D17 Detection of Particles and Neutrinos

Topic

Cosmic particle detectors extend astronomy into the aforementioned multi-messenger domain, but they do so by detecting particles rather than photons.

A vast volume of a natural transparent medium—such as ice or water—instrumented with light sensors detects the flash of Cherenkov radiation emitted by a secondary particle. This particle is produced when a neutrino interacts with the medium and travels through it faster than light itself; the angle at which the flash is emitted is determined precisely by the optical properties of the medium.

Meanwhile, ground-based arrays covering enormous areas detect the shower of secondary particles produced when high-energy cosmic rays strike Earth's upper atmosphere.

Large underground detectors filled with ultrapure water captured neutrinos from a nearby supernova simultaneously with its visible light for the first time; these same detectors also demonstrated that neutrinos oscillate between different types during their journey—implying that they possess mass, contrary to previous assumptions. Thus, from the expansion of astronomy into the particle domain—with which this document began—to the discovery of neutrino mass—with which it concludes—and encompassing Cherenkov radiation and secondary particle showers, cosmic particle detectors ensure that these almost ghostly messengers, which barely interact with the matter they traverse, still leave a measurable trace in their wake.

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