Number 239, September 8, 1995 by Phillip F. Schewe and Ben Stein
DO NEUTRINOS OSCILLATE? That is, do they mutate from one type into another,
violating a hitherto empirical law called conservation of lepton number?
Do neutrinos have a nonzero mass, an issue that has a bearing on the solar
neutrino problem and on the search for dark matter? Earlier this year,
unofficial reports (Update 213) from a Los Alamos experiment suggested
that neutrinos do oscillate. The findings of the Liquid Scintillator Neutrino
Detector (LSND) collaboration are now to be published in Physical Review
Letters (October 2, C. Athanassopoulos et al.). In this experiment muon
antineutrinos would presumably transform in flight into electron antineutrinos
which then enter a detector filled with 180 tons of mineral oil. There
they would occasionally strike a proton, creating a positron and a neutron.
Like the search for top quarks at Fermilab, the search for electron antineutrino
interactions at Los Alamos is a numbers game. After months of recording
data, the LSND team reports a harvest of 9 events with an expected background
of 2 events. In an unusual move, Physical Review Letters is publishing
in the same issue another article by a lone member of the group. James
Hill, a recent PhD at the University of Pennsylvania, believes that events
from more of the active detector volume should be excluded from the final
analysis, the better to reject spurious background contamination by, for
example, cosmic ray neutrinos entering the detector from the bottom. Hill's
alternative analysis renders 5 events against a background of 6 events,
which is the same thing as saying that no discernible neutrino oscillation
"signal" is present in the data. (Science journalists can obtain
copies of the two papers from AIP Public Information, physnews@aip.org)
THE OZONE HOLE CONTINUES TO DEEPEN. Ground-based measurements of the
total amount of ozone above the Halley research station in Antarctica showed
10 years ago that springtime (October) ozone levels were persistently falling
and were well below historic levels. A new report from the same site adds
another decade's worth of data, testifying to a continuing decline of ozone
each October and extension of the depletion period on into the Antarctic
summer (January and February). The researchers presenting the new data
point out that compliance with controls over manmade emissions of chlorofluorocarbons
(the biggest cause of ozone loss) should result in a stratospheric chlorine
peak in the late 1990s, after which (it is hoped) ozone recovery would
slowly ensue. However, only by the middle of the 21st century would chlorine
levels be as low as they were when the ozone hole was first discovered.
(A.E. Jones and J.D. Shanklin, Nature, 3 August, 1995.)
QUASAR WINDS , analogous to solar winds, are gusts of particles blown
away from quasars at speeds up to 10% the speed of light. Evidence for
the winds consists of peculiarities in the broad absorption lines observed
in the spectra of some quasars. The absorption occurs in gas that lies
between the quasar's central energy source (10**10 to 10**13 km away) and
observers on earth. A new study suggests that some of the absorbing gas
is transformed into the high-speed wind through the radiation pressure
exerted by the prodigious flux of light issuing from the quasar. (N. Arav
et al., Nature, 17 August 1995.)
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