archiv~1.txt: SETI [ASTRO] University Of Minnesota, Fermilab To Probe Nature Of

SETI [ASTRO] University Of Minnesota, Fermilab To Probe Nature Of

Larry Klaes ( )
Thu, 18 Mar 1999 15:22:42 -0500

>X-Authentication-Warning: majordom set sender
to owner-astro using -f
>Date: Thu, 18 Mar 1999 18:16:34 GMT
>From: Ron Baalke <>
>Subject: [ASTRO] University Of Minnesota, Fermilab To Probe Nature Of
>Reply-To: Ron Baalke <>
>University of Minnesota
>Sharon Butler, Fermilab, (630) 840-568
>Deane Morrison, University News Service, (612) 624-2346
>Earl Peterson, University of Minnesota, (612) 624-0319
>Stanley Wojcicki, Stanford University, (650) 926-2806
>Tom Fields, Fermilab, (630) 840-6316
>MINNEAPOLIS / ST. PAUL -- Physicists are preparing to go underground to
>solve one of nature's most baffling mysteries: whether the elusive subatomic
>particles known as neutrinos have mass. In search of a definitive answer,
>Fermi National Accelerator Laboratory in Chicago will send a beam of
>neutrinos underground to a University of Minnesota-run detection facility
>in Soudan Underground Mine State Park in northern Minnesota. Physicists will
>look for evidence that neutrinos leaving Fermilab change their character, or
>"flavor," before arriving at the mine a fraction of a second later; such a
>change would prove that neutrinos have mass.
>The university has selected the Hugo, Minn., firm Lametti & Sons to excavate
>the new underground laboratory in Soudan that will house the Minnesota
>detector for the $146 million neutrino experiment, called MINOS (Main
>Injector Neutrino Oscillation Search). The experiment, funded by the U.S.
>Department of Energy, the United Kingdom and the state of Minnesota, is
>expected to begin gathering data in 2002. Led by principal investigator
>Stanley Wojcicki (Voy-JIT-ski) of Stanford University, MINOS involves about
>200 scientists from 20 institutions in five countries. MINOS is part of
>Fermilab's NUMI (Neutrinos at the Main Injector) project, headed by
>physicist Tom Fields.
>Researchers hope that if the mass of neutrinos can be determined, so can
>their contribution to the total mass of the universe. Physicists estimate
>that about 80 to 90 percent of the mass in the universe is "dark matter":
>matter that can't be seen. Of this, neutrinos could account for as much as
>10 percent. If so, their combined mass -- and the gravity associated with
>objects that have mass -- could have played a role in the formation of stars
>and galaxies throughout the universe. Further, knowing how much, if any,
>mass is tied up in neutrinos might help physicists develop a Theory of
>Everything to explain gravity, electromagnetism and the forces operating
>in the atomic nucleus, all in the same terms.
>"Neutrinos are the lightest particles with mass, assuming they have mass,"
>said University of Minnesota physicist Earl Peterson. "We want to know what
>the family ties between neutrinos are, just as we already know the family
>ties between quarks -- the building blocks of protons and neutrons."
>Previous studies of neutrinos coming from the upper atmosphere have hinted
>that the particles may have mass and change flavor while in motion. But
>studying the behavior of atmospheric neutrinos is difficult and fraught with
>uncertainties. Starting with a controlled and well understood population of
>neutrinos generated by a particle accelerator should make it easier to sort
>out what's going on, the researchers said.
>"If the results from previous experiments turn out to be correct -- if,
>indeed, neutrinos have mass -- a new and very exciting area of scientific
>exploration will open up," said Wojcicki. "All of us are looking forward to
>being part of this adventure."
>Two things for certain about neutrinos: They have no electric charge, and
>they are exceedingly small. Therefore, they usually pass through the densest
>matter without bumping into anything. This makes them very hard to detect.
>The University of Minnesota detection facility in the old Soudan iron mine
>in Tower, Minn., will await the beam of neutrinos with about 10 million
>pounds of steel plates -- a huge, dense target to maximize the chance that
>neutrinos will hit an atomic nucleus.
>"We'll probably run the beam of neutrinos nine months of the year for four
>years," said Peterson. "Each pulse will contain trillions of neutrinos. We
>might get a neutrino interaction, or hit, in about one in a thousand pulses.
>Each hit will produce a spatial pattern of electrical signals in detectors
>between the steel plates."
>Neutrinos exist in three flavors: tau, muon and electron. They are produced
>naturally in the environment -- for example, within the sun. Neutrinos are
>also produced when very energetic cosmic rays -- nuclei of atoms streaming
>in from space -- crash into atoms in the atmosphere. The collisions produce
>sprays of subatomic particles, which decay to leave two muon neutrinos for
>every electron neutrino. However, experiments detect too few muon neutrinos
>to correspond with that ratio. This deficit suggests that muon neutrinos
>change -- or oscillate, as physicists put it -- into other kinds of neutrinos
>as they travel from the upper atmosphere to detectors on the Earth.
>Similarly, physicists in the MINOS experiment will be on the lookout for
>missing muon neutrinos. Fermilab will generate a beam of muon neutrinos and
>direct it through 445 miles of earth and rock to the Soudan mine in Tower,
>Minn. There, half a mile underground, the massive steel detector will
>determine whether the muon neutrinos all arrived, or whether some of
>them changed into other kinds en route. The detection must be performed
>underground to prevent interference from the millions of particles generated
>by cosmic rays. The beam from Fermilab will send a pulse of neutrinos every
>1.9 seconds. Each pulse will contain 300 trillion (300 million million)
>neutrinos. The distribution of neutrinos in the universe is about 300 per
>cubic centimeter.