John Linsley

The atmospheric nightglow in the 300–400 nm wavelength: Results by the balloon-borne experiment “BABY”

Abstract The balloon-borne experiment, named BAckground BYpass (BABY) belongs to a wider program that has as its final goal the detection and study of high-energy cosmic rays from space (satellite, Space Station). An information of fundamental importance for this class of projects concerns the nighttime background light. The instrument designed to detect fluorescence photons is basically composed of two collimated photomultipliers: a single photon-counting PMT and a charge integration PMT. We briefly report the details of the design, operation and performance of the detector, which was designed and completely built at the IFCAI–CNR Institute in Palermo. Preliminary analysis and results of the nocturnal background in the range of 300– 400 nm are presented for the whole duration of the flight during the 1998 Mediterranean balloon flight campaign. A substantial part of the flight was at night over the sea.

Very High Energy Cosmic Rays

Results from ground level and underground experiments on cosmic rays with energy 1012to 1020eV are reviewed. They show that the energy spectrum has two significant features, a ‘knee’ and an ‘ankle’. The arrival directions of these cosmic rays at the solar system are anisotropic, features of the anisotropy appearing to be correlated with features of the spectrum. Detailed interpretation of this information awaits conclusive evidence regarding the composition of these cosmic rays. New results and prospective new results on the composition are described and discussed.

Erratum to: Proton-proton total cross-section atEc.m. = 15 to 150 TeV from cosmic-ray data

SummaryData on the fluctuation in depth of maximum development of cosmicray air showers with laboratory energies in the range (105/107) TeV are found to be inconsistent with a In2s energy dependence of σpp, when that quantity is derived from σpa with a geometrical scaling model by means of Glauber theory. The data agree remarkably well with the Block-Cahn best-fit extrapolation of ISR results.

Search for the end of the cosmic ray energy spectrum

The title I was asked to speak about expresses an idea that occurred rather recently in the history of cosmic ray studies. I argue that the idea of a possible end of the cosmic ray energy spectrum came into being after a sequence of three rapid advances in knowledge which I describe, calling them ‘breakthroughs.’ I suggest that the present workshop be regarded as a step toward a fourth breakthrough. I argue that this may occur through application of the Space Airwatch concept—the earth atmosphere as target and signal generator—as embodied in the NASA OWL project.

AIR WATCH: a space mission to observe the UV fluorescence induced in the Earth atmosphere by extreme-energy cosmic radiation

One of the most challenging tissues in Astroparticle Physics is represented today by the observation of the energy spectrum of the Extreme Energy Cosmic Radiation. The very existence of particles with energy above 1020 eV and of neutrinos of comparable energy raises fundamental scientific questions in connection with their origin and propagation in the interstellar/intergalactic space. These particles can be detected through the gain showers produced in the Earth Atmosphere. The shower development is accompanied by emission of fluorescence in the atmosphere, in particular that induced in Nitrogen with characteristics spectral lines in the UV. Following a first suggestion by J. Linsley in the early 1980s, taken over by Y/ Takahashi, the fluorescence observation can be advantageously carried out by space. By using wide angel optics with large collecting surface, we can monitor a target area of atmosphere of the order of millions square kilometers x sr and corresponding mass above 1013 tons, allowing the detection of the very small flux values typical of the EECR and making possible the search of the elusive high energy neutrinos. AIRWATCH follows this approach. We describe the main scientific goals for the investigation of the EECR, High Energy neutrinos and of the Gamma Ray Bursts, together with the relevant connections to the problem of their origin. The experimental framework is outlined and a description is given of the space mission and of the observational strategy.

In What Sense is the Energy Spectrum a Universal Property of Extreme Energy Cosmic Rays

I examine the question, whether at highest energies the cosmic ray energy spectrum may be ‘universall, as the 2.7K microwave background is thought to be. If so, then the GZK cutoff will be a dominant and potentially useful feature. I argue that the present failure to observe this cutoff is explained by defects in the assumptions made by GZK and their followers, who have over-estimated the flux received from many ‘distant’ sources, compared to that from a few ‘local’ sources. I suggest a methodological approach for separating distant and local source contributions, when improved data are made available by the Pierre Auger ground observatories, and by observations from space by means of EUSO and its successor spacecraft.

Atmospheric Background Measurement in the 300–400 nm Band with a Balloon Borne Experiment during a Nocturnal Flight

The balloon borne experiment, named BABY (BAckground BYpass)belongs to a wider program, AIRWATCH-OWL, intended for theobservation of high energy Cosmic Rays from space, detecting thefaint UV fluorescence light emitted by the atmospheric Nitrogen asfinal result of a complex hadronic cascade. In this framework, oneof the fundamental information concern the knowledge of thebackground level. This is one of the main parameters thatcontribute to the sensitivity of any kind of instrument. Theapparatus used for the BABY experiment was designed and completelybuilt at the IFCAI-CNR in Palermo. The instrument is composed bytwo filtered and collimated photomultipliers (PMT) that detect theUV light in the 300–400 nm wavelength. We report a briefdescription of the design of the detector and the results comingfrom a preliminary analysis of the data taken during a nocturnalover-sea observation.

Maximum-energy Auger-shower satellite (MASS/AIRWATCH)

A concept for observation from space of the highest energy cosmic rays above 1020 eV with a satellite-borne observatory has been considered. A maximum-energy auger (air)-shower satellite (MASS) would use segmented lenses (and/or mirrors) and an array of imaging devices (about 106 pixels) to detect and record fluorescent light profiles of cosmic ray cascades in the atmosphere. The field-of-view of MASS could be extended to about (1000 km)2 so that more than 103 events per year could be observed above 1020 eV. From far above the atmosphere, MASS would be capable of observing events at all angles including near horizontal tracks, and would have considerable aperture for high energy photon and neutrino observation. With a large aperture and the spatial and temporal resolution, MASS could determine the energy spectrum, the mass composition, and arrival anisotropy of cosmic rays from 1020 eV to 1022 eV, a region hitherto not explored by ground-based detectors such as the flys eye and air-shower arrays. MASSs ability to identify comic neutrinos and gamma rays may help providing evidence for the theory which attributes the above cut-off cosmic ray flux to the decay of topological defects.