Results from Fermilab experiment resolve long-standing neutrino question (Forwarded)
- From: Andrew Yee <ayee@xxxxxxxxxxxxxxxxxxxxxx>
- Date: Fri, 13 Apr 2007 15:25:52 -0400
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Fermilab
Media Contact:
Mike Perricone, Fermilab Office of Public Affairs
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Kurt Riesselmann, Fermilab Office of Public Affairs
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For immediate release: April 11, 2007
07-04
MiniBooNE opens the box
Results from Fermilab experiment resolve long-standing neutrino question
BATAVIA, Illinois -- Scientists of the MiniBooNE [1] experiment at the
Department of Energy's Fermilab [2] today (April 11) announced their first
findings. The MiniBooNE results resolve questions raised by observations of
the LSND [3] experiment in the 1990s that appeared to contradict findings of
other neutrino experiments worldwide. MiniBooNE researchers showed
conclusively that the LSND results could not be due to simple neutrino
oscillation, a phenomenon in which one type of neutrino transforms into
another type and back again.
The announcement significantly clarifies the overall picture of how
neutrinos behave.
Currently, three types or "flavors" of neutrinos are known to exist:
electron neutrinos, muon neutrinos and tau neutrinos. In the last 10 years,
several experiments have shown that neutrinos can oscillate from one flavor
to another and back. The observations made by the LSND collaboration also
suggested the presence of neutrino oscillation, but in a neutrino mass
region vastly different from other experiments. Reconciling the LSND
observations with the oscillation results of other neutrino experiments
would have required the presence of a fourth, or "sterile" type of neutrino,
with properties different from the three standard neutrinos. The existence
of sterile neutrinos would throw serious doubt on the current structure of
particle physics, known as the Standard Model of Particles and Forces.
Because of the far-reaching consequences of this interpretation, the LSND
findings cried out for independent verification.
The MiniBooNE collaboration ruled out the simple LSND oscillation
interpretation by looking for signs of muon neutrinos oscillating into
electron neutrinos in the region indicated by the LSND observations. The
collaboration found no appearance of electron neutrinos as predicted by a
simple two-neutrino oscillation scenario.
"It was very important to verify or refute the surprising LSND result," said
Robin Staffin, DOE Associate Director of Science for High Energy Physics.
"We never know what nature has in store for us. The MiniBooNE experiment was
an important one to do and is to be complimented for a job well done."
The MiniBooNE experiment, approved in 1998, took data for the current
analysis from 2002 until the end of 2005 using muon neutrinos produced by
the Booster accelerator at Fermilab. The MiniBooNE detector, located about
500 meters from the point at which the muon neutrinos were produced, looked
for electron neutrinos created by the muon neutrinos. The experiment's goal
was either to confirm or to refute the startling observations reported by
the LSND collaboration, thus answering a long-standing question that has
troubled the neutrino physics community for more than a decade.
"Our results are the culmination of many years of very careful and thorough
analysis. This was really an extraordinary team effort," said MiniBooNE
cospokesperson Janet Conrad of Columbia University. "We know that scientists
everywhere have been eagerly waiting for our results."
The MiniBooNE collaboration used a blind-experiment technique to ensure the
credibility of their analysis and results. While collecting their neutrino
data, the MiniBooNE collaboration did not permit themselves access to data
in the region, or "box," where they would expect to see the same signature
of oscillations as LSND. When the MiniBooNE collaboration opened the box and
"unblinded" its data less than three weeks ago, the telltale oscillation
signature was absent.
"We are delighted to see that the work of the MiniBooNE team has led to the
resolution of this puzzle," said Marv Goldberg, Program Director for
Elementary Particle Physics at the National Science Foundation. "We're proud
that our support yielded such an important breakthrough for neutrino physics
and we look forward to additional results from this team of university and
national laboratory scientists."
Although the MiniBooNE researchers have decisively ruled out the
interpretation of the LSND results as being due to oscillation between two
types of neutrinos, the collaboration has more work ahead.
"We have been studying the bulk of our data for several years," said
Fermilab physicist Steve Brice, analysis coordinator for the MiniBooNE
experiment, "but we have had access to these sequestered data for only a
short time. There are remaining analyses that we are eager to do next. They
include detailed investigation of data we observe at low energy that do not
match what we expected to see, along with more exotic neutrino oscillation
models and other exciting physics."
At this time, the source of the apparent low-energy discrepancy is unknown.
"It is great to get the MiniBooNE results out," said Fermilab Director Pier
Oddone. "It clears one mystery but it leaves us with a puzzle that is
important to understand."
The MiniBooNE collaboration will further analyze its data.
"As in many particle physics experiments, we have a result that answers some
questions and raises others," said MiniBooNE co-spokesperson William Louis,
Los Alamos National Laboratory, who also worked on the original LSND
experiment. "We live in interesting times."
For its observations, MiniBooNE relies on a detector made of a
250,000-gallon tank filled with ultrapure mineral oil, clearer than water
from a faucet. A layer of 1280 light-sensitive photomultiplier tubes,
mounted inside the tank, detects collisions between neutrinos made by the
Booster accelerator and carbon nuclei of oil molecules inside the detector.
Since January 2006, the MiniBooNE experiment has been collecting data using
beams of antineutrinos instead of neutrinos and expects further results from
these new data.
Notes for editors:
Scientists of the MiniBooNE collaboration will present their results at the
meeting of the American Physical Society in Jacksonville, Florida on April
16. Conference organizers have arranged for a press briefing at 1 PM (EDT)
on April 16.
[1] The MinibooNE experiment, formally known as the Booster Neutrino
Experiment, is an international collaboration of scientists involving 77
physicists from 17 institutions in the U.S. and the United Kingdom who
conduct the MiniBooNE experiment at Fermilab. MiniBooNE physicists are
supported by funding from the U.S. Department of Energy and the U.S.
National Science Foundation.
[2] Fermi National Accelerator Laboratory is a Department of Energy Office
of Science national laboratory operated under contract by the Fermi Research
Alliance, LLC. The DOE Office of Science is the single largest supporter of
basic research in the physical sciences in the United States.
[3] LSND is the Liquid Scintillator Neutrino Detector experiment at the
Department of Energy's Los Alamos National Laboratory.
MiniBooNE institutions:
1. University of Alabama
2. Bucknell University
3. University of Cincinnati
4. University of Colorado
5. Columbia University
6. Embry Riddle Aeronautical University
7. Fermi National Accelerator Laboratory
8. Imperial College-London (UK)
9. Indiana University
10. Los Alamos National Laboratory
11. Louisiana State University
12. University of Michigan
13. Princeton University
14. Saint Mary's University of Minnesota
15. Virginia Polytechnic Institute and State University
16. Western Illinois University
17. Yale University
Photos and graphics of the MiniBooNE experiment are available at:
http://www.fnal.gov/pub/presspass/images/BooNE-images.html
.
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