Extensive air showers and measurement techniques

A cosmic ray observatory records individual particles using the atmosphere as a transducer and amplifier. Each extremely high energy cosmic ray converts into an air shower that grows to billions of secondary particles. A large cosmic ray observatory senses all such air showers landing in a collection area that spans thousands of square kilometers. Measuring an air shower in detail yields an accurate arrival direction, a good energy estimate, and a likelihood distribution for the mass of the primary cosmic ray. Modern ‘hybrid’ observatories combine a surface array of particle detectors with telescopes that observe radiation produced by the developing shower front as it traverses the atmosphere. To cite this article: P. Sommers, C. R. Physique 5 (2004).