The Story of the Neutrino
Wolfgang Pauli, who proposed the
existence of the neutrino in 1930. |
Its own inventor
doubted if anyone would ever see it. Two thirds of a century ago, physicist
Wolfgang Pauli postulated a new particle to explain the apparent
nonconservation of energy in radioactive decays. But the theoretical particle
he described had properties that made it so elusive that even Pauli wondered
whether anyone would ever observe it. And yet today, not only have scientists
observed neutrinos, but researchers can carry out detailed experiments
involving millions of neutrino events.
Past neutrino
experiments have helped establish the validity of the Standard Model of
particle physics, the theoretical framework that provides our best explanation
of the basic properties of matter. Future neutrino experiments promise not only
to tell us more about the nature of the neutrino itself, but also to illuminate
the path toward new physics beyond the Standard Model.
Wolfgang Pauli |
1930
In a letter to the attendees of a physics conference in
Tübingen, Germany, Wolfgang Pauli proposes as a "desperate remedy" the
existence of a new neutral particle to explain the apparent energy
nonconservation in radioactive decays. During the next few years, scientists
elaborate Pauli's theory and conclude that the new particle must be very weakly
interacting and extremely light. |
1933
Enrico Fermi proposes "neutrino" as the name for Pauli's
postulated particle. He formulates a quantitative theory of weak particle
interactions in which the neutrino plays an integral part.
View
Letter from Enrico Fermi |
Enrico Fermi |
Frederick Reines |
1956
Two American scientists, Frederick Reines and Clyde Cowan,
report the first evidence for neutrinos. They use a fission reactor as a source
of neutrinos and a well-shielded scintillator detector nearby to detect
them. |
1957
An Italian physicist, Bruno Pontecorvo, living in the
USSR, formulates a theory of neutrino "oscillations." He shows that if
different species of neutrinos exist, they might be able to oscillate back and
forth between different species. |
1958
Maurice Goldhaber, Lee Grodzins, and Andrew Sunyar at
Brookhaven National Laboratory demonstrate that the new neutrino has lefthanded
helicity, meaning that it spins along the direction of its motion in the sense
of a lefthanded screw. The experiment helps to distinguish among different
forms of weak interactions. |
1962
A group of scientists from Columbia University and
Brookhaven National Laboratory perform the first accelerator neutrino
experiment and demonstrate the existence of two species of neutrinos, the
electron neutrino,
 , and the muon neutrino,
 .
In 1987, Jack Steinberger, Leon Lederman, and Mel Schwartz win the Nobel Prize
for this discovery. |
J. Steinberger, K. Goulianos, J.
Gaillard, N. Mistry,
G. Danby, W. Hayes, L. Lederman, M. Schwartz |
1968
An experiment deep underground in the Homestake mine in
South Dakota makes the first observation of neutrinos from the sun. But
experimenters see far fewer neutrinos than solar models had predicted.
|
A neutral current event observed in the
Gargamelle bubble chamber at CERN |
1973
An international team working at CERN, the European
Laboratory for Particle Physics, in Geneva, Switzerland, uses a bubble chamber
to observe the first example of a "neutral current" event. Observation of this
new interaction lends strong support to a unified theory of weak and
electromagnetic interactions proposed a few years earlier by Sheldon Glashow,
Abdus Salam, and Steven Weinberg. Shortly afterward, scientists at Fermilab
confirm the discovery. |
1975
A new lepton, tau, is discovered by a group led by
physicist Martin Perl at the Stanford Linear Accelerator Center. Experiments
performed shortly afterward provide strong evidence that there also exists a
third species of neutrino, the tau neutrino,
 .
In 1995, Perl and Reines win the Nobel Prize for their discoveries. |
Stanford Linear
Accelerator
Center |
1987
Large underground water detectors in the Kamioka mine in
Japan and in the Morton salt mine in the U.S. detect the first neutrinos from a
supernova, SN1987A. |
Super Kamiokande experiment |
1998
At the Neutrino '98 conference in Japan, physicists from
the Super-Kamiokande experiment present significant new data on the deficit in
muon neutrinos produced in the Earth's atmosphere. The data suggest that the
deficit varies depending on the distance the neutrinos travel—an
indication that neutrinos oscillate and have mass. |
1999
The Main Injector at Fermilab begins operation. The
combination of its high-intensity particle beam and an energy of 120 GeV allows
a new generation of neutrino experiments that will continue to probe some of
nature's most fundamental questions.
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