- News Home
12 December 2013 1:00 pm ,
Vol. 342 ,
The iconic 125-year-old Lick Observatory on Mount Hamilton near San Jose, California, is facing the threat of closure...
Recent results from the Curiosity Mars rover have helped scientists formulate a plan for the next phase of its mission...
A new, remarkably powerful drug that cripples the hepatitis C virus (HCV) came to market last week, but it sells for $...
In pretoothbrush populations, gumlines would often be marred by a thick, visible crust of calcium phosphate, food...
Evolutionary biologists have long studied how the Mexican tetra, a drab fish that lives in rivers and creeks but has...
Victorian astronomers spent countless hours laboriously charting the positions of stars in the sky. Such sky mapping,...
In an ambitious project to study 1000 years of sickness and health, researchers are excavating the graveyard of the now...
Stefan Behnisch has won awards for designing science labs and other buildings that are smart, sustainable, and...
- 12 December 2013 1:00 pm , Vol. 342 , #6164
- About Us
Elusive Particle Leaves Telltale Trace
21 July 2000 7:00 pm
Nearly massless and incredibly rare, the tau neutrino scorns its surroundings, seldom interacting with more common matter. These properties make it difficult to detect. Now, an international team of physicists has laid claim to the first "direct" detection of the tau neutrino.
Neutrinos were discovered after scientists failed to balance their subatomic books. In the 1930s, Wolfgang Pauli proposed that a very lightweight, weakly interacting particle was carrying away the energy that was missing from radioactive decays. The existence of the neutrino was confirmed a few decades later. Physicists believe there are three types of neutrinos, each named for the fundamental particle it interacts with: The electron neutrino interacts with electrons, the muon neutrino with muons, and the tau neutrino with taus. When physicists have fired beams of electron neutrinos at a target, they produce electrons. Likewise, muon neutrinos shot at a target generate muons. But no one has observed this for tau neutrinos.
At the Direct Observation of the Nu Tau (DONUT) experiment based at the Fermi National Accelerator Laboratory (Fermilab) near Chicago, scientists tried their hand with a 800 giga electron volt proton beam. They created what should be tau neutrinos and shot them through meter-long steel targets. One out of every trillion tau neutrinos interacted with an iron nucleus and created a tau particle, which, in turn, left a telltale track on layers of emulsions that acted like photographic plates. The yield: four taus that the DONUT team is quite confident came from tau neutrinos.
"It was a hard experiment, an expensive experiment, and a somewhat unfashionable experiment," says Stanford University physicist Martin Perl. Physicists already knew that tau neutrinos existed, from missing-energy analysis of tau particles, so some scientists saw no need to perform it at all. Perl disagrees. "It was very, very important to find out," he says. "Not only does it confirm [the tau neutrino's] existence, it shows that it interacts in a more-or-less normal fashion." DONUT team member Regina Rameika agrees. "It's just a relief, really," she says. "It's kind of one of those things you had to do."
DONUT home page