Cold antihydrogen atoms might have been made, for the first time,
in an experiment at the CERN
lab, where positrons and antiprotons are brought together in a bottle
made of electric and magnetic fields.

Nature allows the existence of antiparticles but hasn’t seen fit to
make a lot of them. Modest amounts of antiprotons show up in cosmic
ray showers, and positrons (antielectrons) are forged in certain high-energy
regions of the sky such as galactic nuclei.

But if larger forms of anti-matter like anti-atoms, anti-stars, and
anti-galaxies were plentiful in the visible part of the universe then
we would see the catastrophic gamma ray glare from places where matter
brushes up against antimatter. Such radiation has not been seen and
scientists must make their own anti-atoms artificially.

Making antihydrogen is difficult, however, because positrons and antiprotons,
even when they can be marshaled and brought near each other, are usually
going past each other too quickly for neutral atoms to form.

A few years ago a dozen or so hot antihydrogen atoms were made on the
fly amid violent scattering interactions at CERN and Fermilab (Updates
253,
297).
These did not dally long enough to be studied, but instead expired quickly
when they crashed into detectors that established the antihydrogen’s
brief existence.

At CERN several experiments are devoted to making cold anti-atoms in
a controlled environment amenable to detailed studies. The main goal
here is to determine whether the laws of physics (gravity, quantum mechanics,
relativity, etc.) apply to anti-atoms the same as they do to regular
atoms.

At this week’s meeting of the American Association for the Advancement
of Science (AAAS) in Boston, Gerald Gabrielse of Harvard, spokesperson
for the Antihydrogen Trap
Collaboration (ATRAP), reported new results.

In this experiment 6-MeV antiprotons (themselves made by smashing a
beam of protons into a target) are slowed by a factor of 10 billion
(to an equivalent temperature of 4 K), partly by mixing them with cold
electrons, and then collected in a trap. Positrons from the decay of
sodium-22 nuclei are cooled and collected at the other end of the device.
Eventually about 300,000 positrons are electrically nudged into the
vicinity of about 50,000 antiprotons.

Gabrielse believes that what sits in the trap isn’t entirely a neutral
plasma consisting of coincident positron and antiproton clouds, and
that cold antihydrogen atoms might have formed. More diagnostic equipment
being installed now may settle the issue in the coming months. A larger
version of the ATRAP apparatus, which might be in operation as early
as this fall, should allow the researchers to introduce some lasers
for the purpose of studying the spectroscopy of prospective anti-hydrogen
atoms in the trap.