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.     

On charm production at high energies

A number of new huge neutrino telescopes have been built, are being built, and are planned to be built all over the world. With these setups, cosmic neutrinos of high energies can be studied experimentally. Atmospheric neutrinos represent the main backgrounds to such experiments—namely, the atmospheric neutrinos determine how large a setup should be to measure diffuse cosmic neutrino fluxes or what angular resolution of a setup should be in order that searches for pointlike neutrino sources in the sky be successful. The atmospheric-neutrino fluxes are calculated in the present study. At high energies, the atmospheric-neutrino fluxes consist mostly of neutrinos produced in the atmosphere through charmed-particle decays. Three sources of information about charm production are used: (1) data obtained in accelerator experiments, (2) data on cosmicray muons, and (3) predictions of the NLO and QGSM QCD models for the charm-production at energies not available at modern accelerators. The uncertainties in the calculated fluxes of atmospheric neutrinos from charmed-particle decays are estimated to be at a level of 3–5 orders of magnitude.     

Fluxes of high- and ultrahigh-energy cosmic-ray muons

The positive excess of cosmic-ray muons at energies higher than 1 TeV is estimated taking into account the data obtained from accelerator experiments on the production of particle and antiparticles in proton-proton interactions at energies of ～20 TeV. The fluxes of cosmic-ray muons at energies up to ～10¹¹ GeV and the production functions of muon bremsstrahlung photons at different depths in the atmosphere are calculated with due regard for the contribution from the decay of J/ψ mesons. The analysis performed is based on the accelerator data and their extrapolation to higher energies.     

The possibility of searching for new physics in cosmic rays

One possible explanation of cosmic-ray energy spectrum behavior around the knee (3–5 PeV) by means of production of new heavy particles or a new state of matter is considered. It is shown that, in this case, a large excess of muons and neutrinos with energies of >100 TeV must be generated. The existing VHE muon experimental data are analyzed. Possible experiments on VHE muon investigations are discussed.     

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.     

Quark-gluon state of matter and positive excess of cosmic-ray muons at high energies

The problem of the relationship between the numbers of positively and negatively charged particles in the flux of cosmic-ray muons arriving at sea level with energies in excess of 0.1 TeV (up to 100 TeV) is discussed. It is shown that the formation of quark—gluon matter as the result of high-energy nuclear interactions leads to a reduction of the positive excess in cosmic-ray muons at the above energies. At the present time, the quark-gluon state of matter is studied in accelerator experiments at colliding-particle energies of up to √s = 200 GeV per nucleon. Estimates presented in this article for the positive excess of muons having energies of up to 3 or 4 TeV are based on available data from accelerator experiments; at higher muon energies, the respective estimates are based on extrapolating these data.     

Limits on neutrino emission from gamma-ray bursts with the 40 string IceCube detector

IceCube has become the first neutrino telescope with a sensitivity below the TeV neutrino flux predicted from gamma-ray bursts if gamma-ray bursts are responsible for the observed cosmic-ray flux above 10(18) eV. Two separate analyses using the half-complete IceCube detector, one a dedicated search for neutrinos from pγ interactions in the prompt phase of the gamma-ray burst fireball and the other a generic search for any neutrino emission from these sources over a wide range of energies and emission times, produced no evidence for neutrino emission, excluding prevailing models at 90% confidence.     

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.     

Medium energy neutrinos from solar flares

The production of neutrinos with energies higher than 0.1 GeV in the solar atmosphere during solar flares is discussed. Neutrinos and muons are generated in decays of π^+- mesons produced in nuclear interactions of accelerated solar flare protons with matter of the Sun. Muons themselves decay yielding neutrinos. These neutrinos could come to the Earth and be detected with neutrino telescopes. Estimations of fluxes of such neutrinos are given.     

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.     

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.     

Temperature effect of the integral flux of cosmic-ray muons at high energies

The temperature coefficients of the integral fluxes of cosmic-ray muons arriving at sea level vertically and horizontally with energies of 10², 10⁴, and 3 × 10⁶ GeV are calculated. Decays of pions, kaons, and charmed particles are considered as sources of muon generation in the atmosphere (according to current data on the generation cross sections of pions, kaons, and charmed particles in interactions between nucleons and the nuclei of atmospheric atoms, obtained in experiments on accelerators and in quantum chromodynamics models). The uncertainties in the generation cross sections of charmed particles are quite high.     

The LVD experiment at Gran Sasso

Summary The Large-Volume Detector (LVD) in the Gran Sasso underground Laboratory is a multipurpose detector consisting of a large volume of liquid scintillator (at present 562 tons are in data taking) interleaved with limited-streamer tubes. Several physical problems are investigated with LVD, the major being the search for neutrino bursts from gravitational stellar collapses in our Galaxy. In this paper we discuss some results on cosmic neutrinos and cosmic-ray muons obtained with the first of the five towers of LVD (operational since June 1992) and part of the second tower (operational since June 1994). The results of the search for supernovae neutrinos show that LVD is a neutrino observatory able to detect neutrinos of different flavours from gravitational stellar collapses in all our Galaxy, over a wide range of burst durations. Indeed, the carbon-based liquid-scintillator target gives a unique possibility to directly detect neutral- and charged-currents neutrino interactions with a very good signature. This characteristic of LVD allows us to make an indirect estimate of the neutrino rest mass and of neutrino oscillations from supernovae in our Galaxy. No evidence for burst candidates has been found in the data recorded from June 1992 to March 1995, for a total live time of 682 days and a total exposure of 613 tons per year. We present the results of a time coincidence analysis between low-energy signals, eventually due to neutrinos of different flavours, and γ-ray bursts (GRBs) detected by the BATSE experiment. This search covers the period from June 1993 to March 1995, during which 41 GRBs have been selected from the BATSE data. Since no excess of events in LVD has been found, upper limits on the neutrino fluxes are reported for (ν_e, p), and for neutral- and charged-currents neutrino interactions of different flavours with the C-nuclei of the scintillator. The muon intensity as a function of slant depth is presented. These measurements, obtained during a live time period of 11.556 hours, cover a slant depths range from about 3000 to about 20 000 hg/cm² of standard rock and extend over five decades of intensity. An interesting result is that the muon flux is independent of slant depth beyond a depth of about 14 000 hg/cm² of standard rock, and corresponds to near horizontal muons. This is direct evidence that this flux is due to atmospheric neutrinos interacting in the rock surrounding LVD.     

The potential for neutrino physics at muon colliders and dedicated high current muon storage rings

Conceptual design studies are underway for muon colliders and other high-current muon storage rings that have the potential to become the first true “neutrino factories”. Muon decays in long straight sections of the storage rings would produce precisely characterized beams of electron and muon type neutrinos of unprecedented intensity. This article reviews the prospects for these facilities to greatly extend our capabilities for neutrino experiments, largely emphasizing the physics of neutrino interactions.     

Muons and neutrinos in the cosmic radiation

Summary This report covers 86 papers presented in HE4 and HE5 sessions of the XXIV ICRC. The topics of the papers are atmospheric muons and neutrinos, muon bundles, horizontal air showers, ?muon astronomy?, neutrino oscillations, high-energy neutrinos and neutrinos from collapsing stars. Rapporteur talk given at the XXIV International Cosmic-Ray Conference, Rome, August 28–September 8, 1995.     

Super-high-energy neutrino spectra in the atmosphere derived from the latest JACEE, MSU, SOKOL and CRN primary spectrum usingZ-factors for p-air collisions estimated from Fermi national accelerator data

Summary The absolute spectra of atmospheric neutrinos in the vertical direction and at large zenith angle have been estimated directly from the primary cosmic-ray nucleon spectrum based on the latest JACEE, MSU, SOKOL and CRN data surveyed by Swordy. The Fermi National Accelerator Laboratory results for pp→K^±X, pp→K^±X and pp→pX inclusive reactions have been used for theZ-factor calculations for meson production and these were modified for p-air and A-A collisions. The derived muon and electron neutrino spectra at 0° and 89° from non-prompt meson decay are found comparable with the results of Volkova and Zatsepin, and Butkevichet al. An estimate of the prompt muon neutrino spectra at 0° and 89° fromtthe charmed-meson decay has been given along with the earlier results of different authors. The present result for muon neutrino spectra at zenith angles 0° and 89° is found in approximate agreement with the EAS-TOP results of the Gran Sasso group.     

Fluxes of cosmic-ray muons and atmospheric neutrinos at high energies

The problem of charm generation in the interactions of nucleons with nuclei of air atoms at energies inaccessible at present-day accelerators is discussed. Both experimental data on cosmic-ray muons and the predictions of QCD-based theoretical models are used in analyzing the behavior of the differential cross sections for charmed-particle production at high energies. The calculated fluxes of muons and neutrinos arriving at sea level both along the vertical and along the horizontal direction are presented, together with their approximations for the interval 2×10²–10¹⁰ GeV.     

Atmospheric neutrinos and discovery of neutrino oscillations

Neutrino oscillation was discovered through studies of neutrinos produced by cosmic-ray interactions in the atmosphere. These neutrinos are called atmospheric neutrinos. They are produced as decay products in hadronic showers resulting from collisions of cosmic rays with nuclei in the atmosphere. Electron-neutrinos and muon-neutrinos are produced mainly by the decay chain of charged pions to muons to electrons. Atmospheric neutrino experiments observed zenith-angle and energy dependent deficit of muon-neutrino events. Neutrino oscillations between muon-neutrinos and tau-neutrinos explain these data well. Neutrino oscillations imply that neutrinos have small but non-zero masses. The small neutrino masses have profound implications to our understanding of elementary particle physics and the Universe. This article discusses the experimental discovery of neutrino oscillations.     

TeV neutrinos and GeV photons from shock breakout in supernovae

We show that as a Type II supernova shock breaks out of its progenitor star, it becomes collisionless and may accelerate protons to energies >10 TeV. Inelastic nuclear collisions of these protons produce an approximately 1 h long flash of TeV neutrinos and 10 GeV photons, about 10 h after the thermal (10 MeV) neutrino burst from the cooling neutron star. A Galactic supernova in a red supergiant star would produce a photon and neutrino flux of approximately 10(-4) erg cm(-2) s(-1). A km(2) neutrino detector will detect approximately 100 muons, thus allowing to constrain both supernova models and neutrino properties.     

50 TeV HEGRA sources and infrared radiation

The recent observations of 50 TeV gamma radiation by HEGRA have the potential of determining the extragalactic flux of infrared radiation. The fact that radiation is observed in the range between 30 and 100 TeV sets an upper limit on the infrared flux, while a cutoff at E_γ ≈ 50 TeV fixes this flux with a good accuracy. If the intrinsic radiation is produced due to interaction of high energy protons with gas or low-energy target photons, then an accompaning high-energy neutrino flux is unavoidable. We calculate this flux and underground muon flux produced by it. The muon flux is dominated by muons with energies about 1 TeV and can be marginally detected by a 1 km² detector like an expanded AMANDA.