A proposal for a neutrino detection array over 200,000 sq. kilometers

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Sometimes the acronym for a project goes particularly well in astronomy. This would be absolutely the case for the Giant Radio Array for Neutrino Detection, which wants to scale to a size of 200,000 km² to measure ultra-high-energy tau neutrinos. Is it ambitious? Yes, but that doesn't really prevent humanity from exploring when it wants.

The project is an idea of ​​the GRAND Collaboration hosted by the CNRS, Frances & # 39; Center for Scientific Research. The collaboration has already conducted a few workshops and developed a roadmap to achieve its really ambitious scope. To understand the roadmap, it is helpful first to understand what the project is looking for.

GRAND will search for so-called ultra-high-energy neutrinos. These neutrinos play a large role in the Standard Model of particle physics, but have so far eluded detection at the energy levels at which they are mainly predicted. They can come from two sources. The first comes directly from ultra high energy cosmic rays (UHE), while the second from cosmic UHE rays interacts with the cosmic microwave background that pervades the universe.

A video describing some of the most energetic cosmic rays ever discovered that could be a source of the neutrinos that GRAND will be looking for.
Photo credit: Youtube channel revealed

The specific type of neutrino that GRAND is looking for is called a tau neutrino. This is not a direct result of the neutrino formation events described above, but rather a subsequent form of the muon and electron type neutrinos that generate these events. As such, some of these particles would “swing” into tau neutrinos.

The reason tau neutrinos are of interest is because they have a "just right" chance of being discovered. Essentially, the project scientists would rely on the relatively high probability that UHE neutrinos would interact with ordinary matter. Of the three types of cosmic neutrino UHE rays, the electron simply gets stuck in any ordinary matter with which it interacts, while the muon continues to travel through ordinary matter even as it interacts with it. The “sweet spot” of detection is the tau neutrino, which interacts with regular matter and decays within about 50 km of where it interacts with normal matter.

Video that describes how types of neutrinos vibrate among each other.
Photo credit: MinutePhysics Youtube Channel

The GRAND telescope can absorb this decay and is used specifically for it. The term for the decay of such a tau neutrino is called an "air shower", during which the tau neutrino can then be detected. But first it has to interact with some form of normal matter, and what better mass or normal matter do we have than the earth itself.

The idea of ​​using the earth to create an “air shower” from dew neutrinos is not new, but setting up numerous arrays in mountainous terrain to consistently detect this decay is the basis of what the GRAND Collaboration is with tried her telescope. They are trying to catch the decay of tau neutrinos that are a few kilometers from the earth's crust and that decay in the atmosphere rather than deep underground.

Paper graphic describing GRAND showing the different types of neutrinos and how the “air shower” is used to identify them.
Photo credit: Sijbrand de Jong / GRAND Collaboration

The array uses many specially designed devices to perform this detection. In particular, there would be 200,000 specially designed pieces of equipment for the finished array.

This does not mean that the project will cover an area of ​​200,000 km² (three times the size of the Czech Republic, where a virtual meeting was recently held) for device detection. You would simply need a single detection station per square kilometer.

Imagine a prototype of a data collector and transceiver for the GRAND system
Photo credit: Sijbrand de Jong / GRAND Collaboration

Each detection station consists of a specially designed antenna, an amplifier, and some associated data acquisition hardware. The project team developed an early prototype, but indicates that there is still a long way to go in terms of cost and resilience before the prototype can be fully deployed in 200,000 locations.

This is where the roadmap that the collaboration worked on comes into play. The team has already received around 160,000 euros and completed a set of 35 connected prototypes. In 2020 they started a prototype program called GRANDProto300 with funding of € 1.6 to cover an area of ​​300 km² in the prototype kit. Over the next 5 to 10 years, they hope to bring the cost of a full antenna and data acquisition system down to around $ 500. This price point would enable the full implementation of the entire project with 20 hotspots, each with an antenna for 10,000 km each, for a total price of EUR 200 million.

Grand roadmap with detailed plans for the project for the next 10+ years.
Photo credit: Sijbrand de Jong / GRAND Collaboration

The GRAND project is certainly ambitious, but it could answer some very interesting questions about the Standard Model. The team even points out that if they did not discover any of these decaying tau neutrinos, that would be a revolutionary finding in itself for the Standard Model and would cause a rethink in how these neutrinos work.

More interestingly, if you are interested in pushing the boundaries of experimental particle physics, the team is looking for new additions and would appreciate the additional help in achieving their bold goal. Last but not least, new hires can rest assured that they are working with a team that knows how to brand astronomy projects.

Learn more:

arXiv: Giant radio array for neutrino detection (GRAND)
CNRS: Great collaboration
UT: Neutrinos were detected with such high energy that the Standard Model cannot explain them

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