Underground particle hunts
The dark matter experiments described
in “Mining for missing matter” (SN:
8/28/10, p. 22) sound almost identical
to those looking for neutrinos. Both are
placed deep underground to help screen
out background radiation, especially
neutrons. How do particle hunters differentiate between neutrino hits and
those by the putative dark matter particles? Also, the article makes it sound
like investigators think there is only one
type of [exotic] dark matter particle.
Why is that when there is an entire zoo
of normal matter particles and forces?
James Smith, San Jose, Calif.
Neutrinos, for the most part, would
deposit much more energy than that
expected for dark matter particles,
though a few rare types of neutrino interactions could produce signals similar to
those of dark matter particles. The sizes
of the detectors have been very different,
though, with dark matter detectors in the
10 to 100 kilogram range and neutrino
detectors upwards of 100,000 kilograms.
If much larger detectors have to be built
to detect dark matter, then neutrino
interactions may well prove to be a limiting background, says Dan Bauer of
Fermilab. He adds that, in fact, “most
theories do allow for an entire zoo of
exotic particles. However, most of these
particles will be either charged or decay
into other exotic particles. The particle
that makes up dark matter has to be neutral and stable to have survived for the
entire history of the universe. Typically,
this is taken to be the exotic particle with
the lowest mass, into which all other
exotic particles eventually decay.”
— Ron Cowen
Seeking truth with science
Wow! Harold Kroto is a scientist (“Treat
science right and it could help save
the world,” SN: 8/28/10, p. 32) who can
explain in lay terms what science is
and what we need to do to help young
people, who will soon be the ones deal-
ing with the catastrophe our planet
has become. Thank you. Spoken from a
stance of firm, but insightful argument.
Nanci Watkins, Frederick, Colo.
Mr. Kroto’s comments highlight a serious problem in today’s culture. The
loss of civility in our society has made
it popular to advance our particular
beliefs by attacking the failure of others rather than to focus on how we
can cooperate with the larger community to accomplish our goals. We have
developed many disciplines to help
order our lives. Science is only a recent
development. I think it is way too early
for science to claim the mantle of The
One and Only Ultimate Truth.
L.R. Davis, Margaretville, N. Y.
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November 6, 2010 | science news | 31
