trace an energy particle

November 26, 2023 5:12 AM

In this article about a rogue high energy particle, one of the researchers says, “You trace its trajectory to its source and there’s nothing high energy enough to have produced it,”. How do they trace something like this to a source?
posted by dhruva to Science & Nature (4 answers total)

Telescope Array Project:

The experiment is designed to observe air showers induced by ultra-high-energy cosmic ray using a combination of ground array and air-fluorescence techniques.

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The Telescope Array observatory is a hybrid detector system consisting of both an array of 507 scintillation surface detectors (SD) which measure the distribution of charged particles at the Earth's surface, and three fluorescence stations which observe the night sky above the SD array.[2] Each fluorescence station is also accompanied by a LIDAR system for atmospheric monitoring.[3] The SD array is much like that of the AGASA group, but covers an area that is nine times larger. The hybrid setup of the Telescope Array project allows for simultaneous observation of both the longitudinal development and the lateral distribution of the air showers. When a cosmic ray passes through the Earth's atmosphere and triggers an air shower, the fluorescence telescopes measure the scintillation light generated as the shower passes through the gas of the atmosphere, while the array of scintillator surface detectors samples the footprint of the shower when it reaches the Earth's surface.

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The Telescope Array has three fluorescence detector (FD) telescope stations. As in the previous Fly's Eye and High Resolution Fly's Eye (HiRes) experiments, these detectors work by measuring the air fluorescence light emitted by an extensive air shower. Each FD telescope consists of a primary mirror (made up of 18 smaller hexagonal mirror segments) and a camera. The cameras are made up of 256 photomultiplier tubes (PMTs) which are sensitive to the ultraviolet light generated by a cosmic ray air shower.[1]

The stations are positioned on a triangle about 35 km apart from one another with the Central Laser Facility close to the triangle's center. Each of the three stations has 12–14 telescopes viewing the range from 3°–33° elevation. The three sites are named Black Rock Mesa (BRM), Long Ridge (LR), and Middle Drum (MD).[5] By combining the data from the three sites, it is possible to determine the primary energy, the arrival direction, and the maximum point of longitudinal development for an air shower.

posted by zamboni at 6:09 AM on November 26, 2023

Best answer: When a high-energy particle like this enters the top of the Earth's atmosphere from space, it barrels through the nuclei of any atoms it happens to run into, producing an "air shower" of atomic fragments in its wake. Those atomic fragments are moving fast enough in the air that they produce Cherenkov radiation, which in turn excites air molecules producing fluorescence that is detected by one portion of the Telescope Array observatory. Meanwhile, a subset of the air-shower particles actually hit the ground, and, if the footprint of the air shower happens to overlap one or more detectors, they also are directly detected.

The "streak of light" in the sky produced by the air shower is imaged by multiple telescopes in the array, which lets one reconstruct its direction in 3 dimensions; the direct information about where the air shower hits the ground gives another data point to refine the reconstruction. (Imagine having several surveillance cameras at several known locations record a meteor track and also knowing where the meteor hit the ground.) Since these super-duper-high-energy particles basically travel in a straight line, once you know the track you can "point back" to the direction in the sky where the particle came from. We don't know how far the particle came, but we can still see whether there's anything obvious in the direction the particle came from, like an active galactic nucleus. In this case, there's no obvious source, which is puzzling (to say the least) for the second-highest-energy cosmic ray ever detected.
posted by heatherlogan at 6:12 AM on November 26, 2023 [14 favorites]

And from the article:

But particles with Oh-My-God or Amaterasu-level energy would be expected to blast through intergalactic space relatively unbent by galactic and extra-galactic magnetic fields, meaning it should be possible to trace their origin.

So the assumption is this went in a straight line.
posted by mark k at 8:01 AM on November 26, 2023 [1 favorite]

The stations are positioned on a triangle about 35 km apart

Simply put, they didn’t just observe it once. There were separate observations from each station. and based on the timing from those they can deduce the line it was traveling.

After that it’s just a matter of looking back along that line to see if there is anything there.
posted by Tell Me No Lies at 8:07 AM on November 26, 2023