Antineutrinos are distinguished from neutrinos by having opposite-signed lepton number and weak isospin, and right-handed instead of left-handed chirality. įor each neutrino, there also exists a corresponding antiparticle, called an antineutrino, which also has spin of 1 / 2 and no electric charge. The three mass values are not yet known as of 2024, but laboratory experiments and cosmological observations have determined the differences of their squares, an upper limit on their sum (< 2.14 ×10 −37 kg), and an upper limit on the mass of the electron neutrino. For example, an electron neutrino produced in a beta decay reaction may interact in a distant detector as a muon or tau neutrino. Similar to some other neutral particles, neutrinos oscillate between different flavors in flight as a consequence. Although neutrinos were long believed to be massless, it is now known that there are three discrete neutrino masses with different tiny values (the smallest of which could even be zero ), but the three masses do not uniquely correspond to the three flavors: A neutrino created with a specific flavor is a specific mixture of all three mass states (a quantum superposition). Weak interactions create neutrinos in one of three leptonic flavors:Įach flavor is associated with the correspondingly named charged lepton. Thus, neutrinos typically pass through normal matter unimpeded and undetected. The weak force has a very short range, the gravitational interaction is extremely weak due to the very small mass of the neutrino, and neutrinos do not participate in the electromagnetic interaction or the strong interaction. The rest mass of the neutrino is much smaller than that of the other known elementary particles (excluding massless particles). The neutrino is so named because it is electrically neutral and because its rest mass is so small ( -ino) that it was long thought to be zero. < 0.120 eV ( < 2.14 × 10 −37 kg), 95% confidence level, sum of 3 "flavours" Ī neutrino ( / nj uː ˈ t r iː n oʊ/ new- TREE-noh denoted by the Greek letter ν) is a fermion (an elementary particle with spin of 1 / 2) that interacts only via the weak interaction and gravity. Some are antimatter versions.Μ: Leon Lederman, Melvin Schwartz and Jack Steinberger (1962) They come in different types and can be thought of in terms of flavors, masses, and energies. Physicist Enrico Fermi popularized the name “neutrino”, which is Italian for “little neutral one.” Neutrinos are denoted by the Greek symbol ν, or nu (pronounced “new”). To increase the odds of seeing them, scientists build huge detectors and create intense sources of neutrinos. Most neutrinos will pass through Earth without interacting at all. This weak force is important only at very short distances, which means tiny neutrinos can skirt through the atoms of massive objects without interacting. The only ways they interact is through gravity and the weak force, which is, well, weak. While we keep learning more about neutrinos, with new answers come new mysteries. First predicted in 1930, they weren’t discovered in experiments until 1956, and scientists thought they were massless until even later. These little particles have an interesting history. Neutrinos come from all kinds of different sources and are often the product of heavy particles turning into lighter ones, a process called “decay.” They’re also extremely common-in fact, they’re the most abundant massive particle in the universe. They are the lightest of all the subatomic particles that have mass. Neutrinos are also incredibly small and light. But while electrons have a negative charge, neutrinos have no charge at all. Neutrinos are members of the same group as the most famous fundamental particle, the electron (which is powering the device you’re reading this on right now). A neutrino is a particle! It’s one of the so-called fundamental particles, which means it isn’t made of any smaller pieces, at least that we know of.
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