So at least we know it's not massless

The neutrino has a mass.

Back when they were first discovered, even that wasn't certain.  But now the scientists are sure it doesn't weigh nearly 2 electron volts (eV);  they're sure it can't weigh more than 1.1 eV.

I'm not a physicist, but I know that isn't very much. By comparison, the mass of a proton (in energy equivalence) is a little over 938 MeV, where "MeV" stands for megaelectronvolt, aka 1 million eV.  So a proton is about 938 million times heavier than a neutrino.

And a proton is not very big!

A new experiment slashes the maximum possible mass of tiny neutrinos

"To make matters more complicated, neutrinos typically don’t have a well-defined mass. Due to the intricacies of quantum mechanics, the particles are made up of three different mass states at once. What KATRIN measures is an “effective mass,” a combination of those three masses."

Oh, what's KATRIN?  It's the device that helped measure the neutrino mass.

And it's very, very, very big.  (Read about how it was shipped from where it was built to where it was installed.)

The silver thing that looks like a grounded zeppelin is KATRIN.