Strange Effects: The Mystifying History of Neutrino Experiments
What Is a Neutrino?
Neutrinos are tiny, elusive and very common. For every proton or electron in the universe there are at least a billion neutrinos. [continue…]
Beta Decay Puzzle
The tiny particles first came to scientists’ attention in beta decay, a radioactive process discovered at the end of the 19th century in which an atom’s nucleus emits an electron and transforms itself into a different atom. [continue…]
In 1956, physicists studying neutrinos had some fancy new tools at their disposal. In the 25 years since the particles were first postulated, the U.S. had built several nuclear reactors for its atomic weapons program.
Many researchers realized that these reactors, which emitted 300 trillion neutrinos per square inch every second, could be harnessed to detect neutrinos. Though they hardly ever interact with matter, there’s a tiny probability that, given enough material, a neutrino will collide with something. In a process that’s basically the reverse of beta decay, this direct hit will generate gamma radiation. [continue…]
The Solar Puzzle
Astronomers want to detect those neutrinos because they contain important information about processes going on in the sun’s center. In 1964, physicist Ray Davis and astronomer John Bacall built an experiment in the Homestake mine in South Dakota to find these neutrinos. The detector needed to be placed deep underground because cosmic rays hitting the Earth’s atmosphere would interfere with the results. [continue…]
The Atmospheric Puzzle
In the 1980s, scientists were occupied with a problem not related to neutrinos in any way. Some theoreticians suggested that the proton – a stable particle by all accounts – might decay into other, lighter subatomic particles. If this occurred, it would be part of physicists’ long-sought dream: a grand unified theory that merged the electromagnetic, weak and strong forces. [continue…]
A New Neutrino?
In 1993, scientists constructed the Liquid Scintillator Neutrino Detector (LSND) experiment at Los Alamos National Lab. Their aim was to figure out if neutrinos can oscillate from one type to another. (Results from the Homestake and proton decay experiments weren’t yet conclusive.)
LSND remains famous among scientists because it saw a small excess of electron antineutrinos appear seemingly from nowhere. The best explanation for this odd anomaly required completely new physics. [continue…]
Beginning in 2002, scientists began running a new experiment named MiniBooNE at Fermi National Accelerator Laboratory in Illinois. MiniBooNE’s aim was to confirm or deny the controversial LSND results. Their initial results seemed to disprove the LSND anomaly, but further data changed that picture. [continue…]
Image: A physicist sits inside the LSND detector. (Los Alamos National Laboratory)