The way to make a neutrino beam involves not only colliding protons into a fixed target, but collimating the debris and giving the secondary pions and muons enough room to decay into neutrinos before they encounter the solid Earth. (Credit: Reidar Hahn, Fermilab)

Ask Ethan: How can physicists make neutrino beams?

The neutrino is the most ghostly, rarely-interacting particle in all the Standard Model. How well can we truly make “beams” out of them?

The neutrino, of all the fundamental particles presently known to humanity, remains in many ways the most difficult particle of all to detect. For any other particle, once you create it, you can easily detect its presence by building a variety of experimental devices — like pixel detectors, calorimeters, and magnetic fields that bend charged particles — that either detect the passage of those particles directly or detect the tracks left by the original particle’s decay products. Only the neutrino and antineutrino require something extra, as each individual particle needs something like a light-year’s worth of lead to have a 50/50 shot of interacting with it.

So how, then, do particle physics experiments that involve neutrino beams actually work? The upcoming Deep Underground Neutrino Experiment (DUNE) experiment requires one, and yet, it can’t work the way that other particle beams work. That’s what David Yager wants to know, asking:

“How efficient will the DUNE experiment be at directing neutrinos at the far target? […] I live near a nuclear power plant, and I have been told that…