“It’s like changing your identity.” For example, some electron neutrinos from the sun turn into muon and tau neutrinos by the time they reach Earth. “If a neutrino is born as a certain flavor, as it travels, it can morph into other flavors,” explains Gollapinni, who is part of the DUNE collaboration. Neutrinos come in three “flavors”: electron, muon and tau. One of them, dubbed the Deep Underground Neutrino Experiment, or DUNE, aims to understand another mysterious property of neutrinos: how they oscillate, or change type. Researchers are currently developing new experiments to further our understanding of neutrinos. Once the scientists record the total energy from this experiment, it is simply a matter of subtracting out the electron’s energy: whatever is left over belongs to the neutrinos. The maximum energy of these electrons is well documented. Instead the spectrometer measures the energy of electrons that are released alongside neutrinos by radioactive hydrogen as it decays. Valerius, who works on the project, describes it as “a big pizza oven.”Įven this setup can’t detect the elusive ghost particles directly, however. The experiment switches to high temperatures when it needs cleaning. The extreme low temperatures keep highly heat-sensitive supermagnets cold enough to generate a strong magnetic field that allows detectors to catch individual particles. KATRIN’s 200-metric-ton spectrometer and 70 meters of ultra-high-vacuum tubing are capable of reaching temperatures as low as -270.15 degrees Celsius and as high as 250 degrees C, allowing researchers to detect billions of particles. Such a precise measurement requires very sensitive-and very large-equipment. And in early 2022 data from the Karlsruhe Tritium Neutrino Experiment (KATRIN) in Germany. In the mid-2000s the Mainz Neutrino Mass Experiment in Germany had set the upper limit of a neutrino’s mass at 2.3 electron volts. Theory predicted that neutrinos would be completely massless.īut in 2015 Takaaki Kajita of the University of Tokyo and Arthur McDonald of Queen’s University in Ontario won the Nobel Prize in Physics for research that proved the particles do actually have mass-though it did not reveal how much. Pauli’s neutral particle was at last confirmed in 1956 in an experiment that proved its existence-but not its size. So Pauli proposed what he described as a “desperate remedy”: a new type of small, chargeless fundamental particle that was emitted alongside the electrons and accounted for the missing energy. This observation broke the the first law of thermodynamics, which states that energy cannot be created or destroyed. Rather than being emitted as electrons, a small fraction of the decaying atom’s energy had apparently vanished. Over multiple experiments, Pauli’s contemporaries had noticed an accounting error when observing beta decay, a process by which certain radioactive atoms break down. In 1930 renowned physicist Wolfgang Pauli was puzzling over a seemingly impossible conundrum. Theoretical physicists still know remarkably little about neutrinos, despite the fact that they have been aware of their existence for nearly a century. “In your entire lifetime, if one neutrino interacts with you, then you’re lucky,” says experimental particle physicist Sowjanya Gollapinni of Los Alamos National Laboratory. But because of their small size and lack of charge, they rarely interact with your tissues-or anything else. Tens of trillions of neutrinos pass through your body every second, originating mostly from the sun. With a mass of less than 0.8 electron volt each, they are “hundreds of thousands of times lighter than the next lightest particle, which is the electron,” says Kathrin Valerius, an astroparticle researcher at Germany’s Karlsruhe Institute of Technology. New research is bringing science closer than ever to understanding the nature of neutrinos, from their size to their fundamental properties. Sometimes known as “ghost particles,” these mysterious little packets of energy have no electrical charge, have almost no mass and come in at least three distinct varieties. Of all the elementary particles in the universe, neutrinos may be the strangest.
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