The JUNO detector, a huge sphere full of 20,000 tonnes of transparent organic goop, is detecting antineutrinos produced by two nuclear reactors each located the same distance away. After just 2 months, it measured some things about neutrino masses better than ever before! A paper was just published on this.
We're trying to understand the masses of the 3 neutrinos. A big problem is that most experiments can't detect the actual masses, only fancier things that are easier to measure. So we don't even know which neutrino is the heaviest! JUNO should figure this out, though.
Let me tell you a bit more:
The 3 neutrinos have masses called m₁, m₂ and m₃. Yes, physicists are very creative about naming things.
We know m₁ and m₂ are really close to each other, while m₃ is further away. We also know m₁ < m₂, thanks to neutrinos coming out of the Sun. But we don't know whether m₃ is bigger than both the other masses, or smaller! So right now there are two possibilities:
• Normal ordering: m₁ < m₂ < m₃, so m₃ is the heaviest and sits above the closely-spaced m₁, m₂ pair.
• Inverted ordering: m₃ < m₁ < m₂, so m₃ is the lightest, sitting below the closely-spaced pair.
There's a bit of evidence supporting the normal ordering, which is why it's called the 'normal' ordering. Like I said, physicists are very creative about naming things.
In about 5 years, the JUNO team should know which ordering is the right one! But right now, after just 2 months of taking data, they've just measured m₂² - m₁² more accurately than ever before. So they are happy.
But the whole business of neutrino masses is weirder than I've made it sound.
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