Neutrinos are important elementary particles for our cosmology. However, some basic questions about these particles are still unclear – including their exact mass. Now physicists have managed to further narrow down the upper limit for the Neutrinomasse at the Katrin experiment in Karlsruhe. On the basis of the energies measured by the tritium, they determined that the neutrino has to weigh less than 0.45 electron volts – this is less than a millionth of the mass of an electron. Because this measurement result is independent of assumptions and cosmological models, it helps to further narrow down possible effects of these elementary particles to basic physical processes.
Neutrinos are among the most common and at the same time the most puzzling particle in our universe. Because these non-invited elementary particles hardly have matter with matter, have almost no mass and occur in three varieties: as electron, myon and tau neutrinos. According to the standard model of particle physics, neutrinos should actually be Masselos. But physicists discovered a peculiarity of the neutrinos a long time ago that contradicts this: the elementary particles can literally change their “flavor” in flight and convert into one of the other varieties. From this neutrino oscillation, however, it follows that, contrary to original assumptions, neutrinos must have a mass. “The oscillations identify the flavor states of the neutrinos as overlaps of their mass states,” explains the Katrin collaboration. In other words, each of the three types of neutrinos has a tiny but characteristic mass, from the combination of which the total mass of the particle results.
“Energy Control” reveals the neutrinomass
However, the problem: Because neutrinos hardly interact with matter, their mass cannot be measured directly. However, it works indirectly – among others with the Katrin experiment (Karlsruhe Tritium Neutrino Experiment). In this 70 -meter -long complex, physicists measure the betaer of radioactive tritium. In this decay, an electron and an antineutrino are released. It is known that a total energy of 16,800 electron volt is released. This is distributed proportionally to the two particles. The maximum energy of the electron can therefore be determined which proportion of energy the neutrino has – and according to Einstein’s famous Formula E = MC
Now the physicists of Katrin collaboration have published a new, even more detailed result. It is based on five measurement campaigns that were carried out between March 2019 and June 2021. On the total of 259 measurement days, the team analyzed the energy of around 36 million energetic electrons from the beta of the tritium – six times more than in the last result. In addition, the measurements of technical optimizations of the system benefit, which increases the sensitivity of Katrin for the effective antineutrinomass by a factor of two, as the team reports. At the same time, interference effects and uncertainties could be reduced. This made it possible to further narrow down the upper limit for the neutrinomasse. “Based on our best results, we get an upper limit of M <0.45 electron volt with a confidence interval of 90 percent," the physicists write. The neutrinomass is therefore somewhat lower than previously assumed.
Measurements continue until the end of 2025
However, this is not yet the last word: the Katrin experiment will continue until the end of 2025 and is said to have reached 1,000 measurement days. The final evaluation of these measurements could then include more than five times as many values as the current result. “Based on the current operating conditions, we expect that we can achieve a final sensitivity better than 0.3 electron volts,” write the physicists. This could help to further approach the actual mass of this difficult to fit elementary particles. “If you knew the mass of the neutrinos, you would be able to answer fundamental questions in cosmology, astrophysics and particle physics,” explained Hamish Robertson from the University of Washington of the previous Katrin result. Because these “ghost particles” could play an important role for still unexplained cosmic phenomena – from mysterious imbalance between antimatter and matter to “new physics” beyond the standard model to the still unknown particles of dark matter.
Source: Katrin Collaboration (Karlsruhe), Science, Doi: 10.1126/science.adq9592