The universe is full of mysteries, and one of the biggest is the neutrino. These particles are so small that they are nearly impossible to detect. Scientists have been trying to figure out just how tiny they are. Recently, they set a new record for the upper limit of a neutrino's mass: no more than 0. 45 electron volts (eV). To put this into perspective, an electron is about 511, 000 eV. This means neutrinos are incredibly light, almost like they don't exist at all. Trillions of these particles pass through your body every second, but you never feel them. They are so small and interact so weakly with other matter that they go completely unnoticed.

Neutrinos are the only elementary particles whose mass is still unknown. This makes them a big question mark in the Standard Model of particle physics. Figuring out the mass of a neutrino could give scientists a better understanding of the universe's laws. One big question is whether neutrinos get their mass from the Higgs boson, like other particles, or if there's a completely new mechanism at work. This is where the Karlsruhe Tritium Neutrino Experiment, or KATRIN, comes in. KATRIN is a massive, 75-foot-long vacuum chamber shaped like a blimp. Scientists use it to study the radioactive decay of tritium. As tritium decays, it releases electrons and antineutrinos. Even though antineutrinos are impossible to measure directly, scientists can study the energy of the leftover electrons to make guesses about the mass of the neutrinos.

After analyzing data for 259 days, the KATRIN team was able to cut their previous estimate for the neutrino's mass in half. They hope that by the time they analyze a full 1, 000 days of data, they will be able to push that limit even lower, maybe down to 0. 2 eV. Neutrinos still have many secrets to reveal. The KATRIN Collaboration's measurements could open a door to new physics and help scientists understand how the early universe evolved. In February, another team detected the most energetic neutrino ever seen deep in the Mediterranean Sea. This suggests that neutrinos might be emitted by interactions between matter and the cosmic microwave background, the oldest visible light in the universe. If the neutrino mass were around one electronvolt, KATRIN could have found its actual value. But since the particle is so small, a new and improved detector—KATRIN++—may be needed to measure its mass with precision. One thing is for sure: the more scientists learn about neutrinos, the more they realize just how little they know about these tiny giants of the universe.

The Tiny Giants of the Universe

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