The universe is big and made up of many different things, none more common than neutrinos. In fact, in just the time it took you read that first line, billions (or more) of them have passed right through you.

Don’t worry, they are so small that they can pass through you (or almost anything else) without causing any trouble at all. But how small are they? This is an important question in physics. Well, more accurately, how light are they, or how much mass do they really have.

When neutrinos were first discovered, it was assumed that they had no mass at all. In fact, the standard model of particle physics, which is the theory that is used for most modern physics assumed that neutrinos had no mass. Since it was discovered that they do indeed have mass (no matter how little), researchers have had to make some adjustments to the theory, but since they do not know how much mass they have, the adjustments are not as accurate as they could be.

So, researchers with the KATRIN collaboration have been working on ‘weighing’ neutrinos to get an answer to his important question. Previously, they ran an experiment for 259 days and analyzed about 36 million electrons from neutrinos. The process of determining the mass of neutrinos is difficult and (so far at least) can’t be done directly. The experiment instead has to start out with tritium, which is a heavier version of hydrogen that has one electron, one proton, and two neutrons (rather than just one electron and one proton).

When Tritium decays into helium-3, it turns one neutron into a proton and one electron is released into an antineutrino (it has the same mass as a neutrino, but with the opposite spin). During this transformation, energy is released and taken away by the antineutrino and the electron. Measuring that tiny bit of energy gives researchers the data they need to measure the mass of a neutrino (hey, nobody ever said science was easy).

To do this, KATRIN takes particles and has them travel around a 70-meter (230-foot) structure. They measure the energy of the electrons using a massive 200-tonne spectrometer. To get an accurate measurement, this needs to be done lots of times (36 million in the previous experiment).

Unfortunately, measuring 36 million electrons over the course of 259 days just wasn’t good enough. So, the team ran another experiment that is still ongoing. This experiment will run for 1000 days and collect data from 250 million electrons. A paper about this experiment has been published in the journal Science and shows that the information they gathered will dramatically reduce the possible range of mass of a neutrino.

According to a comment by Loredana Gastaldo:

“The neutrino mass measuring campaign of the KATRIN experiment will end in 2025 after reaching 1,000 days of data acquisition. Analysis of the full data set gained from this grand project will allow for estimating the effective electron neutrino mass close to the projected value of 0.3 eV at 90% confidence level.”

What does that mean? They will have limited the upper mass range to less than .45 electron volts. That is comparing the mass of a neutrino to that of an electron. A similar comparison that is easier to understand would be if you took something that has 1 gram of mass and compared it to something that has the mass of 40,000 of our Sun’s.

Once all the data is collected and the numbers analyzed, scientists will have a much more accurate range to work with, which can help them in all areas of particle physics. This can also help to further revise (or even replace) the standard model of particle physics. So yeah, it’s kind of a big deal.

Who knew something so small could have such a big impact.

If you thought that was interesting, you might like to read about a quantum computer simulation that has “reversed time” and physics may never be the same.