Newsletter: Latest Antimatter Searches and Discoveries

Antimatter is the alter ego of normal matter, and one of my life-long special interests. A U.S. lab has announced a major new discovery, and NASA is about to launch a bold (some say fool-hardy) search for antimatter in space.


What is antimatter?


For each type of particle of normal matter, nature provides a corresponding type of antiparticle—electrons are matched by antielectrons, and charmed quarks by anti-charmed quarks, etc. Antielectrons have the same mass as electrons but all their other properties, such as electric charge, are the opposite.


When a particle meets its antiparticle all their properties exactly cancel one another except their mass energies. The result is cataclysmic—total annihilation. Normally, “annihilation” means destruction with some remaining trace of what existed before. But particle/antiparticle annihilation goes far beyond that. The mass energies may be converted into light, leaving no residue of any sort, no trace that either particle or antiparticle ever existed.


The intriguing mystery of antimatter is that virtually all of it has disappeared from our universe without all of the matter also disappearing. It’s well accepted that when our universe came into existence, it must have contained equal amounts of matter and antimatter, else it could not have emerged from nothing. When an antimatter particle annihilates, it takes a particle of matter with it into oblivion. So it seems that if all the antimatter disappeared through annihilation there would be no matter left as well—no stars, no planets, and no us. But nature provides an “out” that made life possible. Unlike every other force of nature, the lowly weak force treats matter and antimatter somewhat differently, as my Ph.D. thesis experiment demonstrated. This small difference allowed a small excess of matter to accumulate just after the Big Bang. Within the first one second, every one billion particles of antimatter were outnumbered by one billion and one particles of normal matter. The billions annihilated, leaving the one extra particle of matter, from which everything we see today is made.


Science cannot yet explain why this imbalance had this exact value (one in a billion), but we do know that if it had been even slightly more or slightly less, life would have been impossible. This is one of the captivating mysteries of our existence and a compelling research subject.


So, what’s new?


BNL, the Brookhaven National Laboratory in Long Island New York, announced this week that it has produced antihelium-4 nuclei, the largest piece of antimatter ever made by humans and possibly even by nature. Antihelium-4 nuclei each contain two antiprotons and two antineutrons, for a total of 12 antiquarks. Since each of those antiparticles is itching to destroy the next particle it can find, it is amazing that so many could be corralled into a single entity that lasts long enough to detect.


Antihelium-4 was discovered using BNL’s RHIC, the Relativistic Heavy Ion Collider by STAR, a collaboration of over 300 physicists from 54 institutions and 12 nations. STAR found a total of 18 nuclei of antihelium-4 by colliding gold nuclei against one another at energies of 100 billion electron volts (eV) per nucleon. Since gold nuclei contain 197 nucleons (79 protons and 118 neutrons), the total collision energy is over 39 trillion eV. By comparison, the LHC accelerator in Europe is now achieving 3.5 trillion eV per nucleon and total collision energies of 7 trillion eV, with single protons colliding with one another.


STAR’s record discovery may not be broken in the foreseeable future, since the next step would be antilithium-7, which will be one billion times harder to produce.



Sketch of STAR detecting antihelium-4 (red line) in gold-on-gold collision at BNL. Each yellow line is an individual particle produced in the same collision.


What’s coming up?


NASA will soon launch the Endeavor Space Shuttle on its last voyage. Aboard will be AMS, the Alpha Magnetic Spectrometer, designed to detect cosmic rays and antimatter coming toward us from outer space. The project leader is MIT Professor and Nobel Laureate Samuel C. C. Ting, considered eccentric even among high-energy physicists.


The LA Times said AMS “could upend astronomy in ways unparalleled since the Hubble Space Telescope…or could end up as a $1.5 billion hood ornament on the International Space Station.” Professor George Tarle of the University of Michigan said “There is little value in AMS. It’s actually a disgrace.”


AMS incorporates a multitude of complex devices designed to detect and identify high energy particles.  It includes a large permanent magnet, a superconducting magnet colder than outer space, a transition radiation detector, a time-of-flight system, a silicon detector to measure particle tracks, a ring-imaging Cerenkov detector, an electromagnetic calorimeter, anti-coincidence counters, a star-tracker and GPS alignment system. In other words, it’s got the whole nine yards of physics toys. The extremely powerful magnets are arranged in a “magic ring” to prevent interfering with the space station guidance systems.



Cosmic rays have been studied for about 100 years, leading to many important discoveries. Few expect any surprising new discoveries in this field—certainly not any that would upend astronomy as Hubble did. Perhaps we will find nothing new—perhaps AMS will indeed become a fabulously expensive hood ornament. But since nothing like this has ever been done before, this is unexplored territory. If we don’t look, we will never know what we might have missed.


AMS is designed to detect antinuclei among the vastly more common cosmic rays of normal matter, with a sensitivity of one in a billion. We might thereby learn more about our universe’s remaining antimatter, or more about dark matter. The greatest hope is that we will discover something that no one has yet imagined.





Dr. Robert Piccioni
Author of "Everyone's Guide to Atoms, Einstein, and the Universe"
and "Can Life Be Merely An Accident?"