Dr Kirsty Duffy

Abstract:

We present a set of new generalized kinematic imbalance variables that can be measured in neutrino scattering. These variables extend previous measurements of kinematic imbalance on the transverse plane and are more sensitive to modeling of nuclear effects. We demonstrate the enhanced power of these variables using simulation and then use the MicroBooNE detector to measure them for the first time. We report flux-integrated single- and double-differential measurements of charged-current muon neutrino scattering on argon using a topology with one muon and one proton in the final state as a function of these novel kinematic imbalance variables. These measurements allow us to demonstrate that the treatment of charged current quasielastic interactions in genie version 2 is inadequate to describe data. Further, they reveal tensions with more modern generator predictions particularly in regions of phase space where final state interactions are important.

Abstract:

We report a search for an anomalous excess of inclusive charged-current (CC) νe interactions using the Wire-Cell event reconstruction package in the MicroBooNE experiment, which is motivated by the previous observation of a low-energy excess (LEE) of electromagnetic events from the MiniBooNE experiment. With a single liquid argon time projection chamber detector, the measurements of νµ CC interactions as well as π 0 interactions are used to constrain signal and background predictions of νe CC interactions. A data set collected from February 2016 to July 2018 corresponding to an exposure of 6.369 × 1020 protons on target from the Booster Neutrino Beam at FNAL is analyzed. With x representing an overall normalization factor and referred to as the LEE strength parameter, we select 56 fully contained νe CC candidates while expecting 69.6 ± 8.0 (stat.) ± 5.0 (sys.) and 103.8 ± 9.0 (stat.) ± 7.4 (sys.) candidates after constraints for the absence (eLEEx=0) of the median signal strength derived from the MiniBooNE observation and the presence (eLEEx=1) of that signal strength, respectively. Under a nested hypothesis test using both rate and shape information in all available channels, the best-fit x is determined to be 0 (eLEEx=0) with a 95.5% confidence level upper limit of x at 0.502. Under a simple-vs-simple hypotheses test, the eLEEx=1 hypothesis is rejected at 3.75σ, while the eLEEx=0 hypothesis is shown to be consistent with the observation at 0.45σ. In the context of the eLEE model, the estimated 68.3% confidence interval of the νe CC hypothesis to explain the LEE observed in the MiniBooNE experiment is disfavored at a significance level of more than 2.6σ (3.0σ) considering MiniBooNE’s full (statistical) uncertainties.

Abstract:

This article presents a measurement of νe interactions without pions in the final state using the MicroBooNE experiment and an investigation into the excess of low-energy electromagnetic events observed by the MiniBooNE collaboration. The measurement is performed in exclusive channels with (1eNp0π) and without (1e0p0π) visible final-state protons using 6.86×1020 protons on target of data collected from the Booster Neutrino Beam at Fermilab. Events are reconstructed with the Pandora pattern recognition toolkit and selected using additional topological information from the MicroBooNE liquid argon time projection chamber. Using a goodness-of-fit test the data are found to be consistent with the predicted number of events with nominal flux and interaction models with a p-value of 0.098 in the two channels combined. A model based on the low-energy excess observed in MiniBooNE is introduced to quantify the strength of a possible νe excess. The analysis suggests that, if an excess is present, it is not consistent with a scaling of the νe contribution to the flux as predicted by the signal model used in the analysis. Combined, the 1eNp0π and 1e0p0π channels do not give a conclusive indication about the tested model, but separately they both disfavor the lowenergy excess model at >90% CL. The observation in the most sensitive 1eNp0π channel is below the prediction and consistent with no excess. In the less sensitive 1e0p0π channel the observation at low energy is above the prediction, while overall there is agreement over the full energy spectrum.

Abstract:

We present a measurement of the ν e -interaction rate in the MicroBooNE detector that addresses the observed MiniBooNE anomalous low-energy excess (LEE). The approach taken isolates neutrino interactions consistent with the kinematics of charged-current quasielastic (CCQE) events. The topology of such signal events has a final state with one electron, one proton, and zero mesons ( 1 e 1 p ). Multiple novel techniques are employed to identify a 1 e 1 p final state, including particle identification that use two methods of Deep-Learning-based image identification and event isolation using a boosted decision-tree ensemble trained to recognize two-body scattering kinematics. This analysis selects 25 ν e -candidate events in the reconstructed neutrino energy range of 200–1200 MeV, while 29.0 ± 1. 9 ( sys ) ± 5. 4 ( stat ) are predicted when using ν μ CCQE interactions as a constraint. We use a simplified model to translate the MiniBooNE LEE observation into a prediction for a ν e signal in MicroBooNE. A Δ χ 2 test statistic, based on the combined Neyman–Pearson χ 2 formalism, is used to define frequentist confidence intervals for the LEE signal strength. Using this technique, in the case of no LEE signal, we expect this analysis to exclude a normalization factor of 0.75 (0.98) times the median MiniBooNE LEE signal strength at 90% ( 2 σ ) confidence level, while the MicroBooNE data yield an exclusion of 0.25 (0.38) times the median MiniBooNE LEE signal strength at 90% ( 2 σ ) confidence level.