Neutrino Oscillation Analysis Research Articles

Exploring atmospheric neutrino oscillations at ESSnuSB

This study provides an analysis of atmospheric neutrino oscillations at the ESSnuSB far detector facility. The prospects of the two cylindrical Water Cherenkov detectors with a total fiducial mass of 540 kt are investigated over 10 years of data taking in the standard three-flavor oscillation scenario. We present the confidence intervals for the determination of mass ordering, θ23 octant as well as for the precisions on sin2θ23 and Δm312\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\left|\\Delta {m}_{31}^2\\right| $$\\end{document}. It is shown that mass ordering can be resolved by 3σ CL (5σ CL) after 4 years (10 years) regardless of the true neutrino mass ordering. Correspondingly, the wrong θ23 octant could be excluded by 3σ CL after 4 years (8 years) in the case where the true neutrino mass ordering is normal ordering (inverted ordering). The results presented in this work are complementary to the accelerator neutrino program in the ESSnuSB project.

Importance sampling method for Feldman-Cousins confidence intervals

In various high-energy physics contexts, such as neutrino-oscillation experiments, several assumptions underlying the typical asymptotic confidence interval construction are violated, such that one has to resort to computationally expensive methods like the Feldman-Cousins method for obtaining confidence intervals with proper statistical coverage. By construction, the computation of intervals at high confidence levels requires fitting millions or billions of pseudoexperiments, while wasting most of the computational cost on overly precise intervals at low confidence levels. In this work, a simple importance sampling method is introduced that reuses pseudoexperiments produced for all tested parameter values in a single mixture distribution. This results in a significant error reduction on the estimated critical values, especially at high confidence levels, and simultaneously yields a correct interpolation of these critical values between the parameter values at which the pseudoexperiments were produced. The theoretically calculated performance is demonstrated numerically using a simple example from the analysis of neutrino oscillations. The relationship to similar techniques applied in statistical mechanics and p-value computations is discussed. Published by the American Physical Society 2024

Solar neutrino measurements using the full data period of Super-Kamiokande-IV

An analysis of solar neutrino data from the fourth phase of Super-Kamiokande (SK-IV) from October 2008 to May 2018 is performed and the results are presented. The observation time of the dataset of SK-IV corresponds to 2970 days and the total live time for all four phases is 5805 days. For more precise solar neutrino measurements, several improvements are applied in this analysis: lowering the data acquisition threshold in May 2015, further reduction of the spallation background using neutron clustering events, precise energy reconstruction considering the time variation of the PMT gain. The observed number of solar neutrino events in 3.49–19.49 MeV electron kinetic energy region during SK-IV is 65,443−388+390(stat.)±925(syst.) events. Corresponding B8 solar neutrino flux is (2.314±0.014(stat.)±0.040(syst.))×106 cm−2 s−1, assuming a pure electron-neutrino flavor component without neutrino oscillations. The flux combined with all SK phases up to SK-IV is (2.336±0.011(stat.)±0.043(syst.))×106 cm−2 s−1. Based on the neutrino oscillation analysis from all solar experiments, including the SK 5805 days dataset, the best-fit neutrino oscillation parameters are sin2θ12,solar=0.306±0.013 and Δm21,solar2=(6.10−0.81+0.95)×10−5 eV2, with a deviation of about 1.5σ from the Δm212 parameter obtained by KamLAND. The best-fit neutrino oscillation parameters obtained from all solar experiments and KamLAND are sin2θ12,global=0.307±0.012 and Δm21,global2=(7.50−0.18+0.19)×10−5 eV2. Published by the American Physical Society 2024

Atmospheric neutrino oscillation analysis with neutron tagging and an expanded fiducial volume in Super-Kamiokande I–V

We present a measurement of neutrino oscillation parameters with the Super-Kamiokande detector using atmospheric neutrinos from the complete pure-water SK I–V (April 1996–July 2020) dataset, including events from an expanded fiducial volume. The dataset corresponds to 6511.3 live days and an exposure of 484.2 kiloton-years. Measurements of the neutrino oscillation parameters Δm322, sin2θ23, sin2θ13, δCP, and the preference for the neutrino mass ordering are presented with atmospheric neutrino data alone, and with constraints on sin2θ13 from reactor neutrino experiments. Our analysis including constraints on sin2θ13 favors the normal mass ordering at the 92.3% level. Published by the American Physical Society 2024

Parametrized uncertainties in the spectral function model of neutrino charged-current quasielastic interactions for oscillation analyses

A substantial fraction of systematic uncertainties in neutrino oscillation experiments stem from the lack of precision in modeling the nuclear target in neutrino-nucleus interactions. Whilst this has driven significant progress in the development of improved nuclear models for neutrino scattering, it is crucial that the models used in neutrino data analyses be accompanied by parameters and associated uncertainties that allow the coverage of plausible nuclear physics. Based on constraints from electron scattering data, we propose such a set of parameters, which can be applied to nuclear shell models, and test their application to the Benhar [] spectral function model. The parametrization is validated through a series of maximum likelihood fits to cross section measurements made by the T2K and MINERvA experiments, which also permit an exploration of the power of near-detector data to provide constraints on the parameters in neutrino oscillation analyses. Published by the American Physical Society 2024

Neutrino oscillations in the Non-Kerr black hole with quantum phenomenon

Abstract In this paper, we have investigated the mathematical components of the Dirac equation in curved space-time and how it can be applied to the analysis of neutrino oscillations. More specifically, we have developed a method for calculating the phase shift in flavor neutrino oscillations by utilizing a Taylor series expansion of the action, taking into account $\Delta m^4$ orders. In addition, we have used this method to assess how the phase difference in neutrino mass eigenstates changes due to the gravitational field described by the Johannsen spacetime.

First attempt of directionality reconstruction for atmospheric neutrinos in a large homogeneous liquid scintillator detector

The directionality information of incoming neutrinos is essential to atmospheric neutrino oscillation analysis since it is directly related to the oscillation baseline length. Large homogeneous liquid scintillator detectors, while offering excellent energy resolution, are traditionally very limited in their capabilities of measuring event directionality. In this paper, we present a novel directionality reconstruction method for atmospheric neutrino events in large homogeneous liquid scintillator detectors based on waveform analysis and machine learning techniques. We demonstrate for the first time that such detectors can achieve good direction resolution and potentially play an important role in future atmospheric neutrino oscillation measurements. Published by the American Physical Society 2024

Neutrino oscillations as a single Feynman diagram

We propose an approach to neutrino oscillations in vacuum, based on quantum field theory (QFT). The neutrino emission and detection are identified with the charged-current vertices of a single second-order Feynman diagram for the underlying process, enclosing neutrino propagation between these two points. The key point of the presented approach is the definition of the space-time setup typical for neutrino oscillation experiments, implying macroscopically large but finite volumes of the source and detector separated by a sufficiently large distance L. We derive an L-dependent master formula for the charged lepton production rate, which provides the QFT basis for the analysis of neutrino oscillations. This formula depends on the underlying process and is not reducible to the conventional approach resorting to the concept of neutrino oscillation probability, which originates from non-relativistic quantum mechanics. We demonstrate that for some particular choice of the underlying process the derived master formula approximately coincides with the conventional one under some assumptions. In support to presented approach we show that it provides the QFT framework not only for neutrino–neutrino but also neutrino-antineutrino oscillations. It is also argued that the proposed formalism allows us to consistently incorporate medium effects, when neutrinos oscillate in dense matter.

An Algorithm to Obtain the Probability Oscillation of the Neutrino from the Atmosphere with a Layer Model of the Earth

The neutrino oscillation probability behavior traveling from the source in the atmosphere, its propagation through the Earth and its detection are shown using Earth Layers model by atmospheric neutrino oscillation analysis. Neutrino oscillation plots are generated from a developed computacional code, considering the influence or not of the atmosphere.

Impact of nuclear effects in energy reconstruction methods on sensitivity of neutrino oscillation parameters at NOνA experiment

Long baseline (LBL) neutrino experiments aim to measure the neutrino oscillation parameters to high precision. These experiments use nuclear targets for neutrino scattering and hence are inflicted with complexities of nuclear effects. Nuclear effects and their percolation into sensitivity measurement of neutrino oscillations parameters are not yet fully understood and therefore need to be dealt with carefully. In a recent work [1], we reported some results on this for NOνA experiment using the kinematic method of neutrino energy reconstruction, where it was observed that the nuclear effects are important in sensitivity analysis, and inclusion of realistic detector set up specifications increases uncertainty in this analysis as compared to ideal detector case. Precise reconstruction of neutrino energy is an important component in the extraction of oscillation parameters, and it is required that the neutrino energy is reconstructed with very high precision. With this motivation, in this work, we use two methods of neutrino energy reconstruction - kinematic and calorimetric, including the nuclear effects, and study their impact on sensitivity analysis. We consider nuclear interactions such as RPA and 2p2h and compare two energy reconstruction methods with reference to events generation, measurement of neutrino oscillation parameters Δm322 and θ23 for (νμ→νμ) disappearance channel, mass hierarchy sensitivity, and CP-violation sensitivity for (νμ→νe) appearance channel of the NOνA experiment. It is observed that with an ideal detector setup, the kinematic method shows significant dependence on nuclear effects, as compared to the calorimetric method. We also investigate the impact of realistic detector setup for NOνA in these two methods (with nuclear effects) and find that the calorimetric method shows more bias (uncertainty increases) in sensitivity contours, as compared to the kinematic method. This is found to be true for both the mass hierarchies and for both neutrino and antineutrino incoming beams. The results of this study can offer useful insights into future neutrino oscillation analysis at LBL experiments (including leptonic CP phase measurement), especially when we are in the precision measurement era for the same, particularly in the context of some nuclear effects and energy reconstruction methods.

Calorimetry in a Neutrino Observatory: The JUNO Experiment

The Jiangmen Underground Neutrino Observatory (JUNO) is a multipurpose experiment under construction in southern China; detector completion is expected in 2023. JUNO is a homogeneous calorimeter consisting of a target mass of 20 kt of an organic liquid scintillator, aiming to detect antineutrinos from reactors to investigate the neutrino oscillation mechanism. The scintillation and Cerenkov light emitted after the interaction of antineutrinos with the liquid scintillator is seen by a compound system of 20 inch large PMTs and 3 inch small PMTs, with a total photo-coverage of 78%. A dual-calorimetry technique is developed based on the presence of the two independent photosensor systems which are characterized by different average light level regimes, resulting in different dynamic ranges. Thanks to this novel technique, an unprecedented high light yield, and in combination with a comprehensive multiple-source and multi-position calibration campaign, JUNO is expected to reach energy-related systematic uncertainties below 1% and an effective energy resolution of 3% at 1%, required for the neutrino oscillation analysis.

Tau longitudinal and transverse polarizations from visible kinematics in (anti-)neutrino nucleus scattering

Since the ντ(ν¯τ)AZ→τ∓X reaction is notoriously difficult to be directly measured, the information on the dynamics of this nuclear process should be extracted from the analysis of the energy and angular distributions of the tau decay visible products. These distributions depend, in addition to d2σ/(dEτdcos⁡θτ), on the components of the tau-polarization vector. We give, for the first time, the general expression for the outgoing hadron (pion or rho meson) energy and angular differential cross section for the sequential ντAZ→τ−(π−ντ,ρ−ντ)X and ν¯τAZ→τ+(π+ν¯τ,ρ+ν¯τ)X reactions. Though all possible nuclear reaction mechanisms contribute to the distribution, it may be possible to isolate/enhance one of them by implementing appropriate selection criteria. For the case of the quasi-elastic reaction off oxygen and neutrino energies below 6 GeV, we show that the pion distributions are quite sensitive to the details of the tau-polarization components. We find significant differences between the full calculation, where the longitudinal and transverse components of the tau polarization vector vary with the energy and the scattering angle of the produced tau, and the simplified scheme in which the polarizations are set to one and zero, being the latter their respective asymptotic values reached in the high energy regime. In addition to its potential impact on neutrino oscillation analyses, this result can be used to further test different nuclear models, since these observables provide complementary information to that obtained by means of the inclusive nuclear weak charged-current differential cross section. We also study the effects on the cross section of the W4 and W5 nuclear structure functions, which contributions are proportional to the charged lepton mass, and therefore difficult to constrain in muon and electron neutrino experiments.

Low energy event classification in IceCube using boosted decision trees

The DeepCore sub-array within the IceCube Neutrino Observatory is a densely instrumented region of Antarctic ice designed to observe atmospheric neutrino interactions above 5 GeV via Cherenkov radiation. An essential aspect of any neutrino oscillation analysis is the ability to accurately identify the flavor of neutrino events in the detector. This task is particularly difficult at low energies when very little light is deposited in the detector. Here we discuss the use of machine learning to perform event classification at low energies in IceCube using a boosted decision tree (BDT). A BDT is trained using reconstructed quantities to identify track-like events, which result from muon neutrino charged current interactions. This new method improves the accuracy of particle identification compared to traditional classification methods which rely on univariate straight cuts.

Neutrino Oscillations in Neutrino-Dominated Accretion Around Rotating Black Holes

In the binary-driven hypernova model of long gamma-ray bursts, a carbon–oxygen star explodes as a supernova in the presence of a neutron star binary companion in close orbit. Hypercritical (i.e., highly super-Eddington) accretion of the ejecta matter onto the neutron star sets in, making it reach the critical mass with consequent formation of a Kerr black hole. We have recently shown that, during the accretion process onto the neutron star, fast neutrino flavor oscillations occur. Numerical simulations of the above system show that a part of the ejecta stays bound to the newborn Kerr black hole, leading to a new process of hypercritical accretion. We address herein, also for this phase of the binary-driven hypernova, the occurrence of neutrino flavor oscillations given the extreme conditions of high density (up to 1012 g cm−3) and temperatures (up to tens of MeV) inside this disk. We estimate the behavior of the electronic and non-electronic neutrino content within the two-flavor formalism (νeνx) under the action of neutrino collective effects by neutrino self-interactions. We find that in the case of inverted mass hierarchy, neutrino oscillations inside the disk have frequencies between ∼(105–109) s−1, leading the disk to achieve flavor equipartition. This implies that the energy deposition rate by neutrino annihilation (ν+ν¯→e−+e+) in the vicinity of the Kerr black hole is smaller than previous estimates in the literature not accounting for flavor oscillations inside the disk. The exact value of the reduction factor depends on the νe and νx optical depths but it can be as high as ∼5. The results of this work are a first step toward the analysis of neutrino oscillations in a novel astrophysical context, and as such, deserve further attention.

Grid-based minimization at scale: Feldman-Cousins corrections for light sterile neutrino search

High Energy Physics (HEP) experiments generally employ sophisticated statistical methods to present results in searches of new physics. In the problem of searching for sterile neutrinos, likelihood ratio tests are applied to short-baseline neutrino oscillation experiments to construct confidence intervals for the parameters of interest. The test statistics of the form Δχ2 is often used to form the confidence intervals, however, this approach can lead to statistical inaccuracies due to the small signal rate in the region-of-interest. In this paper, we present a computational model for the computationally expensive Feldman-Cousins corrections to construct a statistically accurate confidence interval for neutrino oscillation analysis. The program performs a grid-based minimization over oscillation parameters and is written in C++. Our algorithms make use of vectorization through Eigen3, yielding a single-core speed-up of 350 compared to the original implementation, and achieve MPI data parallelism by employing DIY. We demonstrate the strong scaling of the application at High-Performance Computing (HPC) sites. We utilize HDF5 along with HighFive to write the results of the calculation to file.

The fate of hints: updated global analysis of three-flavor neutrino oscillations

Our herein described combined analysis of the latest neutrino oscillation data presented at the Neutrino2020 conference shows that previous hints for the neutrino mass ordering have significantly decreased, and normal ordering (NO) is favored only at the 1.6σ level. Combined with the χ2 map provided by Super-Kamiokande for their atmospheric neutrino data analysis the hint for NO is at 2.7σ. The CP conserving value δCP = 180° is within 0.6σ of the global best fit point. Only if we restrict to inverted mass ordering, CP violation is favored at the ∼ 3σ level. We discuss the origin of these results — which are driven by the new data from the T2K and NOvA long-baseline experiments —, and the relevance of the LBL-reactor oscillation frequency complementarity. The previous 2.2σ tension in ∆m221 preferred by KamLAND and solar experiments is also reduced to the 1.1σ level after the inclusion of the latest Super-Kamiokande solar neutrino results. Finally we present updated allowed ranges for the oscillation parameters and for the leptonic Jarlskog determinant from the global analysis.

Neutrino Oscillation Analysis of 217 Live Days of Daya Bay and 500 Live Days of RENO

We present a neutrino oscillation analysis of two particular data sets from the Daya Bay and RENO reactor neutrino experiments aiming to study the increase in precision in the oscillation parameters sin22θ13 and the effective mass splitting Δmee2 gained by combining two relatively simple to reproduce analyses available in the literature. For Daya Bay, the data from 217 days between December 2011 and July 2012 were used. For RENO, we used the data from 500 live days between August 2011 and January 2012. We reproduce reasonably well the results of the individual analyses, both rate-only and spectral, defining a suitable χ2 statistic for each case. Finally, we performed a combined spectral analysis and extract tighter constraints on the parameters, with an improved precision between 30 and 40% with respect to the individual analyses considered.

Three-flavor neutrino oscillations and beyond

In this work we summarize the current status of global neutrino oscillation analyses in the three-neutrino framework. We first describe the different data samples included in the global fit, emphasizing the role of each of them in constraining a given set of parameters. Next, we discuss the main improvements obtained thanks to the consideration of the latest experimental data. The status of the yet-unknown parameters, such as the true neutrino mass ordering, the Dirac CP-violating phase and the octant of the atmospheric mixing angle is also commented. Finally, we discuss some scenarios where the measurement of the reactor mixing angle or the CP violation phase could be significantly affected by the presence of neutrino physics beyond the Standard Model.

Electron versus Muon Neutrino Induced Cross Sections in Charged Current Quasielastic Processes.

Differences between ν_{e} and ν_{μ} quasielastic cross sections are essential in neutrino oscillation analyses and CP violation searches for experiments such as DUNE and T2HK. The ratio of these is however poorly known experimentally and for certain kinematic regions theoretical models give contradictory answers. We use two independent mean-field based models to investigate this ratio using ^{40}Ar and ^{12}C targets. We demonstrate that a proper treatment of the final nucleon's wave function confirms the dominance of ν_{μ} over ν_{e} induced cross sections at forward lepton scattering.

Linear analysis of fast-pairwise collective neutrino oscillations in core-collapse supernovae based on the results of Boltzmann simulations

Neutrinos are densely populated deep inside the core of massive stars after their gravitational collapse to produce supernova explosions and form compact stars such as neutron stars (NS) and black holes (BH). It has been considered that they may change their flavor identities through so-called fast-pairwise conversions induced by mutual forward scatterings. If that is really the case, the dynamics of supernova explosion will be influenced, since the conversion may occur near the neutrino sphere, from which neutrinos are effectively emitted. In this paper, we conduct a pilot study of such possibilities based on the results of fully self-consistent, realistic simulations of a core-collapse supernova explosion in two spatial dimensions under axisymmetry. As we solved the Boltzmann equations for neutrino transfer in the simulation not as a post-process but in real time, the angular distributions of neutrinos in momentum space for all points in the core at all times are available, a distinct feature of our simulations. We employ some of these distributions extracted at a few selected points and times from the numerical data and apply linear analysis to assess the possibility of the conversion. We focus on the vicinity of the neutrino sphere, where different species of neutrinos move in different directions and have different angular distributions as a result. This is a pilot study for a more thorough survey that will follow soon. We find no positive sign of conversion unfortunately at least for the spatial points and times we studied in this particular model. We hence investigate rather in detail the condition for the conversion by modifying the neutrino distributions rather arbitrarily by hand.