Decades-long ghost particle mystery nears answer as physicists close in on neutrino’s weight

KATRIN experiment tightens the search for elusive neutrino mass. (Representative Image: Canva)

Each second, phantom particles that are invisible, unknown, and unruffled go through our body. They are neutrinos, one of the most enigmatic guests in the universe. We still have no idea as basic as their weight, though they number nearly as much as all the particles in the visible universe. But that answer may now be within reach thanks to a lab in Germany. Correcting the mass of the neutrino

Neutrino mass is currently being monitored by researchers at the KATRIN laboratory in Karlsruhe. Their latest study puts the upper limit at 0.45 electron volts (eV). That is very light, over a million times lighter than an electron. Their ongoing 1,000-day test run featured this development, though three-quarters of data remain to be analyzed. The group is aiming to take the limit even lower, down to 0.3 eV, with improved sensitivity, which now is twice that of last year.

Tracking unseen energy changes

Researchers at KATRIN study tritium decay energy for signs of slight disturbances caused by neutrino emission. By offering clues, these slight variations in the energy spectrum allow researchers to estimate the mass of neutrinos. Just over 36 million electron readings have been analyzed so far. While neutrinos themselves cannot be seen, scientists can determine their underlying nature indirectly from energy changes.

A physics rule-breaker: the neutrino
The Standard Model of particle physics insisted that neutrinos were massless for decades. While it is hard to measure their mass, that model has since been disproven. It's hard to keep track of one mass value due to the fact that neutrinos switch between three different "flavours." Nevertheless, the most precise total measurement to date of their combined masses was made by the KATRIN experiment.

One final step prior to further missions
Although KATRIN cannot give a conclusive mass value, its results are crucial to pursuing further study. Due to its cost and complexity, project coordinators believe this will be the last complete-scale effort. The results will pave the way for more advanced neutrino experiments, though. We're closer to understanding these strange, quiet particles that make up our universe, but the search continues.