Super-Kamiokande PR re Neutrino Mass Study

[Mike Grissom <mikeg@SLAC.Stanford.EDU>]

Radsafers,

Perhaps the biggest physics news story in many years,
if it holds up! (As Robert Parks said in last Friday's
Americal Physical Society's "What's New", it could have
serious implications for the Standard Model of the
Atom...)

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Official Super-Kamiokande Press Release

MEDIA ADVISORY for June 5,1998, Takayama, Japan

US EMBARGO EXPIRATION: 20:00 June 4, 1998, Pacific Daylight
Time

        EVIDENCE FOR MASSIVE NEUTRINOS

We announce today at "Neutrino '98", the international
physics conference underway in Takayama, Japan, that the
Super-Kamiokande Experiment has found evidence for non-zero
neutrino mass. Neutrinos are tiny, electrically neutral,
sub-atomic particles. Papers related to the results were
submitted to the scientific journals "Physical Review
Letters" and "Physics Letters." The experiment yields
results that are outside the standard theory of particle
physics, which describes the fundamental constituents of
matter and their interactions. Until now, there has been no
firm evidence that neutrinos possess mass.

The new evidence is based upon studies of neutrinos which
are created when cosmic rays, fast-moving particles from
space; bombard the earth' s upper atmosphere producing
cascades of secondary particles which rain down upon the
earth. Most of these neutrinos pass through the entire
earth unscathed. The Super-Kamiokande group uses a large,
50,000 ton tank of highly purified water, located about 1000
meters underground in the Kamioka Mining and Smelting
Company Mozumi Mine. Faint flashes of light given off by the
neutrino interactions in the tank are detected by more than
13,000 photomultiplier tubes that were manufactured for the
experiment by Hamamatsu Corporation.

By classifying the neutrino interactions according to the
type of neutrino involved (electron-neutrino or
muon-neutrino) and counting their relative numbers as a
function of the distance from their creation point, we
conclude that the muon-neutrinos are "oscillating."
Oscillation is the changing back and forth of a neutrino's
type as it travels through space or matter, This can occur
only if the neutrino possesses mass, The Super-Kamiokande
result indicates that muon-neutrinos are disappearing into
undetected tau-neutrinos or perhaps some other type of
neutrino (e.g., sterile-neutrino). The experiment does not
determine directly the masses of the neutrinos leading to
this effect, but the rate of disappearance suggests that the
difference in masses between the oscillating types is very
small. The primary result that we are reporting has a
statistical significance of more than 5 standard deviations.
An independent measurement based on upward-going muons in
the detector confirms the result at the level of more than 3
standard deviations.

The Super-Kamiokande Collaboration includes scientists from
23 institutions in Japan and the United States. Principal
funding for the experiment is provided by the Japanese
Ministry of Education, Science, Sports, and Culture
(Mombusho) while funding for the detector's outer most
region is provided by the United States Department of
Energy. In addition to advancing our understanding of basic
science, the collaboration has established a strong
international partnership between the Japanese and American
teams.

Since the beginning of its operation in April, 1996, the
Super-Kamiokande experiment has been the most sensitive in
the world for monitoring neutrinos from various sources. In
our studies, we have found interesting results in the
measurements of electron-neutrinos coming from the sun. The
number detected is about 35% of the number predicted by the
well established theoretical model of the sun's neutrino
producing processes. In addition, we obtained an indication
that the observed energy spectrum of those neutrinos is
deformed from the the predicted one. Super-Kamiokande's
observation of too few electron-neutrinos coming from the
direction of the sun also may be interpreted as due to
oscillations. We are continuing to study this exciting
possibility.

Reflecting on the significance of the new finding, we note
that massive neutrinos must now be incorporated into the
theoretical models of the structure of matter and that
astrophysists concerned with finding the 'missing or dark
matter' in the universe, must now consider the neutrino as
a serious candidate.

The Super-Kamiokande Collaboration

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See also related release, SUPER-KAMIOKANDE OPERATION
JEOPARDIZED BY BUDGET CUT. [This one not available?]

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The above may be viewed on the Web at URL:

http://www.slac.stanford.edu/slac/announce/9806-japan-neutrino/sk-pressrelease.html