Cosmic-ray muon and atmospheric neutrino fluxes at very high energies

Estimates of cosmic-ray muon and atmospheric neutrino fluxes at TeV energies are obtained taking into account a “prompt” production of muons and neutrinos through charmed-particle decays and a “direct” lepton-pair production through the Drell-Yan mechanism and resonances. It is found that the contribution of charmed particles to the muon flux is equal to that from the conventional sources (pion and kaon decays) at 60 TeV, and the same equality can take place at 10 and 1 TeV for muon and electron neutrinos, respectively (for particles coming to sea level in the vertical direction). This “direct” production contribution to muon and neutrino fluxes is estimated very arbitrarily, but it cannot be excluded that this contribution is equal to that from the conventional source at energies of 0.5 and 0.05 PeV for muons and muon neutrinos, respectively. Currently, the estimates of the “prompt” and the “direct” contributions to cosmic-ray muons and atmospheric neutrinos are only qualitative. This is true especially for the “direct” contribution. Nevertheless, it seems reasonable to attract attention to these potentially important sources of atmospheric muons and neutrinos.     

Charm production and experimental data on cosmic neutrino flux

The results of calculation of atmospheric neutrino fluxes at sea level with energies up to 10⁷ GeV are presented. The calculations were performed within the empirical model based on modern data on inclusive cross sections of pion, kaon, and charmed particle production in nucleon-air nucleus interactions, obtained in experiments on accelerators up to nucleon energies of ～20 TeV. A comparison of the calculated and experimental data on cosmic muon neutrino fluxes measured on AMANDA II shows their agreement.     

Precision measurement of neutrino oscillation parameters at INO-ICAL detector

A magnetized Iron CALorimeter (ICAL) detector at the India-based neutrino observatory (INO) is used to study neutrino oscillation sensitivity using atmospheric muon neutrino source. The ICAL detector will be able to detect muon tracks and hadron showers produced by neutrino interactions with the iron target. We have performed precision measurement analysis for the atmospheric neutrino oscillation parameters with the muon neutrino events, generated by Monte Carlo NUANCE event generator. A marginalized χ² analysis based on reconstructed neutrino energy and muon zenith angle binning scheme has been performed to determine the sensitivity for the atmospheric neutrino mixing parameters, \(\sin ^{2}\theta _{23}\) and \(| {\Delta } m^{2}_{23}|\).     

Possible CP-violation effects in core-collapse supernovae

We study CP-violation effects when neutrinos are present in dense matter, such as outside the proto-neutron star formed in a core-collapse supernova. Using general arguments based on the Standard Model, we confirm that there are no CP-violating effects at the tree level on the electron neutrino and anti-neutrino fluxes in a core-collapse supernova. On the other hand significant effects can be obtained for muon and tau neutrinos even at the tree level. We show that CP-violating effects can be present in the supernova electron (anti-)neutrino fluxes as well, if muon and tau neutrinos have different fluxes at the neutrinosphere. Such differences could arise due to physics beyond the Standard Model, such as the presence of flavor-changing interactions.     

Searches for the appearance of \nu_\tau using neutrino beams from muon storage rings

We study the possibilities offered by muon storage rings for appearance experiments in order to determine masses and mixing angles for the and oscillations. The dependence of tau event rates on baseline, forward peaking of decay neutrinos with increasing energies, and average fluxes intercepted by detectors of various sizes is discussed. It is found that the baseline length does not significantly affect the rates for oscillations of such magnitudes as are suggested by the current atmospheric neutrino data. Subsequently, the effects of cuts on hadronic and wrong sign leptonic modes are computed and used to plot 90% CL contours for the parameter regions that can be explored in such experiments. The results show that even for modest muon beam energies, convincing coverage and verification of the Super Kamiokande parameters is possible. In addition, a very significant enlargement of present day bounds on the mixing parameters for neutrino oscillations of all types is guaranteed by these types of searches. Received: 4 April 2000 / Revised version: 22 July 2000 / Published online: 8 December 2000     

中微子质量和中微子振荡实验

本介绍中微子质量测量的历史和现状。介绍太阳中微子丢失实验的结果和大气μ中微子丢失实验结果。这些结果表明存在中微子振荡,即中微子具有质量。它是超出标准模型的信号。本还介绍了21世纪初研究中微子振荡的若干重要实验,例如长基线中微子振荡实验以及建造μ子 贮存环来产生高能电子中微子束进行中微子振荡的实验以及测量中微子振荡时的CP破坏的设想。     

Results from atmospheric neutrinos

With the announcement of new evidence for muon neutrino disappearance observed by the super-Kamiokande experiment, the more than a decade old atmospheric neutrino anomaly moved from a possible indication for neutrino oscillations to an apparently inescapable fact. The evidence is reviewed, and new indications are presented that the oscillations are probably between muon and tau neutrinos. Implications and future directions are discussed.     

Primary cosmic ray and muon measurements with CAPRICE

The WiZard Collaboration has performed several investigations of the cosmic ray muon component in the atmosphere. In this paper, we review the most recent results from the balloon-borne CAPRICE experiment and discuss their relevance in the context of the atmospheric neutrino observations.     

Atmospheric neutrino flux at INO,South Pole and Pyhäsalmi

We present the calculation of the atmospheric neutrino fluxes for the neutrino experiments proposed at INO, South Pole and Pyhäsalmi. Neutrino fluxes have been obtained using ATMNC, a simulation code for cosmic ray in the atmosphere. Even using the same primary flux model and the interaction model, the calculated atmospheric neutrino fluxes are different for the different sites due to the geomagnetic field. The prediction of these fluxes in the present Letter would be quite useful in the experimental analysis.     

中微子振荡实验——超出标准模型的实验检验（Ⅰ）

文章总结了中微子振荡实验在历史和现状,介绍了几个太阳中微子丢失实验的结果和几个大气μ中微子丢失实验结果,这些结果表明存在中微子振荡,即中微子具有质量,它是超出标准模型的信号,文章还介绍了21世纪初研究中微子振荡和若干重要实验,噬基线中微子振荡实验以及建造μ子贮存环来产生高能电子中微子束进行中微子振荡的实验以及测量中微子振荡时的CP破坏的设想。     

Discovery of atmospheric neutrino oscillations**

Atmospheric neutrinos are produced by cosmic ray interactions in the atmosphere. The zenith‐angle and energy dependence of the muon‐ and electron‐ neutrino events are observed in atmospheric neutrino experiments. Through these studies neutrino oscillations were discovered. In this article, studies of atmospheric neutrinos in the Kamiokande and Super‐Kamiokande experiments are described.     

Coincidence analysis in ANTARES: Potassium-40 and muons

The ANTARES neutrino detector, located deep underwater in Mediterranean sea, is currently almost complete and taking physics data. The amount of data collected so far allows for several kinds of neutrino studies. Yet, presently the principal task of the collaboration is to achieve thorough and precise understanding of the detector. Therefore, detector calibration and atmospheric muon studies are currently given high priorities. A new calibration technique, based on the use of natural background light in seawater, was recently invented. The method relies on correlated coincidences produced in triplets of ANTARES optical modules by Cherenkov light of beta-particles originated from ⁴⁰K decays. Based on similar ideas of coincidence analysis, a simple but powerful approach to atmospheric muon flux studies is currently being developed. The two methods and their role in the ANTARES experiment are briefly presented.     

High-energy spectra of atmospheric neutrinos

A calculation of the atmospheric high-energy muon neutrino spectra and zenith-angle distributions is performed for two primary spectrum parameterizations (by Gaisser and Honda and by Zatsepin and Sokolskaya) with the use of QGSJET-II-03 and SIBYLL 2.1 hadronic models. A comparison of the zenith angle-averaged muon neutrino spectrum with the data of Frejus, AMANDA-II, and IceCube40 experiments makes it clear that, even at energies above 100 TeV, the prompt neutrino contribution is not apparent because of the considerable uncertainties of the experimental data in the high-energy region.     

High energy neutrinos from galactic sources

Analytical expressions are derived which allow to calculate flux densities of energetic neutrinos from hypothetical galactic sources, consisting of a proton accelerator and a dilute gas beam dump. The same formalism is used to calculate atmospheric muon and μ-neutrino fluxes. From the results, rates of upward going muons, both from the atmosphere and galactic sources, are computed and detection limits for neutrino emitters in the sky are established. Finally, the background in a surface detector, caused by scattered muons and charm decays in the rock, is estimated for the case of a flat surrounding.     

Search for extraterrestrial point sources of neutrinos with AMANDA-II

We present the results of a search for point sources of high-energy neutrinos in the northern hemisphere using AMANDA-II data collected in the year 2000. Included are flux limits on several active-galactic-nuclei blazars, microquasars, magnetars, and other candidate neutrino sources. A search for excesses above a random background of cosmic-ray-induced atmospheric neutrinos and misreconstructed downgoing cosmic-ray muons reveals no statistically significant neutrino point sources. We show that AMANDA-II has achieved the sensitivity required to probe known TeV gamma-ray sources such as the blazar Markarian 501 in its 1997 flaring state at a level where neutrino and gamma-ray fluxes are equal.     

Neutrino spectrum from theory and experiments

The observed deficits in the solar and atmospheric neutrino fluxes along with the accelerator results on neutrino oscillations significantly constrain possible mass and mixing patterns among neutrinos. We discuss possible patterns emerging from the experimental results and review theoretical attempts to understand them.     

BESS data on primary cosmic rays and muons

We have measured absolute fluxes of primary protons, helium nuclei and atmospheric muons with the BESS spectrometer. Precise measurement of these cosmic-ray particles is indispensable for improving the accuracy in the atmospheric neutrino calculations.     

L/E-flatness of the electron-like event ratio, in Super-Kamiokande and a degeneracy, in neutrino masses

We show that the L/E-flatness of the electron-like event ratio in the Super-Kamiokande atmospheric neutrino data implies the equality of the expectation values for the muon and tau neutrino masses. We establish this result by obtaining a set of three constraints on the neutrino-oscillation mixing matrix as contained in the indicated flatness. The resulting 3×3 neutrino-oscillation matrix depends only on one angle. A remarkable result that follows directly from this matrix is the consistency between the mixing angles observed by LSND and Super-Kamiokande.     

Nuclear effects on lepton polarization in charged-current quasielastic neutrino scattering

We use a correlated local Fermi gas (LFG) model, which accounts also for long distance corrections of the RPA type and final-state interactions, to compute the polarization of the final lepton in charged-current quasielastic neutrino scattering. The present model has been successfully used in recent studies of inclusive neutrino nucleus processes and muon capture. We investigate the relevance of nuclear effects in the particular case of τ polarization in tau-neutrino induced reactions for several kinematics of relevance for neutrino oscillation experiments.     

Tau neutrinos favored over sterile neutrinos in atmospheric muon neutrino oscillations

The previously published atmospheric neutrino data did not distinguish whether muon neutrinos were oscillating into tau neutrinos or sterile neutrinos, as both hypotheses fit the data. Using data recorded in 1100 live days of the Super-Kamiokande detector, we use three complementary data samples to study the difference in zenith angle distribution due to neutral currents and matter effects. We find no evidence favoring sterile neutrinos, and reject the hypothesis at the 99% confidence level. On the other hand, we find that oscillation between muon and tau neutrinos suffices to explain all the results in hand.