Relic neutrino nu_r light masses clustering in Galactic and Local Hot Dark Halos act as a beam dump calorimeter. Ultra High Energy nu, above ZeV, born by AGNs, GRBs at cosmic edges, overcoming the Greisen, Zatsepin, Kuzmin (GZK) cut-off, may hit near Z resonance and WW-ZZ channels energies: their showering into nucleons and gamma Ultra High Cosmic Ray (UHECR) fit observed data . Any tiny neutrino mass splitting may reflect into a twin bump at highest GZK energy cut-off. The lighter the neutrino masses the higher the Z-Showering cut-off. The Z or WW,ZZ showering might explain a peculiar clustering in observed UHECR spectra at 10¹⁹, 2x10¹⁹, 4x10¹⁹ eV found recently by AGASA. Coincidence of clustered UHECR with highest gamma BLac sources, originated either by neutral and charged particles (Q=0,+1,-1) is well tuned to Z-Showering Scenario. Additional prompt TeVs signals occur offering a natural solution of growing Infrared-TeV cut-off paradoxes related to distant TeV BLac sources and a GRB at TeV energy. Electromagnetic Cascades tail may explain correlation found between GeV-EGRET Sources and UHECR. Such UHE v Astrophysics might trace near GZK energy into Horizontal Tau Air-Showers originated by the UHE v_τ Earth-Skimming in wide Corona Earth Crust around the observer; their consequent τ escape and decay upward in flight . These Upward and Horizontal τ Air-Showers UPTAUS, HORTAUS, monitor huge volumes from high mountains as well as observing from planes, balloons and satellites. HORTAUS from mountains observe corona masses at UHE v EeVs energies comparable to few km³, while from satellites at orbit altitudes, at GZK energies E_nu≥ 10¹⁹ eV, their corresponding Horizontal Corona Masses may even exceed 150 km³. The expected event rate may exceed a dozen of event a year in Z-WW Showering model from satellite.

The Large Area Air Shower (LAAS) group has been performing a network observation of extensive air showers (EAS) since 1996 in Japan. Ten compact EAS arrays are operating simultaneously at distant stations (up to ≈1000 km) and detecting EAS with mean energy of ≈10¹⁵ eV. Each station has 4--12 scintillation counters and a Global Positioning System (GPS), which provides time stamps of EAS triggers with an accuracy of 1μs. As a consequence of the comparable time stamps, uniformly-adjusted detectors and a standardized data format among all stations, we can treat the independent observations as a gigantic EAS detector system as a whole. The primary purpose of the network observation is to study large-scale correlations in ultra-high-energy cosmic rays. On the other hand, three nearby stations within 1~km distance at Okayama area have a possibility to detect extremely-high-energy EAS (≈10¹⁹ eV) as coincident triggers of the three stations. The present status of the network and some results from computer simulations are reported here.

Large-scale coincidences of extensive air showers (EAS) have been searched for with the aim of detecting signals from extreme short bursts of any point source in the universe. In this analysis, the network observation of EAS by distant stations is elaborately treated as a 'cosmic ray interferometer'. Each station is independently operating, but the Global Positioning System provides accurate time stamps to compare arrival times of EAS among the stations. Signals from burst activities can be extracted out of a sea of background cosmic rays in two steps: (i) picking out EAS pairs with very small arrival time differences and angular distances, (ii) examining the interference between the EAS pair based on the arrival time difference and the station distance. Datasets collected simultaneously by five stations of the Large Area Air Shower (LAAS) group during 1996--2002 were analyzed in this paper. We found three EAS pairs (Ε≈10^14-16eV) with extremely small arrival time differences (~100μs) and very small angular distances (≤10°). Arrival directions of two EAS pairs out of the three pointed to the Crab Nebula, suggesting that they were induced by a bundle of ultra-high-energy γ-rays from extreme short bursts of the object. However, the significances of them are not enough yet.

A new, small-scale, detector utilizing the finite thickness of air-shower "pancakes" has been developed and operated on the roof of the physics building at the University of Minnesota. (MR. CRATE = Minnesota Rooftop Cosmic-Ray Air-shower Timing Experiment). Such techniques were pioneered by Linsley and collaborators, carried forth in a variety of forms through the 1970s-80s, and with differing technologies by Watson and colleagues. The primary interest in such detector is the ability to use timing of the air shower to allow the array to trigger on events that fall outside of the array. In principal, one can use a single detector to observe air showers out to a distance at which the detector runs out of statistics. The Mark-I detector was simply that. More extensive detectors using these techniques have also been designed and built with an eye towards incorporating them into existing underground or surface air shower detectors. Preliminary results and design studies will be discussed.

The main aim of the KASCADE extensive air shower (EAS) experiment is the determination of the chemical composition of cosmic rays in the energy range around and above the knee at E_k ≈ 3 PeV. A large number of observables are measured simultaneously for each individual event, by the combination of various detection techniques for the electromagnetic, the muonic, and the hadronic component of the extensive air showers. Detailed investigations have been performed with the data measured by the KASCADE experiment since the start of data taking at the end of 1995. The results allow to evaluate hadronic interaction models, used in simulations to interpret air shower data. The all-particle spectrum of cosmic rays and their mass composition, as well as individual spectra for groups of elements have been reconstructed in the energy range between 10¹⁵ and 10¹⁷ eV . The results suggest, the knee in the all-particle cosmic-ray energy spectrum is caused by a rigidity-dependent cut-off of individual element groups. To improve the statistics around 10¹⁷ eV, where the “iron knee” in the cosmic ray spectrum is indicated in our data, the KASCADE experiment has recently been extended to KASCADE-Grande by a large collecting area (0.5km²) electromagnetic array, contributed from the former EAS-TOP experiment. The Grande part will cover the primary energy range 10¹⁶ eV<E₀<10¹⁸ eV, overlapping with KASCADE around 10¹⁶ eV, thus providing a continuous information from 3•10¹⁴ eV to 10¹⁸ eV. In addition, new technologies in detecting radio emission from cosmic ray air showers will be tested by an array of antennas (LOPES project) at the site of KASCADE.

The California HIgh school Cosmic ray ObServatory (CHICOS) is a collaborative project involving Caltech, Cal State Northridge, UC Irvine, and local high schools to site a large array of particle detectors in Southern California. The detectors are located on school rooftops, and utilize the power and network infrastructure available at the schools. The main scientific goal is to study cosmic rays at ultra-high energies E>10¹⁹ eV. We have fielded a total of 23 sites so far, and are beginning to collect data as we continue to deploy additional sites. We have observed our first evidence of extended air showers in coincidence with a local high school. The anticipated performance of the initial array and the potential for future expansion will be discussed.

The NEMO (NEutrino Mediterranean Observatory) collaboration is conducting an intense activity to develop technical solutions for the deployment of km³ scale neutrino detector in the Mediterranean Sea. The study of underwater networks of electro optical cables and connectors, mechanical layout and data transmission, is conducted together with leading companies in the field of submarine operations. The collaboration has also selected and characterised an optimal marine site in the region of Capo Passero at 3300 m depth, near the Sicilian Coasts. In addition, during year 2001, the collaboration has equipped a Test Site facility 28 km offshore the town of Catania. The facility will be fundamental for prototyping mechanical structures and data transmission systems.

High energy neutrino sources of astronomical origin are sought with data from the Super-Kamiokande-I detector. In this search, upward going muons with a minimum track length of 7m are used. During the first 5 years of operation, we have accumulated 2331 such events, of which 452 stopped in the detector and the rest passed through. This search, using the entire sample of upward going muon data from SK-I detector, revealed no statistically significant neutrino sources, setting new flux limits on astronomical neutrino sources.

The Southern Hemisphere site of the Pierre Auger Observatory is now under construction in Argentina by a collaboration of 50 institutions in 16 countries. The objective of the Auger Project is to make a high statistics measurement of cosmic rays above 10¹⁹ eV. The observatory will record extensive air showers induced by these cosmic rays incident on the atmosphere. The measurement will include energy, direction and composition of the primary particles. The engineering phase is now complete and full construction has begun. The search for the source of the highest energy cosmic rays is one of the most interesting problems in astrophysics. Following the discovery of the cosmic microwave background, Greisen and, independently, Zatsepin and Kuzmin realized hat this background radiation would make space opaque to cosmic rays of very high energy. Nevertheless over the past 30 years several tens of events were recorded with energies above the Greisen, Zatsepin, Kuzmin (GZK) cutoff (about 5×10¹⁹ eV) including a number above 10²⁰ eV. These events present a conundrum. Because of the GZK cut off these super high-energy events must come from nearby, less than about 50 Mpc. In addition the cosmic acceleration mechanism for achieving these energies is very difficult to conceive. Yet, even though particles of these energies are only slightly deflected by galactic and extragalactic magnetic fields, none clearly points back to a source sufficiently violent to a be a candidate source. The Auger Observatory finished its engineering development phase at the end of 2001. The “Engineering Array” consists of 40 surface particle detector stations and two prototype air fluorescence telescopes. The Observatory, when complete, will have a 1600 detector surface array covering 3000 km**2 overlooked by 24 fluorescence telescopes. The Engineering Array has demonstrated that all of the detector systems perform as well or better than expected. Recently the Observatory has recorded a number of cosmic ray events simultaneously with both the fluorescence and surface detectors.

The Pierre Auger Observatory is optimized to study the cosmic ray spectrum in the region of the Greisen-Zatsepin-Kuz'min (GZK) cutoff, i.e.cosmic rays with energies of ~10²⁰eV. Cosmic rays are detected as extensive air showers. To measure these showers each Auger site combines a 3000sq-km ground array with air fluorescence telescopes into a hybrid detector. Our design choice is motivated by the heightened importance of the energy scale, and related systematic uncertainties in shower energies, for experiments investigating the GZK cutoff. This paper focuses on the optical calibration of the Auger fluorescence telescopes. The optical calibration is done three independent ways: an absolute end-to-end calibration using a uniform, calibrated intensity, light-source at the telescope entrance aperture, a component by component calibration using both laboratory and in-situ measurements, and Rayleigh scattered light from external laser beams. The calibration concepts and related instrumentation are summarized. Results from the 5-month engineering array test are presented.

The Auger Observatory southern site's surface detector will consist of 1600 water Cerenkov detectors spaced 1.5 km apart on a 3000 km² site in Mendoza, Argentina. A discussion of the design and results from deployment of an engineering array are presented.

The Pierre Auger Project is an international effort to make a high statistics study of cosmic rays at the highest energies. To obtain full sky coverage two nearly identical air shower detectors will be constructed, one to be placed in the Northern Hemisphere and one in the Southern Hemisphere. Each installation will have an array of about 1,600 particle detectors spread over 3,000 km². Atmospheric fluorescence telescopes placed within and on the boundaries of the surface array will record showers that strike the array. The two air shower detector techniques working together form a powerful, hybrid, instrument for these studies. The results from both air fluorescence and surface detectors, on their own, have been quite notable, but are also notable in their disagreement with each other. Hence the concept of an experiment unifying the two approaches to the highest-energy cosmic rays. It is the design of the hybrid nature of the experiment, the analysis of events with hybrid information, and some preliminary results that will be discussed here.

Rock salt and limestone are studied to determine their suitability for use as a radio wave transmission medium in an ultra high energy (UHE) cosmic neutrino detector. Sensible radio-wave would be emitted the Askar'yan effect (coherent Cherenkov radiation from negative excess charges in an electromagnetic shower) in the interaction of the UHE neutrinos with the high-density medium. If the attenuation length in the material is large, relatively small number of radio-wave detector could detect the interactions happened in the massive material. We have been measured the complex permittivity of the rock salts and limestones by a free space method and a perturbational resonator method at 9.4GHz. In this paper, we show the data for new limestone samples from Mt. Jura in France at 9.4GHz and the results of preliminarily measurements of the frequency dependence at 7-12GHz .The measured value of the radio-wave attenuation lengths of the rock salt sample from the Asse mine in Germany is longer than 3.3m at 9.4 GHz and then under the assumption of constant tanδ with respect to frequency, we estimate it by extrapolation to be longer than 310 m at 100 MHz. The results show that there is a possibility to utilize natural massive deposits such as rock salt for a UHE neutrino detector.

We conduct a search for the coherent Cherenkov radiation (from negative charge excess), induced by high energy cosmic-rays. As a medium for detecting Cherenkov radiation we use a 20 ton target of synthetic rock salt contained within a scintillation counter cosmic-ray hodoscope. Two parallel arrays of crossed bow tie antennas are put inside the salt bed and used as a detection tool. We also present preliminary results from beam tests of the approach done at SLAC.

We report on results from 80 hours of livetime with the Goldstone Lunar Ultra-high energy neutrino Experiment (GLUE). The experiment searches for microwave pulses (width ≤ 10 ns) from the lunar regolith, appearing in coincidence at two large radio telescopes separated by 22 km and linked by optical fiber. Such pulses would arise from subsurface electromagnetic cascades induced by interactions of up-coming ~ 100 EeV neutrinos in the lunar regolith. Triggering on a timing coincidence between the two telescopes significantly reduces the terrestrial interference background, allowing operation at the thermal noise level. No unambiguous candidates are yet seen. We report on limits implied by this non-detection, based on new Monte Carlo estimates of the efficiency.

Upper limits are presented on the diffuse flux of ultra-high energy neutrinos, based on analysis of data taken by the RICE experiment during August, 2000. The RICE receiver array at South Pole monitors cold ice for radio-wavelength Cherenkov radiation resulting from neutrino-induced in-ice showers. For energies above 1 EeV, RICE monitors over 25 km³ sr. We discuss limits based on both hadronic and electromagnetic showers.

Ultra-high Energy cosmic neutrinos will produce a detectable pulse of RF radiation when they interact in solid media. Large rock salt formations, which are highly transparent to RF radiation, may serve as the medium for detectors searching for astrophysical neutrino sources. It is possible to instrument such formations with antennas to produce a detector with tens of cubic kilometers of water-equivalent volume and a large solid angle neutrino acceptance. We review previously reported on the long attenuation length measurements for electric fields in the Hockley salt dome. We consider here several detector geometries and their sensitivities to cosmic neutrino fluxes. We also report on insights yielded by Monte Carlo studies into the scaling laws governing the design of such a detector.

Features of the hadronic interactions of cosmic ray particles that make it difficult to measure their energies and identities precisely also provide tools by which these limitations can be partially overcome, if the detector in question is properly instrumented. I review a growing body of experimental and theoretical work to demonstrate methods by which calorimetry of cosmic rays using thin calorimeters may be optimized, and performance improved, by the use of multiple methods to read out the energy deposited by the developing shower. Examples are given using scintillating fiber, Cherenkov readout of quartz optical fiber, and silicon dE/dx information.

EUSO - Extreme Universe Space Observatory, is a precursor space mission aiming at important scientific objectives with an innovative instrumentation approach. For the first time an attempt will be done to detect Extensive Air Shower from space. EUSO will image the streak of the UV fluorescence light produced from the outer particles interacting with the Earth's atmosphere. The EUSO telescope, constituted by a large Fresnel optics and a finely segmented focal surface detector, will look downward from the ISS (International Space Station) the nocturnal atmosphere of the Earth. The 60 degrees of the optics Field Of View and the 400 km of altitude of the ISS, turn out a very large geometrical factor of the order of half million of km² sr. An appropriate electronics design allows the use of a monocular telescope. The fast time resolution adopted and the single counting technique make possible to reconstruct the shower arrival direction and energy with high precision. EUSO is at the present under an ESA (European Space Agency) phase A evaluation study.

The Extreme Universe Space Observatory (EUSO) is a wide angle refractive telescope in near-ultraviolet wavelength region to detect extremely high energy cosmic rays by observing time-resolved air-fluorescence images of the extensive air showers from the International Space Station. The focal surface detector of the EUSO is designed to be a mosaic of multianode photomultipliers to realize the single photoelectron counting capability. We describe the current status of the conceptual design and the feasibility study of the focal surface of the EUSO telescope.

Optical systems consisting of Fresnel lenses have been shown to provide large aperture, wide field imaging capabilities for systems with forgiving imaging requirements. Fresnel lenses can be manufactured very thin, which makes them ideal for space applications where system mass and absorption losses are critical. A pair of double-sided, curved Fresnel lenses has been proposed as the optical elements for a space-based detector, the Extreme Universe Space Observatory, (EUSO). The EUSO mission objective is to investigate extreme energy cosmic rays (EECRs), those with energies >3E¹⁹ eV, and very high-energy cosmic neutrinos. EUSO will use the earth's atmosphere as a calorimeter by observing atmospheric fluorescence in the Earth's night sky produced by the extensive air showers (EASs) created by EECRs. This paper will describe the EUSO mission and the design of the 2.5-meter optical subsystem. Results of test performed on prototype systems and manufacturing options will also be discussed.

The Extreme Universe Space Observatory (EUSO) is an international program recently approved by ESA for accommodation on the International Space Station. The aim of this telescope is to detect the very rare ultra-high-energy cosmic ray events looking downward the Earth atmosphere from the Space Station. The interaction between these cosmic rays and nitrogen molecules in the atmosphere produces fluorescence radiation in the ultraviolet, in the region ranging from 300 nm up to 400 nm. This radiation is collected by Fresnel lenses onto a focal plane detector composed of about 5000 Multi-Anodes Photomultiplier tubes (MAPMT) providing 2 × 10⁵ 4-mm² pixels. The phase A of this complex program started in March 2002 and it will last one year. During this period the MAPMTs will be fully tested and characterized in the UV region of interest and the focal plane architecture will be designed taking into account the constraints given by the optical design and the results from tests. The test measurements will give information on the response, by changing parameters such as the incidence angle, the gain, the dinode biasing. Ageing effects will be also evaluated. This paper reports on the results of UV measurements on MAPMT obtained at the INFN in Florence, Italy, and it presents the concept study of the UV filter system and the evaluation of a new compact light collector/filter device to be coupled with the detector.

The cosmic ray all-particle spectrum has a small steepening of its spectral slope, or 'knee', near 10¹⁵ eV. Changes in the nuclear composition of cosmic rays may be associated with the knee and provide clues concerning the origin of the spectral change. An ultra-long duration balloon experiment, Cosmic Ray Energetics and Mass (CREAM), is being constructed to measure cosmic ray elemental spectra at energies just below the knee to look for evidence of changes in composition. CREAM employs a thin calorimeter and transition radiation detector to provide multiple measures of the particle energy. A novel technique, the timing charge detector, is used to identify the charge of the incident primary cosmic ray in the presence of the albedo particles generated by interactions in the calorimeter.

The overall cosmic ray intensity spectrum falls as a constant power law over at least 11 decades of particle energy. One of the only features in this spectrum is the slight change in power law index near 10¹⁵ eV, often called the knee of the spectrum. Accurate measurements of cosmic ray elemental abundances into this energy region are expected to reveal the origin of this feature, and possibly the nature of cosmic ray sources. The extremely low intensity of particles at these energies (a few per m² per year) makes the detection challenging. Since only direct measurements have so far proved reliable for the accurate determination of elemental composition, a large-area, light weight, device is needed to achieve long exposures above the atmosphere either on high altitude balloons or spacecraft. Here we report on a detector which uses the x-ray transition radiation yield from plastic foams to provide a response into the knee region for heavy elements. We use individual xenon-filled gas proportional tubes as detectors, combined with Amplex ASIC chip electronics for readout. The construction of this type of detector, and its implementation in the upcoming NASA CREAM 100 day high-altitude balloon payload is described. Also discussed is the calibration of the detector in an accelerator beam at CERN and a comparison with GEANT4 Monet Carlo simulations.

The ANITA project is designed to investigate ultra-high energy (>10¹⁷ eV) cosmic ray interactions throughout the universe by detecting the neutrinos created in those interactions. These high energy neutrinos are detectable through their interactions within the Antarctic ice sheet, which ANITA will use as a detector target that effectively converts the neutrino interactions to radio pulses. This paper will give an overview of the project including scientific objectives, detection description and mission design.

We will report on the details of the ANITA instrument. This instrument is fundamentally a broadband antenna, which is arrayed and constructed in such a way as to be optimized for the detection and characterization of high-energy neutrino cascades. The requirement to maximize the detector view of the Antarctic ice fields implies low gain antennas yet the need for maximum sensitivity dictates using the highest gain possible. Since the Cherenkov signal increases quadratically at higher frequencies suggesting that the optimal selection is an antenna with constant gain as a function of frequency. The baseline design will be a linearly polarized log-periodic zigzag (LPZZ) antenna.

A number of particle astrophysics initiatives to exploit radio emission from high energy particle cascades require high-frequency sampling of antenna array signals. Nyquist-limited sampling of GHz frequency radio signals for an antenna array may be accomplished by commercially available test units. However, these technologies are incompatible with the size, power and cost constraints of long-duration balloon or satellite flight. Taking advantage of low trigger rates for such arrays, high resolution digitization may be performed a postori, at much slower speed and power, on waveforms stored in analog storage cells. This paper presents the design and performance simulation of a multi-channel CMOS VLSI ASIC named STRAW (Self-Triggered Recorder for Analog Waveforms), optimized for low duty-cycle, high sampling frequency operation.

The FORTE satellite records bursts of electromagnetic waves arising from near the Earth's surface in the radio frequency (RF) range of 30 to 300 MHz with a polarization-selective antenna. We investigate possible RF signatures of ultra-high energy cosmic rays (UHECR), including Cherenkov radiation in ice, UHECR-triggered lightning emission, incoherent bremsstrahlung of the ionization trail, and direct geomagnetic synchrotron radiation from the high-energy particles in the shower. The FORTE database consists of over 4 million recorded events to date, and may include a significant number associated with cosmic rays near or beyond the Greisen-Zatsemin-Kuzmin (GZK) cutoff. As a first stage of investigation, we search for FORTE events in the period from September 1997 to December 1999 which can have been produced by Cherenkov VHF radiation from a UHE neutrino shower in the Greenland ice sheet. After application of several background rejection methods, one event is left that requires further investigation.

An optical system consisting of a reflecting mirror with a Schmidt corrector plate is presented as a possible design of a space-based observatory for high energy (up to 10²⁰ eV) cosmic rays, by monitoring the fluorescence showers induced after interaction by cosmic rays with the Earth atmosphere. An instrument of that kind is currently into the evaluation phase as an external payload for the International Space Station. The basic requirements demand a system with large field of view, up to ±30°, and large collecting aperture, ≥2 m diameter, to achieve a sufficient sensitivity and event statistics. Among several possible optical systems for this purpose, the Schmidt camera is the simplest, matching most of the optical technical requirements, with some problem for the obscuration due to the focal plane at such extreme field of view. This paper presents ray-tracing simulations for different designs of large aperture (> 2m) Schmidt cameras with FOV from 40° to 50°, with F/# ≈ 0.7 and ground resolution from 1 to 2 km from a LEO. Better performances are achieved with an aspheric mirror, but performances using of a spherical mirror are acceptable with some compromise in resolution. The overall geometrical transmission ranges from 40% to 78%, according to the selected geometry and FOV. Possible technologies for the construction of the main mirror and all other components, including supporting mechanics will be also discussed.

The next generation of imaging air Cherenkov telescopes (IACT) will aim to lower the energy threshold accessible to earthbound gamma-ray astronomy down to 20-40 GeV. Based on the experience with the design of the MAGIC telescope now being commissioned, we started the design of the next major Cherenkov telescope of 30 meters diameter and with a novel camera of high quantum efficiency hybrid photodetectors (HPDs). In this paper we present the expected performance of such an IACT which will lower the energy threshold down to around 5 GeV, the practical limit at which the secondary particles produce enough Cherenkov photons. We also discuss the challenges arising from the different background (mainly due to the cosmic ray electrons instead of cosmic ray hadrons) at such a low energy threshold and the achievable sensitivity for a single such telescopes.

The accurate determination of the elemental composition of cosmic rays at high energies is expected to provide crucial clues on the origin of these particles. Here we discuss a technique that has become possible through the use of modern ground-based Cherenkov imaging detectors. We combine a measurement of the Cherenkov light produced by the incoming cosmic-ray nucleus in the upper atmosphere with an estimate of the total nucleus energy produced by the extensive air shower initiated when the particle interacts deeper in the atmosphere. The emission regions prior to and after the first nuclear interaction can be separated by an imaging Cherenkov system with sufficient angular and temporal resolution. Monte Carlo simulations indicate a widely space array of 10m diameter imaging Cherenkov detectors should have charge resolution of ΔZ/Z <5% for incident iron nuclei in the region of the "knee" of the cosmic-ray energy spectrum. This technique also has the intriguing possibility to unambiguously discover nuclei heavier than iron at energies above 10¹⁴ eV. We describe a strawman detector design for a future observatory dedicated to high resolution cosmic ray measurements. This observatory can also serve as a wide field of view TeV gamma-ray survey instrument.

We developed the gamma-ray camera for SUBARU infrared-optical telescope, named CheSS (Cherenkov light detecting System on Subaru). The CheSS was designed based on Imaging Atmospheric Cherenkov Technique (IACT) which has been established by detections of high energy gamma-ray sources in the last decade. According to our Monte Carlo simulation, the energy thresholds of the CheSS for the Crab are 30 GeV at zenith angle of 10 degrees, and the expected sensitivity for the unpulsed component can reach ~10σ level and more for pulsed one during 10 hours on-source pointing.

A series of multi-channel transient waveform digitization integrated circuits with up to 5 GHz sample rates and parallel 10-bit digitization has been designed, tested, and fabricated in large quantities. The current CMOS circuit uses four arrays of 128 fast switched capacitors per channel to record four parallel analog transient inputs. Triggering and clocking is provided by a current-mode adjustable asynchronous active delay line that uses look-ahead to generate 128 4-way interleaved clocks without the need for external high-speed clocking. After transient capture, each channel is fed into 128 parallel 10-bit analog to digital converters for fast, channel-parallel digitization, followed by digital readout. The fast triggering and waveform capture, channel-parallel digitization and convenient word-parallel digital readout results in a responsive and low dead-time system. Acquisition sample rates range from ~50 kHz to ~3 GHz. Analog input bandwidth is approximately 350 MHz. Fixed-pattern spatial noise, after on-chip digitization, is equivalent to ~5 mV RMS. Temporal noise is typically equivalent to ~1 mV RMS, for a signal to noise ratio of ~2,500:1, RMS. This integrated circuit, the "Analog Transient Waveform Digitizer," has been successfully used to instrument the AMANDA and KamLAND neutrino physics experiments, and has been selected for use in the IceCube neutrino observatory. Current efforts to improve this technology will yield larger array sizes, sample rates in excess of 10 GHz, analog bandwidth exceeding 1 GHz, higher conversion rates, lower dead-time, greater uniformity and enhanced flexibility and ease of use.

Milagro is a water Cherenkov telescope sensitive to gamma rays with energies above 100 GeV. Unlike air-Cherenkov telescopes, Milagro continuously views the entire overhead sky. This capability makes it well suited to search for transient phenomena such as gamma-ray bursts and to discover new phenomena. I will review the design and construction of Milagro, detail the sensitivity of the instrument, including a discussion of background rejection with Milagro. Recent and ongoing upgrades to the instrument are discussed. The paper concludes with a summary of some recent physics results with Milagro.

This paper briefly describes the principle of operation and science goals of the AMANDA high energy neutrino telescope located at the South Pole, Antarctica. Results from an earlier phase of the telescope, called AMANDA-B10, demonstrate both reliable operation and the broad astrophysical reach of this device, which includes searches for a variety of sources of ultrahigh energy neutrinos: generic point sources, Gamma-Ray Bursts and diffuse sources. The predicted sensitivity and angular resolution of the telescope were confirmed by studies of atmospheric muon and neutrino backgrounds. We also report on the status of the analysis from AMANDA-II, a larger version with far greater capabilities. At this stage of analysis, details of the ice properties and other systematic uncertainties of the AMANDA-II telescope are under study, but we have made progress toward critical science objectives. In particular, we focus on the search for continuous emission from astrophysical point sources and the search for correlated neutrino emission from Gamma Ray Bursts detected by BATSE before decommissioning in May 2000. During the next two years, we expect to exploit the full potential of AMANDA-II with the installation of a new data acquisition system that records full waveforms from the in-ice optical sensors.

We describe the current status of the High Resolution Fly's Eye detector. Event reconstruction and associated systematics for stereo reconstruction are discussed and recent preliminary results on the study of the composition of ultra-high energy cosmic rays by the Xmax method are presented. These results indicate that the composition of cosmic rays becomes predominantly light near 10¹⁹ eV and beyond.

The ANTARES deep-sea neutrino telescope will be located at a depth of 2400 m in the Mediterranean Sea. Deployment of the detector will commence this Autumn and is expected to be completed by the end of 2004. With a surface area of the order of 0.1 km² it will be one of the largest European detectors. The aim of neutrino telescopes is to detect high-energy neutrinos from astrophysical sources whilst also providing information on the early Universe. Successful operation of ANTARES in a deep sea environment constitutes an important milestone towards the ultimate goal of the construction of an underwater neutrino telescope at the cubic-kilometer scale. The sky coverage of astrophysical sources offered by a Mediterranean neutrino telescope is complementary to any similar device at the South Pole. The current status of the project is discussed and the expected performance of the detector is described in the context of the scientific programme of the project which comprises astrophysical studies, dark matter searches and neutrino oscillations.