. The latter has not been measured on argon before. The total cross section is measured as $(3.75\pm 0.07(\mathrm{stat})\pm 0.80(\mathrm{syst}))\times {10}^{-38}{\mathrm{cm}}^2/\mathrm{Ar}$ at a mean energy of approximately 0.8 GeV. Comparisons of the measured cross sections with predictions from multiple neutrino-nucleus interaction generators show good overall agreement, except at very forward muon angles.

Abstract:

Bayesian analysis results require a choice of prior distribution. In long-baseline neutrino oscillation physics, the usual parameterisation of the mixing matrix induces a prior that privileges certain neutrino mass and flavour state symmetries. Here we study the effect of privileging alternate symmetries on the results of the T2K experiment. We find that constraints on the level of CP violation (as given by the Jarlskog invariant) are robust under the choices of prior considered in the analysis. On the other hand, the degree of octant preference for the atmospheric angle depends on which symmetry has been privileged.

Abstract:

Charged-current neutrino interactions with final states containing zero mesons and at least one proton are of high interest for current and future accelerator-based neutrino oscillation experiments. Using the Booster Neutrino Beam and the MicroBooNE detector at Fermi National Accelerator Laboratory, we have obtained the first double-differential cross-section measurements of this channel for muon neutrino scattering on an argon target with a leading proton momentum threshold of $0.25\mathrm{GeV}/c$ . We also report a flux-averaged total cross section of $\sigma =(11.8\pm 1.2)\times {10}^{-38}{\mathrm{cm}}^2/\mathrm{Ar}$ and several single-differential measurements which extend and improve upon previous results. Statistical and systematic uncertainties are quantified with a full treatment of correlations across 359 kinematic bins, including correlations between distributions describing different observables. The resulting dataset provides the most detailed information obtained to date for testing models of mesonless neutrino-argon scattering.

Abstract:

We present the first measurement of differential cross sections for charged-current muon neutrino interactions on argon with one muon, two protons, and no pions in the final state. These final states are dominated by two-nucleon knockout interactions, which are complicated to model and for which there is currently limited information about the characteristics of these interactions in existing neutrino-nucleus scattering data. Detailed investigations of two-nucleon knockout are vital to 91̽�� upcoming experiments exploring the nature of the neutrino. Among the different kinematic quantities measured, the opening angle between the two protons, the angle between the total proton momentum and the muon, and the total transverse momentum of the final state system are most sensitive to the underlying physics processes as embodied in various theoretical models.