Neutrino
An elusive elementary particle that rarely interacts with matter.
A neutrino (new-TREE-noh; denoted by the Greek letter ν) is an elementary particle that interacts via the weak interaction and gravity. It is electrically neutral and has a rest mass much smaller than that of other known elementary particles (excluding massless particles). Neutrinos typically pass through normal matter unimpeded and with no detectable effect, making them extremely difficult to study.
- type
- Elementary particle
- interaction
- Weak interaction and gravity
- spin
- 1/2 ħ
- flavors
- Electron neutrino, muon neutrino, tau neutrino
- antiparticle
- Antineutrino
Lore & Background
In 1962, Leon M. Lederman, Melvin Schwartz, and Jack Steinberger showed that more than one type of neutrino exists by detecting interactions of the muon neutrino. The tau neutrino was first detected in 2000 by the DONUT collaboration at Fermilab. The solar neutrino problem, a discrepancy between measured and predicted solar neutrino fluxes, was resolved by realizing that neutrinos oscillate between flavors, implying they have nonzero mass.
Reader's Guide
Neutrinos are fundamental to understanding particle physics and the universe. Their extremely weak interactions allow them to pass through vast amounts of matter, making them unique probes of processes otherwise hidden, such as nuclear reactions in the Sun's core and the interior of the Earth. The discovery that neutrinos oscillate between flavors—meaning they have mass—was a major breakthrough, contradicting earlier assumptions and opening new questions about the nature of mass and the Standard Model. Neutrinos are produced in various radioactive decays, including beta decay, nuclear reactions in stars, supernovas, and particle accelerators. The majority of neutrinos detected on Earth come from the Sun, with a flux of about 65 billion per second per square centimeter. Their study continues to challenge and refine our understanding of fundamental physics, with ongoing experiments seeking to determine the exact values of their masses and to explore their role in cosmology.
Did You Know?
- Neutrinos are fermions with spin 1/2 ħ and have no electric charge.
- The name 'neutrino' was jokingly coined by Edoardo Amaldi during a conversation with Enrico Fermi.
- The first detection of a neutrino in nature was in 1965 in a gold mine near Boksburg, South Africa.
- Neutrinos oscillate between different flavors in flight, so an electron neutrino may later interact as a muon or tau neutrino.
Frequently Asked Questions
What is a neutrino?
A neutrino is a fundamental, electrically neutral particle that only feels the weak nuclear force and gravity. It is one of the lightest known elementary particles and carries a spin of 1/2 ħ.
Why are neutrinos so notoriously hard to detect?
Because they interact with ordinary matter almost exclusively through the weak force, they can stream through light-years of lead without a single collision. This near-total transparency means detectors must be enormous and buried deep underground to catch even a handful of events.
What flavors of neutrino exist?
There are three known flavors: the electron neutrino, the muon neutrino, and the tau neutrino, each associated with a corresponding charged lepton. They can oscillate between flavors as they travel, a phenomenon that was key evidence they carry mass.
What is an antineutrino and how does it differ from a neutrino?
An antineutrino is the antiparticle counterpart of a neutrino, commonly produced in nuclear beta decay and in the cores of stars. It shares the same mass and spin as its neutrino partner but carries the opposite lepton number, making it distinguishable in weak-interaction reactions.
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