The subatomic particles called neutrinos are among the most elusive in the particle kingdom. Scientists have
built detectors underground, underwater, and at the South Pole to measure these ghostly particles
that come from the sun, from supernovae and from many other celestial objects. Neutrinos fill the
whole universe, with about 10 million of them per cubic foot, and most of them zip straight through the earth,
and through particle detectors, without leaving a trace. Because they almost never interact with matter,
only sophisticated experiments can catch and measure the properties of neutrinos.
The MINOS Detector, 800 meters underground in Minnesota's Soudan Mine.
In addition to measuring neutrinos from the sky, physicists on earth use powerful accelerators to produce neutrino beams
containing billions of neutrinos, of which a tiny fraction can be measured by detectors placed in the beam line. At
Fermilab, the DONUT accelerator-based neutrino experiment led in 2000 to the discovery of the
tau neutrino, the third of the three known types of neutrinos.
Fermilab is home to two new experiments using neutrino beams, MiniBooNE and MINOS. Both experiments search for neutrino
oscillations, the transformation of one type of neutrino into another. Results from several experiments, including
SuperKamiokande and the Sudbury Neutrino Observatory, have indicated that neutrinos have a very tiny mass. Investigating
neutrino oscillations will shed more light on the phenomena of neutrino mass and the neutrino mixing process.
The MiniBooNE experiment investigates the question of neutrino mass by looking for oscillations of muon neutrinos
into electron neutrinos. It uses a large
tank filled with 800 tons of mineral oil to look for particles produced when a neutrino hits the nucleus of
an atom. The signature
of such an interaction is a cone of light that hits some of the 1,520 light-sensitive devices mounted inside the tank.
The first beam-induced neutrino events were observed in September of 2002, and the experiment is currently taking data.
The primary goal of MiniBooNE is to investigate a signal reported by the LSND experiment conducted at Los Alamos
If the MiniBooNE experiment confirms the LSND measurement, the current model for understanding the universe will have
to be changed to take into account a fourth type of neutrino, in addition
to the three currently observed.
Bonnie Fleming from Yale University stands inside the MiniBooNE detector.
The Cerenkov light cone (Video, 5 min.)
The Main Injector Neutrino Oscillation Search, or MINOS, will look for oscillations of muon neutrinos into tau
neutrinos. Fermilab's Neutrinos at the Main Injector project has built the facilities necessary to turn a beam
of protons from the Main Injector into a beam of muon neutrinos. The neutrinos will first pass through
the thousand-ton MINOS Near Detector at Fermilab, where a small fraction of them will be detected. The beam will then travel
450 miles through the earth to a detector 800 meters underground in an old iron mine in
Soudan, Minnesota, where a few neutrinos will leave traces
in the 6,000 ton MINOS Far Detector. The Far Detector in Soudan was completed in July 2003, and the Near Detector
was completed in August 2004. The first beam of neutrinos will be sent from Fermilab to Minnesota in early 2005.
Fermilab theorists are also active in many aspects of studying neutrinos,
from making predictions for what experiments will measure to trying to
understand what new experimental results tell us. One important area of
research concerns the neutrino masses--how they can be measured, why
they are so much smaller than those of other particles, and how
the masses of the different types of neutrinos compare. Another area involves
using neutrinos to study astrophysical sources such as the sun or supernovae,
or studying their impact on cosmology, such as their role in revealing the matter-antimatter asymmetry of
Physicists have observed three different types of neutrinos, but know little about their masses.
Neutrinos matter (PDF, 24 pages)
What's a neutrino?
Neutrinos and their history
Theoretical Physics Department
Theoretical Astrophysics Group