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14 May 2012

Neutrino, an Elusive Particle

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Neutrinos are one of the fundamental particles which make up the universe.

They are similar to the more familiar electron, with one crucial difference: neutrinos do not carry electric charge. Because neutrinos are electrically neutral, they are not affected by the electromagnetic forces which act on electrons. Neutrinos are affected only by a “weak” sub-atomic force of much shorter range than electromagnetism, and are therefore able to pass through great distances in matter without being affected by it. If neutrinos have mass, they also interact gravitationally with other massive particles, but gravity is by far the weakest of the four known forces.

Particle physicists originally believed that neutrinos were massless. But in the 1990s, a team of Japanese scientists discovered that they actually have a smidgen of mass. This tiny bit of mass may explain why the universe is made up of matter, not antimatter. Early in the process of the Big Bang, there were equal amounts of matter and antimatter, but as the universe expanded and cooled, matter and antimatter were mostly annihilated. And a slight asymmetry favored matter over antimatter. Neutrinos may have something to do with that process.

Studying neutrinos is difficult. They’re tough to detect since they interact so weakly with other particles. But the newly-completed IceCube Neutrino Observatory will study neutrinos inside a cubic kilometer block of ice in Antarctica. Here’s how: when the neutrinos interact with atoms inside the deep arctic ice detectors, they sometimes give off puffs of energy.

The world after the revolution: physics in the second half of the twentieth century, José Manuel Sánchez Ron



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