Dr Patrick Green

Abstract:

The Deep Underground Neutrino Experiment (DUNE) is a next-generation neutrino experiment with a rich physics program that includes searches for the hypothetical phenomenon of proton decay. Utilizing liquid-argon time-projection chamber technology, DUNE is expected to achieve world-leading sensitivity in the proton decay channels that involve charged kaons in their final states. The first DUNE demonstrator, ProtoDUNE Single-Phase, was a 0.77 kt detector that operated from 2018 to 2020 at the CERN Neutrino Platform, exposed to a mixed hadron and electron test-beam with momenta ranging from 0.3 to $7\mathrm{GeV}/\mathrm{c}$ . We present a selection of low-energy kaons among the secondary particles produced in hadronic reactions, using data from the 6 and $7\mathrm{GeV}/\mathrm{c}$ beam runs. The selection efficiency is 1% and the sample purity 92%. The initial energies of the selected kaon candidates encompass the expected energy range of kaons originating from proton decay events in DUNE (below $\sim 200\mathrm{MeV}$ ). In addition, we demonstrate the capability of this detector technology to discriminate between kaons and other particles such as protons and muons, and provide a comprehensive description of their energy loss in liquid argon, which shows good agreement with the simulation. These results pave the way for future proton decay searches at DUNE.

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:

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 $7.93\pm 3.22(\mathrm{stat})\pm 2.83(\mathrm{syst})\times {10}^{-42}{\mathrm{cm}}^2/\mathrm{nucleon}$ 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, 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.