In a lab in Illinois, physicists captured and tamed a tiny particle of antimatter in a trap with invisible walls. By studying how the positron behaved, the researchers may soon have a chance to break our best mathematical model of physical reality.

The positron is the antimatter counterpart of the electron, which means the two particles have the same mass but the opposite electric charge. Unlike electrons, however, positrons are rare and typically exist for a tiny fraction of a second because the moment one meets one of the super-abundant electrons in our universe, the pair annihilate. This makes positrons difficult to study.

at Northwestern University in Illinois and his colleagues have now found a way to trap a positron and keep it around for months on end. By analysing data collected while the positron was trapped, they plan to precisely measure the antiparticle’s properties and consequently investigate one of the biggest problems with the standard model of particle physics.

The researchers obtained the positron from a radioactive isotope of sodium that emits one whenever it decays. Such positrons are very fast and hard to control, so they placed the sodium into a special refrigerator to lower its temperature and energy, and slow down the antiparticles.

They slowed them further by directing the positrons through a tungsten crystal. While some positrons were annihilated as they travelled through the crystal, some came through unscathed. They were then directed into a refrigerated chamber that was empty of all other particles. Here, electronic components generated electromagnetic fields that confined a single incoming positron, serving as invisible walls that trapped the particle.

The researchers then pushed the positron into its lowest possible energy state, which Gabrielse says allowed them to keep the otherwise elusive antiparticle trapped for months. They could also push it into the next lowest energy state with controlled bursts of microwaves.

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“It’s a real kick to stand in my lab and watch a positron making transitions – ‘quantum jumps’ we call them – between its lowest energy states. How much more fundamental, how much neater can it get?” he says.

“Trapping an antiparticle is extremely difficult,” says at Japanese scientific institute RIKEN, particularly since any stray particle, burst of light or tiny vibration could disturb it and the trap had to be kept just tenths of a degree above the coldest temperature possible.

The payoff for trapping and controlling the positron despite these experimental challenges could be remarkable. “This has the potential to become one of the most precise measurements of a fundamental constant in physics,” says Ulmer.

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Specifically, Gabrielse and his colleagues want to measure the positron’s magnetic moment, which is a number that quantifies its response to magnetic fields. The researchers have previously made the most precise ever measurement of the electron’s magnetic moment, and comparing this figure with the one for the antiparticle would enable them to compare the properties of matter and antimatter with unprecedented precision.

The standard model predicts they should have identical magnetic moments, but this prediction underscores a notable shortcoming of this theory. The problem is that if matter and antimatter are so alike, then they should have been created in equal amounts and fully annihilated as the universe began, leaving nothing. “The standard model seems to be inconsistent, or at least significantly incomplete, with basic features of the universe, like why we have a universe at all,” says Gabrielse.

Uncovering a difference between the electron and positron could hint at some currently unknown mechanism that resulted in our matter-filled universe. If all goes according to plan, the researchers aim to have data that will shed light on this within the year.

at the University of Wisconsin–Madison has won the 2026 Nobel prize in physics for his work on spotting ghostly particles called neutrinos using a detector at the South Pole.

Neutrinos are subatomic particles that rarely interact with material, are electrically neutral and perfuse the whole universe. Because of this, we can detect neutrinos that originated far away in the cosmos, trace their origin and learn more about the nature of the universe. Cosmic neutrinos are produced when a proton collides with another particle.

If you hold your hand out flat, more than a billion neutrinos will pass through it every second. These originate from the sun, but Halzen’s work concerns the much more rare and high-energy neutrinos coming from deep within the cosmos and what their detection can tell us about the universe.

Neutrinos act like “ghost-like messengers from the cosmos”, said , chair of the Nobel committee for physics, at a press conference. “It’s a way of bringing us information about distant cosmic sources which we’re unable to acquire in other ways.”

In 1988, Halzen proposed using the Antarctic ice as a neutrino detector, then went on to spearhead an international collaboration of more than 450 people from 58 institutions in 14 countries to make the IceCube Neutrino Observatory a reality.

The detector uses thousands of light sensors buried 2 kilometres under the surface of the ice in deep holes drilled using hot water. As neutrinos shoot through Earth, they interact with the ice, creating what’s known as Cherenkov radiation and emitting blue light. The network of light sensors allows researchers to trace their trajectory back to their origin point, revealing vital information about their formation.

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Halzen calculated that, if you built a neutrino collector 1 cubic kilometre in size, you would detect one neutrino per day. IceCube was completed in 2010 and began full operations the following year. The first high-energy extraterrestrial neutrinos were detected in 2013.

“When I reflect on this moment, I have to emphasise how lucky I was,” said Halzen, addressing the press conference by phone. “Because when we started this project, everybody realised this was maybe a good idea, but very few thought it would work – including myself. So this was kind of an adventure where success was not guaranteed, and we were lucky to overcome the various challenges. It was a long journey, but finally it worked.”

Halzen said he hopes the prize will reflect on the collaborators who worked on the project in the early days.

The IceCube detector has gone on to make many more discoveries. In 2017, it helped identify the first definitive source for a single high-energy cosmic neutrino: a blazar called TXS 0506+056 that blasted a huge jet of energy towards Earth. In 2023, it identified neutrinos from within our own galaxy, the Milky Way, which are typically overwhelmed by stronger signals from the rest of the universe.

Of winning the award, Halzen said: “It was a great surprise and I didn’t expect it. It’s a great pleasure.”

Researchers may have spotted the first signs of a dark matter particle. If the result is confirmed, it could be one of the most monumental discoveries in the history of physics.

Dark matter makes up about 85 per cent of matter in the universe, but for decades physicists have been unable to determine what it itself is made of. Hypotheses have ranged from different sorts of particles and forces to strangely behaving gravity and everything in between – but the leading idea has always been that of the weakly interacting massive particle, or WIMP. As we have built more and more powerful detectors to search for WIMPs, though, their failure to show up has led many to doubt their existence and move on to more exotic ideas.

That doubt may soon come to an end. A new analysis of data from the LUX-ZEPLIN (LZ) experiment in South Dakota has revealed a single particle that may be the first WIMP ever detected. “This result is certainly an exciting one, because it provides some potential positive hint for what dark matter could be, not just what dark matter could not be,” says at Brown University in Rhode Island, who wasn’t part of the analysis.

LZ looks for dark matter using a 7-tonne tank of liquid xenon, surrounded by several layers of shielding and buried more than a kilometre down to keep out other types of particles. When an outside particle hits a xenon atom, it creates a tiny burst of light that is measured by sensitive detectors surrounding the tank. Researchers can then use that light to reconstruct the path of the incoming particle and the energy level of the interaction.

In the search for WIMPs, we generally look for events with energies below about 30 kiloelectronvolts (keV), says LZ spokesperson , also at Brown University. That assumes the simplest sort of interaction, in which the WIMP is essentially bouncing off an individual nucleon in the xenon nucleus. Having not found any hints of WIMPs in that energy range, the LZ team decided to reanalyse the first 220 days of data from the detector, searching for events with higher energies.

That is where they found their dark matter particle candidate, at about 248 keV. “You must never make an assumption that nature is going to do something the easy way,” says Gaitskell. “Nobody can accuse our universe of making the simplest and most natural-seeming choices.”

Such a high-energy event can’t have come from the most simple type of interaction between a WIMP and a nucleon – instead, it must have happened through a more complicated coupling between the WIMP and the entire xenon nucleus. If that is the case, the WIMP must have a mass more than 200 times the mass of a proton.

“It’s not just that they’re seeing something, but that there’s a hint at what the underlying mechanism might be,” says at the University of California, Berkeley, who wasn’t involved in the analysis. “If this all stands up, our learning curve is going to be pretty steep from now on.”

Actually detecting a dark matter particle could reveal some of the universe’s most closely held secrets, including information about the early universe that is otherwise nearly impossible to determine, and drastically shake up our standard model of particle physics. But as Haxton says, this detection is not yet certain.

In particle physics, the statistical threshold for a finding to go from an intriguing hint to a solid discovery is a number called 5 sigma, which means there is about a 1-in-3.5 million chance that a signal like this would show up as a fluke rather than a true sign of dark matter. Right now, this detection from LZ sits at 2.6 sigma, which means that there is about a 1-in-200 chance it could appear as a fluke.

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That might still seem fairly secure, but in the search for dark matter it is far from enough. “In science we sit down and we do so many damned experiments, I’m afraid you come across a 1-in-100 event fairly often,” says Gaitskell.

“Before one can declare victory, you need a few more data points, but now they have something to aim for, they know where to look,” says Haxton. The good news is that this analysis only covered about one-third of the data that LZ has already taken, and other dark matter detectors around the world have their own data, as well. A few more events in the same energy range could bump the discovery of WIMPs up to 5 sigma – and change our understanding of physics and the universe forever.