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                    "October 21, 20263 min read Add Us On GoogleAdd SciAmFor the first time, scientists can make quantum measurements on a positron particle kondensator / ShutterstockYou can\u2019t 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\u2014the antimatter counterpart of the electron.On supporting science journalismIf you're enjoying this article, consider supporting our award-winning journalism by subscribing. By purchasing a subscription you are helping to ensure the future of impactful stories about the discoveries and ideas shaping our world today.\u201cThe big challenge is to persuade these positrons to slow down and then capture them,\u201d 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.Gerald GabrielseThe 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. \u201cEvery time they bang into something, there\u2019s a chance of annihilation, but it doesn\u2019t always happen,\u201d Gabrielse says. \u201cIf they make it to the end, they get popped out.\u201dNext, 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. \u201cIf you want to hold on to antimatter, you have to hold it in a container without walls,\u201d Gabrielse says.This method allowed the researchers to isolate and study a solitary, lone positron for a month\u2014and could let them do so indefinitely.The researchers intend to use their trap to make precise measurements of the positron\u2019s magnetic moment\u2014basically 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\u2019s 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. \u201cWe\u2019re looking to see if they have an exactly opposite magnetic moment,\u201d Gabrielse says. That\u2019s 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.\u201cTurn every particle to its antiparticle, look at physics through a mirror (flipping left and right) and press the \u2018rewind button\u2019 to reverse the flow of time,\u201d says Roni Harnik, a theoretical physicist at the Fermi National Accelerator Laboratory in Batavia, Ill., who was not involved in the project. \u201cOur most basic theories say that physics stays the same.\u201dIf it turns out things are different\u2014that the positron, for instance, has a different magnetic moment than the electron\u2014then we\u2019d have a hint about how matter won out.\u201cThis is an exciting development,\u201d Harnik says, \u201cthat will enable us to test a basic symmetry.\u201dSubscribe to Support Independent JournalismGreat science journalism requires human expertise, time, effort and creativity. And it costs money. That\u2019s why I and the journalists here at Scientific American hope you\u2019ll join our community.When you subscribe, you are supporting staff and freelance journalists who are passionate about telling science stories that are true, important and compelling. Our editors and reporters are often experts in their fields, which means they understand the nuances of big discoveries and can untangle the breakthroughs from the hype. With a subscription, you are also supporting rigorous fact-checking to ensure the words we publish are precise and accurate. And you\u2019re supporting original illustrations, graphics and photos that bring you closer to an advanced laboratory, an ice sheet in Antarctica or a space mission in orbit. You\u2019re helping us craft other types of high-quality journalism as well: Our newsletters are carefully written, edited and curated by staffers you have or will come to know and love. Our Science Quickly podcast is based on original reporting, collaboration with editors and scientists and exacting production.Subscriptions keep this engine running so we can continue to deliver thoughtful, rigorous and independent science journalism to you. In an era of viral misinformation, this work is crucial. If you value what we do, I hope you\u2019ll consider joining us as a subscriber"
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