They have yet to answer what might sound like a basic question: How much do neutrinos weigh? The answer could be key to understanding the nature of the strange particles and of our universe.
To understand why figuring out the mass of neutrinos is such a challenge, first you must understand that there’s more than one way to picture a neutrino. Knowing this, you might be forgiven for thinking that there are three types of neutrinos: electron neutrinos, muon neutrinos and tau neutrinos. These neutrino types are called the three neutrino mass states. Scientists’ current best tools for figuring out the neutrino mass hierarchy are long-baseline neutrino experiments, most notably one called NOvA. Electron drag.
If the hierarchy is normal, muon neutrinos will be more likely to turn into electron neutrinos, and muon antineutrinos will be less likely to turn into electron antineutrinos.
So if NOvA scientists see that, after traveling through miles of rock and dirt, more muon neutrinos and fewer muon antineutrinos than expected have shifted flavors, it will be a sign the mass hierarchy is normal.