Atmospheric Neutrino Flux Research Articles

Leading order textures for lepton mass matrices

In theories with three light neutrinos, certain simplicity assumptions allow the construction of a complete list of leading order lepton mass matrices. These matrices are consistent with ${m}_{\ensuremath{\tau}}\ensuremath{\ne}0,\ensuremath{\Delta}{m}_{12}^{2}\ensuremath{\ll}\ensuremath{\Delta}{m}_{23}^{2},{\ensuremath{\theta}}_{23}\ensuremath{\sim}O(1)$ and ${\ensuremath{\theta}}_{13}=0,$ as suggested by measurements of atmospheric and solar neutrino fluxes. The list contains twelve generic cases: two have three degenerate neutrinos, eight have two neutrinos forming a Dirac state, and in only two cases is one neutrino much heavier than the other two. For each of these twelve generic cases the possible forms for the perturbations which yield ${m}_{\ensuremath{\mu}}$ are given. Ten special textures are also found.

Fluxes of atmospheric neutrinos and related cosmic rays

The atmospheric neutrino beam simultaneously spans a range of pathlengths from ten to ten thousand kilometers, which correspond respectively to downward- and upward-going neutrinos. As with any neutrino oscillation experiment, also in this case the interpretation of the data depends on a detailed knowledge of the neutrino beam. The ingredients are the primary spectrum of cosmic-ray nucleons, the geomagnetic fields in which the charged particles propagate and the properties of interactions of hadrons in the atmosphere. In this talk I review the status of calculations in light of the recent evidence for neutrino oscillations from Super-Kamiokande.

Uncertainty of the atmospheric neutrino fluxes

The uncertainty in the calculation of atmospheric neutrino fluxes is studied. The absolute value of atmospheric neutrino fluxes is sensitive to variation of the primary cosmic ray flux model and/or the interaction model. However, the ratios between different kind of neutrinos stay almost unchanged with these variations. It is unlikely that the anomalous ratio ( ν μ ν e ) obs ( ν μ ν e ) MC reported by Kamiokande and Super-Kamiokande is caused by the uncertainty of predicted atmospheric neutrino fluxes.

Tau neutrino fluxes from atmospheric charm

We present an evaluation of the atmospheric tau neutrino flux in the energy range between $10^2$ and $10^6$ GeV. The main source of tau neutrinos is from charmed particle production and decay. The $\nu_\tau N\to \tau X$ event rate for a detector with a water equivalent volume of 1 km$^3$ is on the order of 60-100 events per year for $E_\tau>100$ GeV, reducing to 18 events above 1 TeV. Event rates for atmospheric muon neutrino oscillations to tau neutrinos are also evaluated.

Active-active and active-sterile neutrino oscillation solutions to the atmospheric neutrino anomaly

We perform a fit to the full data set corresponding to 33.0 kt-yr of data of the Super-Kamiokande experiment as well as to all other experiments in order to compare the two most likely solutions to the atmospheric neutrino anomaly in terms of oscillations in the ν μ → ν τ and ν μ → ν s channels. Using state-of-the-art atmospheric neutrino fluxes we have determined the allowed regions of oscillation parameters for both channels. We find that the Δm 2 values for the active-sterile oscillations (both for positive and negative Δm 2) are higher than for the ν μ → ν τ case, and that the increased Super-Kamiokande sample slightly favours ν μ → ν τ oscillations over oscillations into a sterile species ν s , ν μ → ν s , and disfavours ν μ → ν e . We also give the zenith angle distributions predicted for the best fit points in each of the possible oscillation channels. Finally we compare our determinations of the atmospheric neutrino oscillation parameters with the expected sensitivities of future long-baseline experiments K2K, MINOS, ICARUS, OPERA and NOE.

Textures for atmospheric and solar neutrino oscillations

A large θ μτ mixing angle, together with hierarchies in the neutrino Δ m 2 and in the charged lepton masses, place a significant restriction on the textures of the lepton mass matrices. In theories with three light neutrinos, a simple hypothesis leads to a complete list of four zeroth-order textures for lepton mass matrices is found: three for neutrinos which naturally yield θ μτ ≈1 with vanishing θ eτ and Δ m 2 ⊙, and one for charged leptons which naturally yields θ μτ ≈1 with m e = m μ = θ eτ =0. These textures provide suitable starting points for constructing theories which account for both atmospheric and solar neutrino fluxes. Using flavor symmetries, two schemes for such lepton masses are found, and example constructions exhibited.

A new calculation of atmospheric neutrino flux: the FLUKA approach

Preliminary results from a full 3-D calculation of atmospheric neutrino fluxes using the FLUKA interaction model are presented and compared to previous existing calculations. This effort is motivated mainly by the 3-D capability and the satisfactory degree of accuracy of the hadron-nucleus models embedded in the FLUKA code. Here we show examples of benchmarking tests of the model with cosmic ray experiment results. A comparison of our calculation of the atmospheric neutrino flux with that of the Bartol group, for E ν > 1 GeV, is presented.

Nearly degenerate mass and bimaximal mixing of neutrinos in the SO(3) gauge model of leptons

A realistic scheme for masses and mixing of leptons is investigated in the model with gauged SO(3) lepton flavor symmetry. Within this scheme, a nearly bimaximal neutrino mixing pattern with a maximal CP-violating phase is found to be the only possible solution for reconciling both solar and atmospheric neutrino flux anomalies. Three Majorana neutrino masses are nearly degenerate and large enough to play a significant cosmological role. Lepton flavor-violating effects via SO(3) gauge interactions can be as large as the present experimental limits. Masses of the SO(3) gauge bosons are bounded to be above 24 TeV when the SO(3) gauge boson mixing angle $\theta_{F}$ and coupling constant $g'_{3}$ are taken to be the same as those ( $\theta_{W}$ and g) in the electroweak theory.

Oscillations of solar and atmospheric neutrinos

Motivated by recent results from SuperKamiokande, we study both solar and atmospheric neutrino fluxes in the context of oscillations of the three known neutrinos. We aim at a global view which identifies the various possibilities, rather than attempting the most accurate determination of the parameters of each scenario. For solar neutrinos we emphasise the importance of performing a general analysis, independent of any particular solar model and we consider the possibility that any one of the techniques --- chlorine, gallium or water Cerenkov --- has a large unknown systematic error, so that its results should be discarded. The atmospheric neutrino anomaly is studied by paying special attention to the ratios of upward and downward going nu_e and nu_mu fluxes. Both anomalies can be described in a minimal scheme where the respective oscillation frequencies are widely separated or in non-minimal schemes with two comparable oscillation frequencies. We discuss explicit forms of neutrino mass matrices in which both atmospheric and solar neutrino fluxes are explained. In the minimal scheme we identify only two `zeroth order' textures that can result from unbroken symmetries. Finally we discuss experimental strategies for the determination of the various oscillation parameters.

Study of the atmospheric neutrino flux in the multi-GeV energy range

The flavor ratio of the atmospheric neutrino flux and its zenith angle dependence have been studied in the multi-GeV energy range using an exposure of 25.5 kiloton-years of the Super-Kamiokande detector. By comparing the data to a detailed Monte Carlo simulation, the ratio ( μ/ e) DATA/( μ/ e) MC was measured to be 0.66±0.06(stat.)±0.08(sys.). In addition, a strong distortion in the shape of the μ-like event zenith angle distribution was observed. The ratio of the number of upward to downward μ-like events was found to be 0.52 +0.07 −0.06(stat.)±0.01(sys.), with an expected value of 0.98±0.03(stat.)±0.02(sys.), while the same ratio for the e-like events was consistent with unity.

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.

Update on atmospheric neutrinos

We discuss the impact of recent experimental results on the determination of atmospheric neutrino oscillation parameters. We use all published results on atmospheric neutrinos, including the preliminary large statistics data of Super-Kamiokande. We re-analyze the data in terms of both $\nu_\mu \to \nu_\tau$ and $\nu_\mu \to \nu_e$ channels using new improved calculations of the atmospheric neutrino flux. We compare the sensitivity attained in atmospheric neutrino experiments with those of accelerator and reactor neutrino oscillation searches, including the recent Chooz experiment. We briefly comment on the implications of atmospheric neutrino data in relation to future searches for neutrino oscillations with long baselines, such as the K2K, MINOS, ICARUS and NOE experiments.

Measurement of the atmospheric muon neutrino flux with the macro detector

The flux of muon neutrinos in the 1 – 1000 GeV range has been measured with the MACRO underground detector. The measurement has been performed by means of the time-of-flight method to separate upward-going muons coming from neutrino interactions in the surrounding rock from downward-going muons coming directly from cosmic ray cascades. The analysis results for data collected since March 1989 up to November 1996 are summarized. The zenith angular dependence of the measured upward-going muon flux is compared with the expected one assuming the Bartol atmospheric neutrino flux. Also upward-going muons generated inside the detector have been detected.

Case for Neutrino Mass Gathers Weight

Case for Neutrino Mass Gathers Weight

Clusters of Galaxies as Storage Room for Cosmic Rays

It is demonstrated that clusters of galaxies are able to keep cosmic rays for a time exceeding the age of the universe. This phenomenon reveals itself by the production of the diffuse flux of high-energy gamma and neutrino radiation due to the interaction of the cosmic rays with the intracluster gas. The produced flux is determined by the cosmological density of baryons, Ωb, if a large part of this density is provided by the intracluster gas. The signal from relic cosmic rays has to be compared with the flux produced by the late sources, which can be considered as a background in the search for cosmic-ray production in the past. We calculate this flux considering the normal galaxies and active galactic nuclei (AGNs) in the clusters as the sources of cosmic rays. Another potential cosmic-ray source is the shock in the gas accreting to a cluster. We found that this background is relatively high: the diffuse fluxes produced by relic cosmic rays are of the same order of magnitude that can be expected from AGNs in the clusters. In all cases the predicted diffuse gamma-ray flux is smaller than the observed one, and the diffuse neutrino flux can be seen as the small bump at E ~ 106 GeV over the atmospheric neutrino flux. A bright phase in the galaxy evolution can be a source of the relic cosmic rays in clusters, revealing itself by diffuse gamma and neutrino radiation. We found that the observation of a signal from the bright phase is better for an individual cluster.

Three-flavor atmospheric neutrino anomaly

We investigate the indications of flavor oscillations that come from the anomalous flavor composition of the atmospheric neutrino flux observed in some underground experiments. We study the information coming from the neutrino-induced $\ensuremath{\mu}$-like and $e$-like events both in the sub-GeV energy range (Kamiokande, IMB, Fr\'ejus, and NUSEX experiments) and in the multi-GeV energy range (Kamiokande experiment). First we analyze all the data in the limits of pure ${\ensuremath{\nu}}_{\ensuremath{\mu}}\ensuremath{\leftrightarrow}{\ensuremath{\nu}}_{\ensuremath{\tau}}$ and ${\ensuremath{\nu}}_{\ensuremath{\mu}}\ensuremath{\leftrightarrow}{\ensuremath{\nu}}_{e}$ oscillations. We obtain that ${\ensuremath{\nu}}_{\ensuremath{\mu}}\ensuremath{\leftrightarrow}{\ensuremath{\nu}}_{e}$ oscillations provide a better fit, in particular, to the multi-GeV data. Then we perform a three-flavor analysis in the hypothesis of dominance of one neutrino square mass difference ${m}^{2}$ implying that the neutrino mixing is parametrized by two angles $(\ensuremath{\psi},\ensuremath{\varphi})\ensuremath{\in}[0,\ensuremath{\pi}/2]$. We explore the space ${(m}^{2},\ensuremath{\psi},\ensuremath{\varphi})$ exhaustively, and find the regions favored by the oscillation hypothesis. The results are displayed in a form suited to the comparison with other flavor oscillation searches at accelerator, reactor, and solar $\ensuremath{\nu}$ experiments. In the analysis, we pay particular attention to the Earth matter effects, to the correlation of the uncertainties, and to the symmetry properties of the oscillation probability.

Comparison of atmospheric neutrino flux calculations at low energies.

We compare several different calculations of the atmospheric neutrino flux in the energy range relevant for contained neutrino interactions, and we identify the major sources of difference among the calculations. We find nothing that would affect the predicted ratio of $\nu_e/\nu_\mu$, which is nearly the same in all calculations. Significant differences in normalization arise primarily from different treatment of pion production by interactions of protons in the atmosphere. Different assumptions about the primary spectrum and treatment of the geomagnetic field are also of some importance.

Charm production and high energy atmospheric muon and neutrino fluxes

Production of muons and neutrinos in cosmic ray interactions with the atmosphere has been investigated with Monte Carlo models for hadronic interactions. The resulting conventional muon and neutrino fluxes (from π and K decays) agree well with earlier calculations, whereas our prompt fluxes from charm decays are significantly lower than earlier estimates. Charm production is mainly considered as a well defined perturbative QCD process, but we also investigate a hypothetical non-perturbative intrinsic charm component in the proton. The lower charm rate implies better prospects for detecting very high energy neutrinos from cosmic sources.

Atmospheric neutrino flux above 1 GeV.

In this paper we extend an earlier calculation of the flux of atmospheric neutrinos to higher energy. The earlier calculation of the neutrino flux below 3 GeV has been used for calculation of the rate of contained neutrino interactions in deep underground detectors. The fluxes are needed up to neutrino energies of 10 TeV to calculate the expected rate of neutrino-induced muons passing into and through large, deep detectors. We compare our results with several other calculations, and we evaluate the uncertainty in the rate of neutrino-induced muons due to uncertainties in the neutrino flux. \textcopyright{} 1996 The American Physical Society.

Limits on the flux of very high energy neutrinos with the Fréjus detector

The final data set of muons recorded with the Fréjus detector has been analyzed to determine the atmospheric neutrino ν μ -flux. From the depth intensity relation of the muon flux a region of almost horizontal neutrino induced muons has been identified. The measurement of the energy loss inside the detector of these through-going muons allows a search for deviations from the expected energy spectrum of the atmospheric neutrinos with two independent methods. No evidence of any extra ν μ -flux at energies > 1 TeV has been found thus enabling significant limits to be set on the extragalactic ν μ -flux predicted by several models of cosmological sources. These limits do not depend on the particular atmospheric neutrino flux model considered.