Dr Patrick Green

Abstract:

The existence of three distinct neutrino flavours, νe, νμ and ντ, is a central tenet of the Standard Model of particle physics1,2. 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, νs (refs. 3, 4, 5, 6, 7, 8–9). This includes anomalous observations from the Liquid Scintillator Neutrino Detector (LSND)3 experiment and Mini-Booster Neutrino Experiment (MiniBooNE)4,5, consistent with νμ → νe transitions at a distance inconsistent with the three-neutrino picture. Here we use data obtained from the MicroBooNE liquid-argon time projection chamber10 in 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 anomaly6, 7–8. This is one of the first measurements to use two accelerator neutrino beams to break a degeneracy between νe appearance and disappearance, which would otherwise weaken the sensitivity to the sterile neutrino hypothesis. We find no evidence for either νμ → νe flavour transitions or νe disappearance that would indicate non-standard flavour oscillations. Our results indicate that previous anomalous observations consistent with νμ → νe transitions cannot be explained by introducing a single sterile neutrino state.

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 support 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.

Abstract:

We report results from an updated search for neutral current (NC) resonant $\mathrm{\Delta }(1232)$ 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 $\mathrm{\Delta }(1232)$ 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  $0.63\sigma$ .

Abstract:

We report the measurement of the triple-differential cross section d 3 σ / d E vis d cos ( θ μ ) d P μ for inclusive muon-neutrino charged-current scattering on argon. This measurement utilizes data from 6.4 × 10 20 protons on target of exposure collected using the MicroBooNE liquid argon time projection chamber located along the Fermilab Booster Neutrino Beam with a mean neutrino energy of approximately 0.8 GeV. The mapping from reconstructed kinematics to truth quantities is validated within uncertainties by comparing the distribution of reconstructed hadronic energy in data to that of the model prediction in different muon scattering angle bins after applying a conditional constraint from the muon momentum distribution in data. The success of this validation provides confidence that the energy transfer in the MicroBooNE detector is well-modeled within simulation uncertainties, enabling a reliable unfolding to a triple-differential cross section defined at the nominal neutrino flux over muon momentum, muon scattering angle, and visible neutrino energy. This validation not only supports accurate cross-section extraction, but also establishes a critical foundation for tuning interaction models used in future neutrino oscillation measurements. The unfolded measurement covers an extensive phase space, providing a wealth of information useful for future liquid argon time projection chamber experiments measuring neutrino oscillations. Comparisons against a number of commonly used model predictions are included and their performance in different parts of the available phase-space is discussed.