"Physicists trap a single antimatter particle for a month" by Clara Moskowitz

Physicists trap a single antimatter particle for a month
For the first time, scientists can make quantum measurements on a positron particle
by Clara Moskowitz for Scientific American
Wed, October 21, 2026 at 8:00 AM PDT

You can't hold antimatter in your hand or even in a regular laboratory apparatus. As soon as antimatter meets matter, the two tend to annihilate each other. This makes studying antimatter tricky. But now physicists have managed to trap a single subatomic particle of the stuff for months at a time in a way that allows them to study its quantum states.

Further investigations using the trap might reveal the secret of why the world around us is made of matter and not antimatter, when things could have presumably gone either way.

Every normal particle of matter has an antimatter counterpart with equal mass but opposite charge. To build their trap, physicists started with atoms of sodium 22, a radioactive isotope with a half-life of about two and a half years. When one of these atoms decays, it emits a positron—the antimatter counterpart of the electron.

"The big challenge is to persuade these positrons to slow down and then capture them," says Gerald Gabrielse, a physicist at Northwestern University, who oversaw the project. The team reported its achievement on Wednesday in Physical Review Letters.

Gerald Gabrielse (top right) and his team in the lab where they trapped
a positron particle for a month. Courtesy Gerald Gabrielse

The first step is to send the positrons through the crystal lattice of a sliver of cold tungsten. As the particles go pinballing through the material, they slow down and lose energy. "Every time they bang into something, there's a chance of annihilation, but it doesn't always happen," Gabrielse says. "If they make it to the end, they get popped out."

Next, the physicists steer the positrons along a channel using electromagnetic fields. Eventually the particles end up in a vacuum, just three tenths of a degree Celsius above absolute zero, trapped by an electric field on top and bottom and a magnetic field on the sides. "If you want to hold on to antimatter, you have to hold it in a container without walls," Gabrielse says.

This method allowed the researchers to isolate and study a solitary, lone positron for a month—and could let them do so indefinitely.

The researchers intend to use their trap to make precise measurements of the positron's magnetic moment—basically the strength and orientation of its magnetic field. To do this, they must determine two things: the energy needed to flip the direction of the positron's spin and the energy needed to make it jump from its ground state to its first excited state.

Using a similar trap setup, Gabrielse and his team have already measured the magnetic moment of an electron to a precision of one part in 10 trillion. Taking the equivalent measurement for a positron will allow them to make a crucial comparison. "We're looking to see if they have an exactly opposite magnetic moment," Gabrielse says. That's the prediction of the Standard Model of particle physics. If the two have different values, however, this could help explain why our universe is made of matter instead of antimatter.

Just after the Big Bang, scientists think there were roughly equal amounts of the two. Most of the matter and antimatter must have annihilated, but a small excess of matter was somehow left over to seed the stars and planets we see. The magnetic moment measurement is just one of many realms where physicists are seeking differences between matter and antimatter to account for this profound discrepancy.

"Turn every particle to its antiparticle, look at physics through a mirror (flipping left and right) and press the 'rewind button' to reverse the flow of time," says Roni Harnik, a theoretical physicist at the Fermi National Accelerator Laboratory in Batavia, Ill., who was not involved in the project. "Our most basic theories say that physics stays the same."

If it turns out things are different—that the positron, for instance, has a different magnetic moment than the electron—then we'd have a hint about how matter won out.

"This is an exciting development," Harnik says, "that will enable us to test a basic symmetry."

https://www.scientificamerican.com/article/physicists-trap-a-single-antimatter-particle-for-a-month/

One Step Closer To Antimatter

From LiveScience.com:


Ephemeral Antimatter Trapped For Amazingly Long 16 Minutes

Antimatter, an elusive type of matter that's rare in the universe, has now been trapped for more than 16 minutes — an eternity in particle physics.

In fact, scientists who've been trapping antihydrogen atoms at the European Organization for Nuclear Research (CERN) in Geneva say isolating the exotic particles has become so routine that they expect to soon begin experiments on this rare substance.

Antimatter is like a mirror image of matter. For every matter particle (a hydrogen atom, for example), a matching antimatter particle is thought to exist (in this case, an antihydrogen atom) with the same mass, but the opposite charge.

"We've trapped antihydrogen atoms for as long as 1,000 seconds, which is forever" in the world of high-energy particle physics, said Joel Fajans, a University of California, Berkeley professor of physics who is a faculty scientist at California's Lawrence Berkeley National Laboratory and a member of the ALPHA (Antihydrogen Laser Physics Apparatus) experiment at CERN.

Trapping antimatter is difficult, because when it comes into contact with matter, the two annihilate each other. So a container for antimatter can't be made of regular matter, but is usually formed with magnetic fields.

In the ALPHA project, the researchers captured antihydrogen by mixing antiprotons with positrons — antielectrons — in a vacuum chamber, where they combine into antihydrogen atoms.

The whole process occurred within a magnetic "bottle" that takes advantage of the magnetic properties of the antiatoms to keep them contained. An actual bottle, made of ordinary matter, would not be able to hold antimatter because when the two types of matter meet they annihilate.

After the researchers had trapped antimatter in the magnetic bottle, they could then detect the trapped antiatoms by turning off the magnetic field and allowing the particles to annihiliate with normal matter, which creates a flash of light.

The team has now managed to capture 112 antiatoms in this new trap for times ranging from one-fifth of a second to 1,000 seconds, or 16 minutes and 40 seconds. (To date, since the beginning of the project, Fajans and his colleagues have trapped 309 antihydrogen atoms in various traps.)

And the researchers plan to improve on that, with the "hope that by 2012 we will have a new trap with laser access to allow spectroscopic experiments on the antiatoms," Fajans said in a statement. Those experiments would give researchers more information on the antimatter's properties.

In that way, it could help to answer a question that has long plagued physicists: Why is there only ordinary matter in our universe? Scientists think antimatter and matter should have been produced in equal amounts during the Big Bang that created the universe 13.6 billion years ago.

Today, however, there is no evidence of antimatter galaxies or clouds, and antimatter is seen rarely and for only short periods, for example, during some types of radioactive decay before it annihilates in a collision with normal matter.

The researchers detail their work on the antimatter trap in a new paper published online June 5 in the journal Nature Physics.

http://www.livescience.com/