Subject: FWD: Antimatter

From: "Marcus Pasram (516) 233-6869" <[email-masked]>
Date: Tue, 09 Jan 1996 11:56:33 -0500 (EST)

Subject: Antimatter
From: Salvatore Saieva <[email-masked]>
To: Friends -- Alan Rothstein <[email-masked]>, Alan Boord <[email-masked]>, Angella Chin <[email-masked]>, Jon Leong <[email-masked]>, Takamitsu Yanagihashi <[email-masked]>, Marcus Pasram <[email-masked]>, Al Perez <[email-masked]>, Robert Pescinski <[email-masked]>, Dave Richards <[email-masked]>, James Romano <[email-masked]>

By MALCOLM W. BROWNE 

c.1996 N.Y. Times News Service 

Physicists at the European Laboratory for Particle Physics announced on
Thursday that they had created, for 40 billionths of a second, the first
complete atoms of antimatter ever made by human beings or seen in nature. 

In an anti-atom, the antimatter equivalent of an ordinary atom, the
electrical charges of all the component particles are reversed; while an
ordinary atom has a positively charged nucleus with one or more negatively
charged electrons orbiting it, the antimatter atom has a negatively charged
nucleus with positively charged orbiting electrons. An ordinary atomic
nucleus contains positively charged protons, while its antimatter counterpart
contains negatively charged anti-protons. 

Unless an antimatter atom is kept from coming into contact with an ordinary
atom, the two atoms annihilate each other in a violent flash of energy _ a
fact that may explain the apparent absence of antimatter in the natural
universe. Anti-protons are routinely made in physics laboratories, as are
anti-electrons, which are also called positrons. But no one had heretofore
succeeded in nudging a positron into orbit around an anti-proton, making an
atom of antimatter. The announcement on Thursday by the European laboratory
near Geneva, known by its former acronym, CERN, establishes that this bizarre
kind of atom can actually exist. 

Physicists hope one day to make comparative measurements of the properties of
atoms and anti-atoms in terms of their gravitational attraction, their
interactions with light, and other features. Subtle differences between atoms
and their antimatter counterparts may shed light on the origin and evolution
of the universe and help solve the puzzle as to why we are made of matter
instead of antimatter. 

Although most physicists discount the idea that anti-hydrogen might one day
be developed as a very high potency fuel for interstellar rockets or
superbombs, some scientists have not abandoned the dream of exploiting
antimatter as a propellant. When combined with ordinary matter it
annihilates, converting mass to energy far more efficiently than does a
nuclear bomb. 

Dr. Walter Oelert of the Juelich Institute for Nuclear Physics Research in
Germany and his German and Italian colleagues reported that they created the
11 atoms of anti-hydrogen during a three-week experiment at CERN last
September, but withheld the news until they and independent experts had
thoroughly checked their results, which will be published in a forthcoming
issue of the journal Physical Review B. 

``We're absolutely sure now,'' he said in an interview, ``and the experiment
shows without doubt that anti-hydrogen can exist. No one really doubted it,
but it's nice to have the experimental proof.'' 

The anti-hydrogen atoms created in the experiment were moving at nearly the
speed of light and survived only some 40 billionths of a second before
colliding with atoms of ordinary matter and annihilating themselves. But from
the pattern and types of debris created by these collisions, the scientists
were able to establish the identity of the projectiles as anti-hydrogen
atoms. 

Dr. John Eades, the British coordinator of experiments at CERN, said that the
real challenge had been in producing enough of the right kind of collisions
between ordinary particles to create a few anti-hydrogen atoms. To do this,
anti-protons from one of CERN's accelerators were boosted to very high energy
and hurled into a target of xenon atoms, 

Some of the anti-protons survived and passed through, while others collided
with xenon nuclei, converting part of their collision energy into the
creation of anti-electrons (also called positrons). In a few very rare cases,
the speeds and directions of the newly born anti-electrons and the surviving
anti-protons coincided enough that the anti-electrons were captured into
orbits around the anti-protons, thus forming anti-hydrogen atoms. These
atoms, like ordinary hydrogen atoms, are electrically neutral, since the
charges of their components cancel each other. 

nn
But the neutrality of anti-hydrogen, like that of ordinary hydrogen, renders
it impossible to contain or manipulate using magnetic fields. Moreover, an
anti-atom cannot be contained in an ordinary vessel, since the slightest
contact with the container's wall causes it to annihilate. Consequently,
other groups are developing enormously sophisticated methods, including
interacting lasers, to manipulate and secure anti-particles inside vacuum
chambers. 

Oelert acknowledges that the anti-hydrogen atoms his group made cannot be
used as the basis of far-reaching experiments in the fundamental interactions
of physics, including such cosmological questions as to why the universe
seems to consist entirely of matter rather than antimatter. 

``We just wanted to have fun and see if you could make anti-hydrogen,'' he
said. ``It maybe is not such a great scientific achievement in itself,
because our anti-hydrogen atoms are moving around much too fast to study in
detail before they annihilate.'' 

Meanwhile, physicists at Harvard University, Pennsylvania State University,
Los Alamos National Laboratory, and other groups are attempting to create,
capture, and control anti-hydrogen in a more useful form. Their efforts focus
on ``cooling'' anti-protons and anti-electrons using lasers and other tools,
and assembling atoms not by violent collisions but by manipulation. Such
atoms, when they are eventually made, will be held almost motionless in their
chambers, isolated from contact with ordinary matter while their
gravitational, spectral, charge-conjugation, parity, and other
characteristics are measured. 

``Everyone makes shrewd guesses about the probable behavior of anti-hydrogen
and other anti-atoms,'' Eades said, ``and we don't really expect a big
surprise _ that an atom of antimatter would fall up instead of down, for
instance. But there may be subtle differences of great importance. For
instance, an atom and an anti-atom might fall at slightly different speeds
toward a gravitating object like the sun. Our orbit around the sun is
elliptical, so the sun's gravitational pull on the Earth varies slightly over
a year, and by observing its effect on an anti-hydrogen atom, we might learn
interesting things.'' 

In principle, scientists believe that atoms larger than anti-hydrogen _ the
simplest possible atomic form of antimatter _ might be created. But each
increase in the size and complexity of an atom complicates the assembly
problem. Anti-helium, the least complicated atom after hydrogen, would have a
nucleus of two anti-protons and two anti-neutrons, with two orbiting
anti-electrons. 

``We're especially interested in hydrogen and anti-hydrogen,'' Eades said,
``not only because of their structural simplicity, but because 90 percent of
the mass of the universe is hydrogen. Even slight differences in the
properties of hydrogen and anti-hydrogen could help explain why the universe,
as we know it, consists entirely of matter rather than antimatter.'' 

Dr. Gerald Gabrielse of Harvard University, whose research group is working
to slow down particles of antimatter contained in special traps, commented
that the CERN synthesis of anti-hydrogen ``is an important experiment
demonstrating that it can be done. The payoff will be down the road, when one
is eventually able to study the properties of these atoms.''