PHYSICS NEWS UPDATE
The American Institute of Physics Bulletin of Physics News
Number 714 January 3, 2005
by Phillip F. Schewe, Ben Stein

NEUTRINO SUPERFLUIDS aren't going to be observed any time soon, but the
mathematical proof that they could exist helps to augment the catalog of
possible physical reality.  Superfluids are closely related to
superconductors.  In both phenomena numerous particles---whether boson
particles such as helium-4 atoms or pairs of fermion particles such as
electrons or helium-3 atoms---can coalesce into a single, all-encompassing
quantum state; examples include supercurrents, superfluids, and
Bose-Einstein condensates (BEC).  Joe Kapusta, a physicist at the
University of Minnesota, has shown that neutrinos too can become a
superfluid.  First they must pair up, as electrons do in superconductors. 
Two electrons with opposite spins can  form pairs by the exchange of slight
disturbances in the underlying matrix of atoms in the solid sample.
Analogously, neutrinos with opposite helicity (for a
"left-handed" neutrino, its intrinsic spin is oriented opposite
to its direction of motion; for "right-handed" neutrinos it's the
other way around) could pair up by exchanging a disturbance in the
all-pervasive sea of Higgs bosons in the universe.  (The Higgs boson, in
turn, is the much-sought cornerstone of the current standard model of
particle physics; it is the particle whose presence confers mass on many of
the other known particles.)  After pairing up, the nu pairs could then form
a superfluid condensate.  Kapusta admits that the chances of observing his
superfluid are slim since, first, right-handed neutrinos have never been
observed (and might be even more elusive or ghostly than their left-handed
partners) and, second, because the superfluid would only occur at
temperatures far colder than the 2.7-K average-temperature of the current
universe.  Kapusta points out that a superfluid of heavy neutrinos would
make a great medium for advanced civilizations to send messages over
intergalactic distances since the scattering length of pulses (the average
distance they go before scattering) moving through the neutrino fluid would
be much greater than for electromagnetic pulses. (Physical Review Letters,
17 December 2004; kapusta{at}physics.umn.edu)
                                                                
ANTI-HYDROGEN PRODUCTION UNDER LASER CONTROL has been achieved in an
experiment conducted at the CERN lab in Geneva.   Cold anti-hydrogen (Hbar)
atoms are the antimatter counterparts of hydrogen atoms. Previously
antihydrogen was formed when positrons cooled antiprotons within the
carefully designed electric and magnetic fields of a nested Penning trap.
That the anti-atoms had  formed at all was verified, but they're not yet
cold enough to be held in place.  The ultimate goal is to make a goodly
supply of anti-atoms, store them, and then probe their internal structure
with laser light to determine whether they have the same quantum behavior
as ordinary hydrogen. An incremental step would be not just to make the
anti-atoms but to see to it that they are in specific internal energy
states, and this is what the ATRAP (http://hussle.harvard.edu/~atrap/ )
collaboration has now done.  To gain some extra control over anti-H
production, they have to make the production process a bit more
complicated. Where the lasers come into the picture is to initiate a
three-step process.  First, laser light selectively excites cesium atoms
into special "Rydberg" states.  Second, positrons collide with
the Cs atoms, an encounter which cedes one of the atom's electrons to the
positron; the positron-electron pair, which constitutes a sort of atom-like
entity of its own, known as positronium (abbreviated Ps), inherits the
cesium atom's excitation.  (By the way, this excited Ps is a thousand times
bigger than plain Ps).  Third, the positron part of the Ps can occasionally
be captured by an antiproton moving in the same direction.  In the process
the anti-hydrogen atoms assumes the same binding energy as the former Ps. 
The rate for producing anti-H this way is still lower than with the older
methods, but the use of the intermediate cesium process and laser
excitation offers an extra measure of control over atomic conditions within
the trap (useful in experiments yet to come) and, furthermore, may have
resulted, in this case, in the coldest anti-atoms ever created in a lab. 
(Storry et al., Physical Review Letters, 31 December 2004; contact Gerald
Gabrielse, 617-495-4381,
gabrielse{at}physics.harvard.edu)

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