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At least 145 records · Page 8

Inclusive Search for Anomalous Single-Photon Production in MicroBooNE

We present an inclusive search for anomalous production of single-photon events from neutrino interactions in the MicroBooNE experiment. The search and its signal definition are motivated by the previous observation of a low-energy excess of electromagnetic shower events from the MiniBooNE experiment. We use the Wire-Cell reconstruction framework to select a sample of inclusive single-photon final-state interactions with a final efficiency and purity of 7.0% and 40.2%, respectively. We leverage simultaneous measurements of sidebands of charged current 𝜈 𝜇 interactions and neutral current interactions producing 𝜋 0 mesons to constrain signal and background predictions and reduce uncertainties. We perform a blind analysis using a dataset collected from February 2016 to July 2018, corresponding to an exposure of 6.34 × 10 20 protons on target from the Booster Neutrino Beam at Fermilab. In the full signal region, we observe agreement between the data and the prediction, with a goodness-of-fit 𝑝 value of 0.11. We then isolate a subsample of these events containing no visible protons, and observe 93 ± 22⁢(stat) ±35⁢(syst) data events above prediction, corresponding to just above 2⁢𝜎 local significance, concentrated at shower energies below 600 MeV.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

Relativistic effects in Green's function Monte Carlo calculations of neutrino-nucleus scattering

Here, microscopic calculations of neutrino-nucleus scattering cross sections are critical for the success of the neutrino-oscillation program. In addition to retaining nuclear correlations in the initial and final state of the reaction, they are based on consistent nuclear interactions and transition current operators, thereby enabling robust uncertainty quantification. In this work, we address a significant limitation of these microscopic methods, which arises from their nonrelativistic nature. By performing the calculations in a reference frame that minimizes nucleon momenta and utilizing the so-called two-fragment model, we extend the applicability of Green's function Monte Carlo calculations of neutrino-nucleus scattering to higher momenta than currently possible. To validate this approach, we compare our theoretical predictions against inclusive data measured by the MiniBooNE, T2K, and MINER ν A experiments.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

Realistic spectral function model for charged-current quasielastic-like neutrino and antineutrino scattering cross sections on C 12

A detailed study of charged current quasielastic neutrino and antineutrino scattering cross sections on a 12 C target with no pions in the final state is presented. The initial nucleus is described by means of a realistic spectral function S($p$,E) in which nucleon-nucleon correlations are implemented by using natural orbitals through the Jastrow method. The roles played by these correlations and by final-state interactions are analyzed and discussed. The model also includes the contribution of weak two-body currents in the two-particle two-hole sector, evaluated within a fully relativistic Fermi gas. The theoretical predictions are compared with a large set of experimental data for double-differential, single-differential, and total integrated cross sections measured by the MiniBooNE, MINER ν A , and T2K experiments. Good agreement with experimental data is found over the whole range of neutrino energies. The results are also in global good agreement with the predictions of the superscaling approach, which is based on the analysis of electron-nucleus scattering data, with only a few differences seen at specific kinematics.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

Decaying sterile neutrinos and the short baseline oscillation anomalies

The MiniBooNE experiment has observed a significant excess of electron neutrinos in a muon neutrino beam, in conflict with standard neutrino oscillations. We discuss the possibility that this excess is explained by a sterile neutrino with a mass ~1 keV that decays quickly back into active neutrinos plus a new light boson. This scenario satisfies terrestrial and cosmological constraints because it has neutrino self-interactions built-in. Accommodating also the LSND, reactor, and gallium anomalies is possible, but requires an extension of the model to avoid cosmological limits.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

Neutrino-nucleus CC 0 π cross-section tuning in GENIE v3

This article summarizes the state of the art of v μ and $\bar{v}_μ$ CC0π cross-section measurements on carbon and argon and discusses the relevant nuclear models, parametrizations and uncertainties in GENIE v3. The CC0π event topology is common in experiments at a few-GeV energy range. Although its main contribution comes from quasi-elastic interactions, this topology is still not well understood. The GENIE global analysis framework is exploited to analyze CC0π datasets from MiniBooNE, T2K and MINERvA. A partial tune for each experiment is performed, providing a common base for the discussion of tensions between datasets. The results offer an improved description of nuclear CC0π datasets as well as data-driven uncertainties for each experiment. This work is a step towards a GENIE global tune that improves our understanding of neutrino interactions on nuclei. It follows from earlier GENIE work on the analysis of neutrino scattering datasets on hydrogen and deuterium.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

Global fit of electron and neutrino elastic scattering data to determine the strange quark contribution to the vector and axial form factors of the nucleon

We present a global fit of neutral-current elastic (NCE) neutrino-scattering data and parity-violating electron-scattering (PVES) data with the goal of determining the strange quark contribution to the vector and axial form factors of the proton. Previous fits of this form included data from a variety of PVES experiments (PVA4, HAPPEx, G0, SAMPLE) and the NCE neutrino and anti-neutrino data from BNL E734. These fits did not constrain the strangeness contribution to the axial form factor G A s ( Q 2 ) at low Q 2 very well because there was no NCE data for Q 2 < 0.45 GeV 2 . Our new fit includes for the first time MiniBooNE NCE data from both neutrino and antineutrino scattering; this experiment used a hydrocarbon target and so a model of the neutrino interaction with the carbon nucleus was required. Three different nuclear models have been employed: a relativistic Fermi gas model, the superscaling approximation model, and a spectral function model. We find a tremendous improvement in the constraint of G A s ( Q 2 ) at low Q 2 compared to previous work, although more data is needed from NCE measurements that focus on exclusive single-proton final states, for example from MicroBooNE. Published by the American Physical Society 2024

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

New μ forces from ν μ sources

Accelerator-based experiments reliant on charged pion and kaon decays to produce muon-neutrino beams also deliver an associated powerful flux of muons. Therefore, these experiments can additionally be sensitive to light new particles that preferentially couple to muons and decay to visible final states on macroscopic length scales. Such particles are produced through rare 3-body meson decays in the decay pipe or via muon scattering in the beam dump, and decay in a downstream detector. To demonstrate the potential of this search strategy, we recast existing MiniBooNE and MicroBooNE studies of neutral pion production in neutrino-induced neutral-current scattering ( ν μ N → ν μ N π 0 , π 0 → γ γ ) to place limits on light ( < 2 m μ ) muon-philic scalar particles that decay to diphotons through loops of virtual muons. While much of this parameter space has already been excluded by E137, we also project that SBND can be sensitive to unexplored parameter space for these models, and provide a road map for future neutrino experiments to perform dedicated searches for muon-philic forces. Published by the American Physical Society 2024

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

Testing light dark matter coannihilation with fixed-target experiments

In this paper, we introduce a novel program of fixed-target searches for thermal-origin Dark Matter (DM), which couples inelastically to the Standard Model. Since the DM only interacts by transitioning to a heavier state, freeze-out proceeds via coannihilation and the unstable heavier state is depleted at later times. For sufficiently large mass splittings, direct detection is kinematically forbidden and indirect detection is impossible, so this scenario can only be tested with accelerators. Here we propose new searches at proton and electron beam fixed-target experiments to probe sub-GeV coannihilation, exploiting the distinctive signals of up- and down-scattering as well as decay of the excited state inside the detector volume. We focus on a representative model in which DM is a pseudo-Dirac fermion coupled to a hidden gauge field (dark photon), which kinetically mixes with the visible photon. We define theoretical targets in this framework and determine the existing bounds by reanalyzing results from previous experiments. We find that LSND, E137, and BaBar data already place strong constraints on the parameter space consistent with a thermal freeze-out origin, and that future searches at Belle II and MiniBooNE, as well as recently-proposed fixed-target experiments such as LDMX and BDX, can cover nearly all remaining gaps. We also briefly comment on the discovery potential for proposed beam dump and neutrino experiments which operate at much higher beam energies.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

Neutrinos in large extra dimensions and short-baseline ν e appearance

Here, we show that, in the presence of bulk masses, sterile neutrinos propagating in large extra dimensions (LED) can induce electron-neutrino appearance effects. This is in contrast to what happens in the standard LED scenario, and hence LED models with explicit bulk masses have the potential to address the MiniBooNE and LSND appearance results as well as the reactor and Gallium anomalies. A special feature in our scenario is that the mixing of the first Kaluza-Klein modes to active neutrinos can be suppressed, making the contribution of heavier sterile neutrinos to oscillations relatively more important. We study the implications of this neutrino mass generation mechanism for current and future neutrino oscillation experiments and show that the Short Baseline Neutrino Program at Fermilab will be able to efficiently probe such a scenario. In addition, this framework leads to massive Dirac neutrinos and thus precludes any signal in neutrinoless double beta decay experiments.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

Axial-vector form factors of the nucleon from lattice QCD

In this paper, we present results for the form factors of the isovector axial vector current in the nucleon state using large scale simulations of lattice QCD. The calculations were done using eight ensembles of gauge configurations generated by the MILC collaboration using the HISQ action with 2 + 1 + 1 dynamical flavors. These ensembles span three lattice spacings a ≈ 0.06 , 0.09, and 0.12 fm and light-quark masses corresponding to the pion masses M π ≈ 135, 225, and 310 MeV. High-statistics estimates allow us to quantify systematic uncertainties in the extraction of G A (Q 2 ) and the induced pseudoscalar form factor G P (Q 2 ) . We perform a simultaneous extrapolation in the lattice spacing, lattice volume and light-quark masses of the axial charge radius r A data to obtain physical estimates. Using the dipole ansatz to fit the Q 2 behavior we obtain r A | dipole = 0.49(3) fm , which corresponds to M A = 1.39(9) GeV , and is consistent with M A = 1.35(17) GeV obtained by the miniBooNE collaboration. The estimate obtained using the z -expansion is r A | z - expansion = 0.46(6) fm, and the combined result is r A | combined = 0.48(4) fm. Analysis of the induced pseudoscalar form factor G P (Q 2 ) yields low estimates for g* P and g π NN compared to their phenomenological values. To understand these, we analyze the partially conserved axial current (PCAC) relation by also calculating the pseudoscalar form factor. Lastly, we find that these low values are due to large deviations in the PCAC relation between the three form factors, and in the pion-pole dominance hypothesis.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

Neutral weak-current two-body contributions in inclusive scattering from {sup 12}C

An {\it ab initio} calculation of the sum rules of the neutral weak response functions in $^{12}$C is reported, based on a realistic Hamiltonian, including two- and three-nucleon potentials, and on realistic currents, consisting of one- and two-body terms. We find that the sum rules of the response functions associated with the longitudinal and transverse components of the (space-like) neutral current are largest and that a significant portion ($\simeq 30$\%) of the calculated strength is due to two-body terms. This fact may have implications for the MiniBooNE and other neutrino quasi-elastic scattering data on nuclei.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗

Enhanced active-sterile neutrino polarizability at the intensity frontier

Electromagnetic probes of neutrinos can provide insights into physics beyond the Standard Model. Among the possible electromagnetic interactions of neutrinos is neutrino polarizability, a dimension-7 effective operator that couples two neutrinos to two photons. In this manuscript, we study a realization of the neutrino polarizability operator in which one of the active neutrinos is replaced by a sterile neutrino. We derive new constraints on this active-sterile neutrino polarizability from its contribution to neutrino-nucleus scattering with a single photon in the final state at neutrino experiments. We show that a realization of this operator via a light mediator can explain the MiniBooNE low-energy excess while remaining consistent with other experimental constraints. Finally, we comment on additional model realizations of this higher-dimensional operator.

Neutrinos↗

Monophotons at neutrino experiments from neutrino polarizability

Nontrivial electromagnetic properties of neutrinos are an avenue to physics beyond the Standard Model (SM). To this end, we investigate the power of monophoton signals at neutrino experiments to probe a higher-dimensional operator connecting neutrinos to SM photons dubbed, neutrino polarizability. A simplified scenario giving rise to this operator involves a new pseudoscalar that couples to both neutrinos and photons, with clear implications for axionlike particle (ALP) and Majoron physics. By analyzing the photon energy spectrum and angular distributions, we find that NOMAD and MiniBooNE currently set the most stringent limits, while short baseline near detector and the DUNE near detector will soon provide significantly improved constraints.

Particle detection signatures↗

Muon-neutrino disappearance with multiple liquid argon time projection chambers in the Fermilab Booster neutrino beam

The Short Baseline Neutrino (SBN) program consists of three liquid argon time projection chamber (LArTPC) experiments: SBND, MicroBooNE and ICARUS, with 110 m, 470 m and 600 m baselines respectively. The detectors are located in the Booster Neutrino Beam (BNB) at Fermilab which has a peak energy around 0.7 GeV and contains predominantly muon neutrinos. The baseline and energy range of the SBN program is conducive to measuring neutrino oscillation parameters under various sterile neutrino hypotheses. Sterile neutrinos have been proposed as a possible solution to the numerous short baseline anomalies. The proposed particles must be sterile in nature such that they do not interact via the weak force, however they may undergo oscillations with the active neutrino flavours. Their existence may consequently be confirmed through measurements of the appearance and disappearance of the active flavours. The analyses presented in this thesis aimed to calculate and understand the sensitivity of the SBN program to measuring the ?µ disappearance parameters under the (3+1) sterile neutrino oscillation hypothesis. The sensitivity of SBN to measuring the ?µ disappearance sterile oscillation parameters, sin2 2?µµ, ?m2 41, was calculated through semi-exclusive joint fits of the ?µ CC 0p and ?µ CC Other reconstructed neutrino energy spectra. The first iteration used truth-level Monte Carlo (MC) events, and determined that the 5s SBN sensitivity is comparable to the 90% MINOS/MINOS+ confidence level and supersedes the 90% MiniBooNE confidence level across entire phase space. Semi-exclusive joint fits of the aforementioned sample spectra were performed between the MC and multiple mock data sets in SBND. This analysis assessed the accuracy with which the near detector can disentangle systematic from physics effects in the oscillation analysis. The result was a 5.49% discrepancy between the ICARUS Monte Carlo and mock data event rates, when the systematic constraints from the near detector fit were extrapolated to the far detector. The second iteration of the SBN sensitivity analysis involved the application of an event selection procedure developed in SBND, following the full reconstruction chain. ?µ CC 0p events were selected from sample of neutrinos with 84.5% efficiency and 84.3% purity. The sterile neutrino sensitivity was determined once more at the near detector with these samples, and was shown to be consistent with the truth-level studies.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗

Identifying Muon Neutrino Charged-Current Interactions in the MicroBooNE Detector

The MicroBooNE experiment is a short-baseline neutrino experiment at the Fermi National Accelerator Laboratory (FNAL) in the US, receiving a highly pure muon neutrino beam from the Booster Neutrino Beam (BNB) and taking data since October 2015. The main physics goal of MicroBooNE is to clarify the nature of the low-energy excess of electron-like events observed by the MiniBooNE Cherenkov detector, which due to its detector technology is unable to resolve whether the observed excess shower-like events are due to electrons or photons. Instead, MicrooBooNE employs cutting-edge liquid argon time projection chamber (LArTPC) technology, which offers excellent spatial and calorimetric resolution, which makes it possible to reconstruct complex neutrino interactions and to efficiently distinguish different final state particle types. This thesis presents a fully-automated event selection of interactions of the types ν μ +Ar → μ - + X and ν μ + Ar → μ - + p + X developed using the Pandora multi-algorithm approach to pattern recognition for LArTPC experiments. The analysis in this work is performed on a subset of the MicroBooNE Run 1 dataset corresponding to 4.52 × 10 19 protons on target acquired by the MicroBooNE detector between February and October 2016. The analysis quantifies the main signal and background interaction channels that produce a reconstructed neutrino interaction with one and two particles in the final state, and quantifies the extent to which different aspects of the Pandora reconstruction affect the selection performance. MicroBooNE is a surface detector, and therefore cosmic-ray tracks are the main observed background. A direction fitting procedure has been implemented in this analysis to formulate directional probabilities, using the Bethe equation and the high-resolution calorimetric information of MicroBooNE, to reduce this cosmic-ray background. This functionality is used to enhance the efficiency of the Pandora cosmic ray tagging logic, and the impact of this procedure on the reconstruction and event selection performance is analysed. The result of this study is two fully-automated selections of ν μ +Ar → μ - + X (57.91% pure) and ν μ + Ar → μ - + p + X (78.30% pure) with efficiencies of 64.35% and 62.65%, respectively.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗

Using L/E Oscillation Probability Distributions

This paper explores the use of L /E oscillation probability distributions to compare experimental measurements and to evaluate oscillation models. In this case, L is the distance of neutrino travel and E is a measure of the interacting neutrino’s energy. While comparisons using allowed and excluded regions for oscillation model parameters are likely the only rigorous method for these comparisons, the L /E distributions are shown to give qualitative information on the agreement of an experiment’s data with a simple two-neutrino oscillation model. In more detail, this paper also outlines how the L /E distributions can be best calculated and used for model comparisons. Specifically, the paper presents the L /E data points for the final MiniBooNE data samples and, in the Appendix, explains and corrects the mistaken analysis published by the ICARUS collaboration.

Aguilar-Arevalo, A. A.↗

LAr1-ND: Testing Neutrino Anomalies with Multiple LAr TPC Detectors at Fermilab

This Proposal seeks to continue the development of the short-baseline neutrino oscillation program at Fermilab with the construction of the Liquid Argon Near Detector, or LArl-ND, to be located in an existing experimental enclosure 100 m from the Booster Neutrino Beam target. The physics program will contribute, in conjunction with MicroBooNE, to the in terpretation of the MiniBooNE neutrino-mode anomaly and will enable additional tests of high-$\Delta m^2$ neutrino oscillations through both disappearance and appearance searches. Leveraging the advanced design work performed for LBNE and the very recent experience of the MicroBooNE detector construction, the LArl-ND project has the potential to move forward quickly. Due to the high event rate at the near location, significant physics output can be achieved with a relatively short run. Beyond this near-term program, LArl-ND could also serve as the near detector in a three LAr TPC experiment capable of definitively addressing the existing anomalies also in antineutrinos and making precision measurements of high-$\Delta m^2$ neutrino oscillations. In addition to the physics program, LArl-ND, following the MicroBooNE model, will have a development program serving as an engineering prototype for LAr TPCs for long baseline CP-violation searches in the future (e.g.: LBNE).

Admas, C.↗