Neutrinos are among the most mysterious and fascinating particles in the universe. These tiny,neutral particles are constantly moving through matter, including our own bodies, withoutleaving a trace. Although they are incredibly abundant, they remain difficult to detect and even

harder to understand. One of the biggest questions surrounding neutrinos is just how much they weigh. Now, a recent breakthrough by scientists working on the Karlsruhe Tritium Neutrino (KATRIN) experiment in Germany has brought us closer to answering that question.

In a paper published in Science on April 11, the KATRIN team announced that the mass of the neutrino is less than 0.45 electron volts (eV). This new finding cuts their previous upper limit nearly in half and sets a new benchmark for precision in measuring neutrino mass. To put that in

perspective, an electron has a mass of about 511,000 eV, which means neutrinos are more than a million times lighter. Despite their small size, neutrinos play an outsized role in shaping both the

universe and the future of particle physics.

Understanding the mass of neutrinos is a critical step in modern physics. For decades, scientists believed neutrinos were massless, as predicted by the Standard Model, the leading theory that explains how particles behave. However, the discovery that neutrinos can change between

different types, or “flavors,” proved they must have some mass. This challenged the completeness of the Standard Model and opened the door to new theories that go beyond our

current understanding of the universe. Measuring the neutrino’s mass more precisely could help scientists uncover these deeper laws of nature.

The KATRIN experiment works by studying a rare type of hydrogen called tritium. When tritium decays, it emits an electron and an electron antineutrino. The energy of the electron is slightly reduced if the neutrino has mass. By measuring the energies of more than 36 million electrons, the KATRIN team could detect this tiny difference and use it to set a tighter limit on the neutrino’s mass. This method offers a direct and model-independent approach that avoids the uncertainties associated with calculations based on cosmological models.

Although other scientists have tried to estimate neutrino mass using observations from space, such as the structure of galaxies or the cosmic microwave background, these methods rely on assumptions about how the universe evolved. KATRIN, in contrast, provides laboratory-based

results that are grounded in measurable data. This makes its findings especially reliable and valuable to the field of particle physics.

While the exact mass of the neutrino is still unknown, KATRIN has taken us a significant step closer to discovering it. The experiment will continue collecting data until the end of 2025, with much more information still waiting to be analyzed. As this work continues, it promises to

deepen our understanding not only of neutrinos themselves but also of the universe and the fundamental rules that govern it.