# Why is neutrino research important

## KATRIN instrumentHow much does a neutrino weigh?

Neutrinos are probably the most abundant massive particles in the universe. We also come into constant contact with them, but they just fly through us - probably billions of them every second and probably at the speed of light. Since they hardly show any interaction, it is incredibly difficult to detect them. And the detectors are in complete contrast to the size of the particles. The high-energy neutrino observatory IceCube in the ice of the South Pole is about one cubic kilometer in size.

### Neutrino research in Germany

Neutrino research in Germany, for example, takes place at the Karlsruhe Institute of Technology. The KATRIN experiment is running there - KATRIN for Karlsruhe Tritium Neutrino Collaboration.

Here the researchers are trying to solve one of the neutrinos' riddles. Do neutrinos have a mass? And if so: how heavy is the particle? And now, for the first time, they have an answer to the question.

### 500,000 times lighter than an electron

"We are pleased to be able to inform you of the result of our first neutrino mass measurement," says the KATRIN experiment. And it reads: A neutrino weighs a maximum of 1.1 electron volts.

But why not grams, neither milli nor micro, but electron volts? In particle physics, this is also a common unit of measurement for mass. You can also convert it, but the value is extremely small, it arises when you divide 1 electron volt (eV) by the square of the speed of light - according to Einstein's famous formula E = mc2. And the result is a value of around 1.783 times 10 to the power of minus 36 kilograms - a number with a zero in front of and a lot after the decimal point.

It's pretty unwieldy. That is why the physicists in Karlsruhe chose a different comparison. The mass of the neutrino is 500,000 times less than that of an electron. And so the researchers halved the previously known value of 2 eV.

### Why is that so important?

The researchers hope that by solving the neutrino riddle they can answer many other unanswered questions in physics, such as the big bang and antimatter. That is why 200 researchers from all over Europe and America work at the KATRIN. For their experiments, they are investigating the beta decay of tritium - a radioactive hydrogen isotope that emits an electron and a neutrino. The researchers determined the value that has now been published during a 28-day measurement cycle in early 2019.