Recording of ultrahigh-energy astrophysical neutrinos

This review is devoted to the problems of recording ultrahigh-energy neutrinos produced in distant astrophysical sources and during the decay of supermassive particles. Prospects for the detection of neutrino fluxes are considered based on peculiarities of the propagation and interaction of ultrahigh-energy neutrinos. The operating and planned facilities designed to investigate neutrinos from various sources are described: neutrino telescopes recording neutrino interactions in natural water and ice volumes; ground-based arrays of detectors and optical telescopes onboard orbital space stations capable of detecting neutrino-triggered horizontal air showers. Instruments based on new principles of recording neutrinos with extremely high energies are considered: radio telescopes designed to observe Cherenkov radio emission from neutrino cascades originating in such radio-transparent natural environments as the atmosphere, salt domes, ice packs, and lunar regolith; underwater acoustic detectors. It is shown that putting new facilities into operation will allow neutrinos from most of the known astrophysical sources with energies differing by more than ten orders of magnitude, from 10¹² to 10²²–10²⁴ eV, to be recorded.     

Electromagnetic cascade showers with the LPM effect in standard rock initiated by extremely high-energy (1015 eV to 1021 eV) gamma-rays

Summary High-energy neutrinos produce finally high-energy electromagnetic cascade showers. For the detectio of high-energy neutrinos, it is necessary to examine the behaviour of the electromagnetic cascade showers in the higher-energy region. It is well known that the LPM effect plays a decisive role in the electromagnetic cascade shower development at higher energies. In the present paper, the behaviour of electromagnetic cascade showers including the LPM effect (LPM showers) in standard rock is examined using the calculational technique developed by Fujimaki and Misaki. In order to clarify the characteristics of LPM showers, similar calculations are also carried out for cascade showers in the absence of the LPM effect (BH showers). Comparisons between the two different kinds of cascade showers are made over electron transition curves, track lengths and fractional dissipated energies. Finally, the strong deviation of LPM showers from the normal BH showers is emphasized.     

Neutrino cross sections and future observations of ultrahigh-energy cosmic rays

We show that future detectors of ultrahigh-energy cosmic-ray neutrinos will be able to measure neutrino-nucleon cross section, sigma(nu N), at energies as high as 10(11) GeV or higher. We find that the flux of upgoing charged leptons per unit surface area produced by neutrino interactions below the surface is inversely proportional to sigma(nu N). This contrasts with the rate of horizontal air showers (HAS) due to neutrino interactions in the atmosphere, which is proportional to sigma(nu N). Thus, by comparing the HAS and upgoing air shower rates, the neutrino-nucleon cross section can be inferred. Taken together, upgoing and horizontal rates ensure a healthy total event rate, regardless of the value of sigma(nu N).     

Measuring clock jumps using pulsar timing

The Giant Radio Array for Neutrino Detection(GRAND) is a planned large-scale observatory of ultra-high-energy(UHE) cosmic particles, with energies exceeding 10~8 Ge V. Its goal is to solve the long-standing mystery of the origin of UHE cosmic rays. To do this, GRAND will detect an unprecedented number of UHE cosmic rays and search for the undiscovered UHE neutrinos and gamma rays associated to them with unmatched sensitivity. GRAND will use large arrays of antennas to detect the radio emission coming from extensive air showers initiated by UHE particles in the atmosphere. Its design is modular: 20 separate, independent sub-arrays, each of 10000 radio antennas deployed over 10000 km~2. A staged construction plan will validate key detection techniques while achieving important science goals early. Here we present the science goals, detection strategy, preliminary design, performance goals, and construction plans for GRAND.     

Astroparticle physics with high energy neutrinos: from AMANDA to IceCube

Kilometer-scale neutrino detectors such as IceCube are discovery instruments covering nuclear and particle physics, cosmology and astronomy. Examples of their multidisciplinary missions include the search for the particle nature of dark matter and for additional small dimensions of space. In the end, their conceptual design is very much anchored to the observational fact that Nature produces protons and photons with energies in excess of 10²⁰ eV and 10¹³ eV, respectively. The puzzle of where and how Nature accelerates the highest energy cosmic particles is unresolved almost a century after their discovery. The cosmic ray connection sets the scale of cosmic neutrino fluxes. In this context, we discuss the first results of the completed AMANDA detector and the science reach of its extension, IceCube. Similar experiments are under construction in the Mediterranean. Neutrino astronomy is also expanding in new directions with efforts to detect air showers, acoustic and radio signals initiated by super-EeV neutrinos. The outline of this review is as follows:

Introduction

Why kilometer-scale detectors?

Cosmic neutrinos associated with the highest energy cosmic rays

High energy neutrino telescopes: methodologies of neutrino detection

High energy neutrino telescopes: status

     

High energy physics in the atmosphere: phenomenology of cosmic ray air showers

The properties of cosmic rays with energies above 10⁶ GeV have to be deduced from the spacetime structure and particle content of the air showers which they initiate. In this review we summarize the phenomenology of these giant air showers. We describe the hadronic interaction models used to extrapolate results from collider data to ultra high energies, and discuss the prospects for insights into forward physics at the LHC. We also describe the main electromagnetic processes that govern the longitudinal shower evolution, as well as the lateral spread of particles. Armed with these two principal shower ingredients and motivation from the underlying physics, we provide an overview of some of the different methods proposed to distinguish primary species. The properties of neutrino interactions and the potential of forthcoming experiments to isolate deeply penetrating showers from baryonic cascades are also discussed. We finally venture into a terra incognita endowed with TeV-scale gravity and explore anomalous neutrino-induced showers.     

Pulsars as the most probable sources of ultrahigh-energy cosmic rays

The arrival directions of ultrahigh-energy extensive air showers detected at the Yakutsk extensive air shower array are considered. The maxima revealed in the distribution of the arrival directions of showers and doublets are found to correlate with the coordinates of pulsars located in the Galactic plane. It is shown that the three showers detected at the Yakutsk extensive air shower with the highest energies E > 10²⁰ eV correlate with the nearest pulsars.     

A search for decays of heavy neutrinos in the mass range 0.5–2.8 GeV

A search for decays of heavy neutrinos was conducted by the CHARM Collaboration in a prompt neutrino beam produced by dumping 400 GeV protons in a Cu target, and in the CERN wide-band neutrino beam produced by 400 GeV primary protons. No candidate event was found. In the beam-dump experiment heavy neutrinos have been assumed to be produced by mixing in charmed D meson decays. Neutrinos decaying into e⁺e⁻v_e, μ⁺e⁻v_μ, and μ⁺μ⁻v_μ were searched for. Limits of |U_ei|², |U_μi|² < 10⁻⁷ were obtained for neutrino masses around 1.5 GeV. In the wide-band experiment heavy neutrinos were assumed to be produced by neutral-current neutrino interactions in the CHARM calorimeter. Here a search was made for neutrinos decaying into a μ and hadrons. This experiment is sensitive to decays of neutrinos with mass in the range 0.5–2.8 GeV with limits of |U_μi|² < 3 × 10⁻⁴ for masses around 2.5 GeV. These measurements extend our previous results in the mass range 10–400 MeV.     

Methodological Issues of Gamma-Ray and Neutrino Searches at the Yakutsk Array

The method used to perform searches for extensive air showers (EAS) generated by neutral particles, such as high-energy gamma rays and astrophysical neutrinos, and the results of such searches are presented. A comprehensive analysis of relevant data, including those on EAS electrons, muons, and Cherenkov light and their time responses in scintillation and Cherenkov detectors, is performed for this purpose. An upper limit on the gamma-ray flux at the energies of 3 × 10¹⁸, 10¹⁹, and 3 × 10¹⁹ eV is set. A multivariate analysis of EAS properties of neutrino-induced air showers does not reveal neutrino-induced showers.     

On the sensitivity of the spatial-angular distribution of the Cherenkov light in extensive air showers to the mass composition of primary cosmic rays with energies of 10<Superscript>15</Superscript>–10<Superscript>16</Superscript> eV

This paper analyses the possibility of separating distinct groups of nuclei of primary cosmic rays with energies of 10¹⁵–10¹⁶ eV from the data on the spatial-angular distribution of Cherenkov light in extensive air showers. The paper shows that using an array of a few (3–4) telescopes with a moderately sized angular cell ∼0.5° placed at a distance ∼100 m from one another, one can achieve almost complete separation of the showers initiated by these nuclei (the Bayesian classification error is a few percentage points for the case of separating primary protons and nitrogen nuclei). The authors propose new parameters of the angular Cherenkov image that can greatly enhance the separability of the shower classes as compared to the approach based on the traditional parameters.     

Solar neutrino flux measurements by the Soviet-American gallium experiment (SAGE) for half the 22-year solar cycle

We present measurements of the solar neutrino capture rate on metallic gallium in the Soviet-American gallium experiment (SAGE) over a period of slightly more than half the 22-year solar cycle. A combined analysis of 92 runs over the twelve-year period from January 1990 until December 2001 yields a capture rate of 70.8 _?5.2 ^+5.3 (stat) _?3.2 ^+3.7 (sys) SNU for solar neutrinos with energies above 0.233 MeV. This value is slightly more than half the rate predicted by the standard solar model, 130 SNU. We present the results of new runs since April 1998 and analyze all runs combined by years, months, and bimonthly periods beginning in 1990. A simple analysis of the SAGE results together with the results of other solar neutrino experiments gives an estimate of (4.6±1.2)× 10¹⁰ neutrinos cm^?2 s^?1 for the flux of the electron pp neutrinos that reach the Earth without changing their flavor. The flux of the pp neutrinos produced in thermonuclear reactions in the Sun is estimated to be (7.6 ± 2.0) × 10¹⁰ neutrinos cm^?2 s^?1, in agreement with the value of (5.95±0.06)×10¹⁰ neutrinos cm^?2 s^?1 predicted by the standard solar model.     

Estimation of the PCR mass composition in the energy range 1017–1019 eV on the basis of multicomponent analysis of the characteristics of EASs detected at the Yakutsk array

The characteristics of longitudinal and radial extensive air shower development derived from the results of detection of the charged particle flux and Cherenkov light in extensive air showers at the Yakutsk array. To estimate the primary cosmic ray composition, a combination of the parameters X_max and ρ₆₀₀ and the database simulated using the CORSIKA code (QGSJET model) for showers generated by five types of nuclei (p, He, C, Si, Fe) in the energy range 10¹⁷–10¹⁹ eV were used. Application of the multicomponent method made it possible to divide the showers into three groups (p + He), C, and (Si + Fe) and estimate their percentage. The error in identifying nuclei in the energy range 10¹⁷–10¹⁸ eV does not exceed 30%.     

Salt neutrino detector for ultrahigh-energy neutrinos

Rock salt and limestone are studied to determine their suitability for use as a radio-wave transmission medium in an ultrahigh energy (UHE) cosmic neutrino detector. A sensible radio wave would be emitted by the coherent Cherenkov radiation from negative excess charges inside an electromagnetic shower upon interaction of a UHE neutrino in a high-density medium (Askar’yan effect). If the attenuation length for the radio wave in the material is large, a relatively small number of radio-wave sensors could detect the interaction occurring in the massive material. We measured the complex permittivity of the rock salt and limestone by the perturbed cavity resonator method at 9.4 and 1 GHz to good precision. We obtained new results of measurements at the frequency at 1.0 GHz. The measured value of the radio-wave attenuation length of synthetic rock salt samples is 1080 m. The samples from the Hockley salt mine in the United States show attenuation length of 180 m at 1 GHz, and then we estimate it by extrapolation to be as long as 900 m at 200 MHz. The results show that there is a possibility of utilizing natural massive deposits of rock salt for a UHE neutrino detector. A salt neutrino detector with a size of 2×2×2 km would detect 10 UHE neutrino/yr generated through the GZK process.     

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.     

A Study of Electromagnetic Cascade Showers with the LPM Effect in Water for the Detection of Extremely High Energy Neutrinos An application of the matrix method to LPM showers

The matrix method given by Fujimaki and Misaki is proved to be a powerful means for the calculations of electromagnetic cascade showers at extremely high energies. The method is essentially simple and has wide applications for the calculation of cascade showers. This method is used for the calculation of the cascade showers with the LPM effect in water, for the detection of extremely high energy neutrinos. The characteristics of LPM showers in water are extracted referring to cascade showers in the absence of the LPM effect.     

Simulation of muon-induced air showers affecting CMS tracking detectors

We study the propagation of energetic muons produced by ultrahigh energy cosmic rays which could penetrate the cavern of a giant experiment called Compact Muon Solenoid (CMS) at CERN. The present work is based on our previous simulation model proposed in [1]. We have improved this model by (1) eliminating the ambiguity via adding Landau-Pomeranchuk-Migdal effect to the Monte-Carlo code, (2) using different incidence angles of the simulated air showers, (3) defining the actual contents of the CMS cavern concrete. We estimate the energy spectrum of muons produced by air showers of primary protons and photons, which could be detected as a background in the CMS tracking detectors. Our results show that muons produced by air showers within the energy range 10¹⁷–10²⁰ eV injected to the CMS site could penetrate the cavern with cutoff energy 36.5 GeV. The article is published in the original.     

Study on the structure functions of electrons and the energy flow in the soft component of cosmic-ray extensive air showers

Summary Cosmic-ray air shower structure functions for the distance dependence of electron density in cosmic-ray air showers in the size range 10⁴⋎10⁸ have been computed for their intercomparison and comparison with Monte Carlo simulation results and measurements from recent experiments. The analysis has yielded the present status of theoretical structure functionsvis à vis experimental results and Monte Carlo simulation distributions. The effect of core location error on the lateral distribution of electrons is also discussed from the point of view of different theoretical and experimental results. The energy flow in the soft component of air showers of size ∼4·10⁵ has been evaluated within a ring of radius 10m about the axis of the showers.     

EMMA—a new underground cosmic-ray experiment

An experiment observing underground muons originating from cosmic-ray air showers is under preparation in the Pyhäsalmi mine, Finland. The aim is to cover an area of about 200–300 m², and the detector setup is capable of measuring the muon multiplicity and their lateral distribution. The detector is placed at a depth of about 85 m (corresponding about 240 m w.e.), which gives a threshold energy of muons of about 45 GeV. The detection of the multimuon events is motivated by partly unknown composition of the primary cosmic rays in the energy region of 10¹⁵–10¹⁶ eV, i.e., the knee region. In addition, by measuring only the higher energy muons of the air shower, the lowest energy muons being filtered out by the rock overburden, the data is sensitive also to the studies of the upper parts of the air shower. The experiment will be constructed mainly using drift chambers used previously in LEP detectors at CERN, but it can also be expanded using plastic scintillator detectors. The prototype detector is expected to be running in the beginning of 2006, and the full-size detector by the end of 2007.     

平均能量为2×1015eV的宇宙线入射方向研究

从1982年5月到1983年1月,悉尼大学的小型宇宙线观测阵列记录了多于17,000个能量为6×10¹⁴—5×10¹⁶eV的宇宙线广延大气簇射事例。使用谐波分析和X²检验法,对这些宇宙线的入射方向进行了研究,没有发现有意义的各向不同性。 关键词：     

Studying the muon and hadron components of extensive air showers with the Carpet-2 array

The method of separating muons and hadrons recorded by the Muon Detector of the Carpet-2 air shower array of Baksan Neutrino Observatory (Institute for Nuclear Research, Russian Academy of Sciences) is described. The results of studying characteristics of the muon and hadron components of extensive air showers (EAS) with N _e ≥ 10⁵ are presented. For the range of distances 40–55 m from shower axes the numbers of hadrons with energies higher than 30 GeV and muons with energies above 1 GeV are obtained as functions of the shower size N _e .