Analysis Of Atmospheric Neutrino Data Research Articles

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.

Atmospheric neutrino oscillation analysis with improved event reconstruction in Super-Kamiokande IV

A new event reconstruction algorithm based on a maximum likelihood method has been developed for Super-Kamiokande. Its improved kinematic and particle identification capabilities enable the analysis of atmospheric neutrino data in a detector volume 32% larger than previous analyses and increases sensitivity to the neutrino mass hierarchy. Analysis of a 253.9 kton-year exposure of the Super-Kamiokande IV atmospheric neutrino data has yielded a weak preference for the normal hierarchy, disfavoring the inverted hierarchy at 74% assuming oscillations at the best fit of the analysis.

Global analysis of three-flavour neutrino oscillations: synergies and tensions in the determination of \u03b823, \u03b4CP, and the mass ordering

We present the results of a global analysis of the neutrino oscillation data available as of fall 2018 in the framework of three massive mixed neutrinos with the goal at determining the ranges of allowed values for the six relevant parameters. We describe the complementarity and quantify the tensions among the results of the different data samples contributing to the determination of each parameter. We also show how those vary when combining our global likelihood with the χ2 map provided by Super-Kamiokande for their atmospheric neutrino data analysis in the same framework. The best fit of the analysis is for the normal mass ordering with inverted ordering being disfavoured with a Δχ2 = 4.7 (9.3) without (with) SK-atm. We find a preference for the second octant of θ23, disfavouring the first octant with Δχ2 = 4.4 (6.0) without (with) SK-atm. The best fit for the complex phase is δCP = 215° with CP conservation being allowed at Δχ2 = 1.5 (1.8). As a byproduct we quantify the correlated ranges for the laboratory observables sensitive to the absolute neutrino mass scale in beta decay, {m}_{nu_e} , and neutrino-less double beta decay, mee, and the total mass of the neutrinos, Σ, which is most relevant in Cosmology.

Atmospheric neutrino oscillation analysis with external constraints in Super-Kamiokande I-IV

An analysis of atmospheric neutrino data from all four run periods of \superk optimized for sensitivity to the neutrino mass hierarchy is presented. Confidence intervals for $\Delta m^2_{32}$, $\sin^2 \theta_{23}$, $\sin^2 \theta_{13}$ and $\delta_{CP}$ are presented for normal neutrino mass hierarchy and inverted neutrino mass hierarchy hypotheses based on atmospheric neutrino data alone. Additional constraints from reactor data on $\theta_{13}$ and from published binned T2K data on muon neutrino disappearance and electron neutrino appearance are added to the atmospheric neutrino fit to give enhanced constraints on the above parameters. Over the range of parameters allowed at 90% confidence level, the normal mass hierarchy is favored by between 91.5% and 94.5% based on the combined result.

Global constraints on muon-neutrino nonstandard interactions

The search for new interactions of neutrinos beyond those of the Standard Model may help to elucidate the mechanism responsible for neutrino masses. Here we combine existing accelerator neutrino data with restrictions coming from a recent atmospheric neutrino data analysis in order to lift parameter degeneracies and improve limits on new interactions of muon neutrinos with quarks. In particular we re-consider the results of the NuTeV experiment in view of a new evaluation of its systematic uncertainties. We find that, although constraints for muon neutrinos are better than those applicable to tau or electron neutrinos, they lie at the few $\times 10^{-2}$ level, not as strong as previously believed. We briefly discuss prospects for further improvement.

Extraction of the atmospheric neutrino fluxes from experimental event rate data

Precise knowledge of the atmospheric neutrino fluxes is a key ingredient in the interpretation of the results from any atmospheric neutrino experiment. In the standard atmospheric neutrino data analysis, these fluxes are theoretical inputs obtained from sophisticated numerical calculations. In this contribution, we present an alternative approach to the determination of the atmospheric neutrino fluxes based on the direct extraction from the experimental data on neutrino event rates. The extraction is achieved by means of a combination of artificial neural networks as interpolants and Monte Carlo methods.

Determination of the atmospheric neutrino flux from experimental data

The precise knowledge of the atmospheric neutrino fluxes is a key ingredient in the interpretation of the results from any atmospheric neutrino experiment. In the standard atmospheric neutrino data analysis, these fluxes are theoretical inputs obtained from sophisticated numerical calculations. In this work we present an alternative approach to the determination of the atmospheric neutrino fluxes based on the direct extraction from the experimental data on neutrino event rates.

Determination of the atmospheric neutrino fluxes from atmospheric neutrino data

The precise knowledge of the atmospheric neutrino fluxes is a key ingredient in the interpretation of the results from any atmospheric neutrino experiment. In the standard atmospheric neutrino data analysis, these fluxes are theoretical inputs obtained from sophisticated numerical calculations based on the convolution of the primary cosmic ray spectrum with the expected yield of neutrinos per incident cosmic ray. In this work we present an alternative approach to the determination of the atmospheric neutrino fluxes based on the direct extraction from the experimental data on neutrino event rates. The extraction is achieved by means of a combination of artificial neural networks as interpolants and Monte Carlo methods for faithful error estimation

Measurement of the zenith angle distribution of the cosmic muon flux in Hanoi

The zenith angle distribution of the cosmic muon flux has been measured in Hanoi, where the geomagnetic rigidity cutoff reaches the very high value of 17 GV, using an orientable scintillator telescope. The measurement is of interest for the understanding of the development of cosmic ray showers in the earth atmosphere. The dependence of the cosmic muon flux (integrated over charges and momenta) on zenith angle θ is measured to be of the approximate form ( Φ 0− asin 2 θ)×cos 2 θ with Φ 0=72.0±1.6 m −2 sr −1 s −1 and a=7.8±0.8 m −2 sr −1 s −1 . This result is consistent with an earlier Hanoi measurement and is in excellent agreement with the prediction of a model widely used in the analysis of atmospheric neutrino data.

Updated analysis of atmospheric neutrino data

In the context of the latest (79.5 kTy) Super-Kamiokande atmospheric neutrino data, we present an updated analysis of the mass and mixing parameters relevant for two-, three-, and four-family neutrino mixing. Oscillations in the ν μ→ν τ channel clearly emerge as the dominant mechanism responsible for the atmospheric ν μ anomaly, with no significant indication for subdominant mixing with electron or sterile neutrinos. Upper bounds on subdominant mixing angles are also discussed.

Measurement of the vertical cosmic muon flux in a region of large rigidity cutoff

The vertical cosmic muon flux has been measured in Hanoi using a segmented scintillator hodoscope. It is the first measurement performed at VATLY, a cosmic ray laboratory recently created in Vietnam and installed in the premises of the Institute for Nuclear Sciences and Techniques. The measurement, performed at sea level in a region where the geomagnetic rigidity cutoff reaches 17 GV, is of interest for the understanding of the development of cosmic ray showers in the earth atmosphere. The result is compared with the prediction of a model widely used in the analysis of atmospheric neutrino data.

Neutrino Oscillations with Two Δm2 Scales

An approximation that is often used in fits to reactor and atmospheric neutrino data and in some studies of future neutrino oscillation experiments is to assume one dominant scale, $\Delta m^2$, of neutrino mass squared differences, in particular, $\Delta m^2_{atm} \sim 3 \times 10^{-3}$ eV$^2$. Here we investigate the corrections to this approximation arising from the quantity $\Delta m^2_{sol}$ relevant for solar neutrino oscillations, assuming the large mixing angle solution. We show that for values of $\sin^2(2\theta_{13}) \sim 10^{-2}$ (in the range of interest for long-baseline neutrino oscillation experiments with either intense conventional neutrino beams such as JHF-SuperK or a possible future neutrino factory) and for $\Delta m^2_{sol} \sim 10^{-4}$ eV$^2$, the contributions to $\nu_\mu \to\nu_e$ oscillations from both CP-conserving and CP-violating terms involving $\sin^2(\Delta m^2_{sol}L/(4E))$ can be comparable to the terms involving $\sin^2(\Delta m^2_{atm}L/(4E))$ retained in the one-$\Delta m^2$ approximation. Accordingly, we emphasize the importance of performing a full three-flavor, two-$\Delta m^2$ analysis of the data on $\nu_\mu \to \nu_e$ oscillations in a conventional-beam experiment and $\nu_e \to \nu_\mu$, $\bar\nu_e \to \bar\nu_\mu$ oscillations at a neutrino factory. We also discuss a generalized analysis method for the KamLAND reactor experiment, and note how the information from this experiment can be used to facilitate the analysis of the subsequent data on $\nu_\mu \to \nu_e$ oscillations. Finally, we consider the analysis of atmospheric neutrino data and present calculations of matter effects in a three-flavor, two-$\Delta m^2$ framework relevant to this data and to neutrino factory measurements.

Analysis of the atmospheric neutrino data in terms of 3ν oscillations

A global analysis of atmospheric and reactor neutrino data is presented in terms of three-neutrino oscillations. We consider in our analysis both contained events and upward-going ν-induced muon events, including the previous data samples of Fréjus, IMB, Nusex, and Kamioka experiments as well as the full 71 kton-yr (1144 days) Super-Kamiokande data set, the recent 5.1 kton-yr contained events of Soudan-2 and the results on upgoing muons from the MACRO detector. After presenting the results for the analysis of atmospheric data alone, we add to our data sample the reactor bound of the CHOOZ experiment, showing and important complementarity between the atmospheric and reactor limits which results in a stronger constraint on the allowed value of θ 13.

Evidence for Oscillation of Atmospheric Neutrinos

We present an analysis of atmospheric neutrino data from a 33.0 kton yr (535-day) exposure of the Super-Kamiokande detector. The data exhibit a zenith angle dependent deficit of muon neutrinos which is inconsistent with expectations based on calculations of the atmospheric neutrino flux. Experimental biases and uncertainties in the prediction of neutrino fluxes and cross sections are unable to explain our observation. The data are consistent, however, with two-flavor ${\ensuremath{\nu}}_{\ensuremath{\mu}}\ensuremath{\leftrightarrow}{\ensuremath{\nu}}_{\ensuremath{\tau}}$ oscillations with ${sin}^{2}2\ensuremath{\theta}g0.82$ and $5\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}4}l\ensuremath{\Delta}{m}^{2}l6\ifmmode\times\else\texttimes\fi{}1{0}^{\ensuremath{-}3}\mathrm{eV}{}^{2}$ at 90% confidence level.