Director-General of CERN, Mark Thomson.
| Photo Credit: Vinaya Deshpande

Scientists in Geneva took some antiprotons out for a spin — a very delicate one — in a truck, in a never-tried-before test drive that has been deemed a success.

If this so-called antimatter came into contact with actual matter, even for a fraction of an instant, it would have been annihilated in a quick flash of energy. So experts at the European Organization for Nuclear Research, known as CERN, over the course of four hours on Tuesday (March 24, 2026), brought about 100 antiprotons on the road.

The antiprotons were suspended in a vacuum inside a specially designed box and held in place by supercooled magnets.

After easing them from the lab and onto the truck, the scientists transported the antimatter on a half-hour drive to test how — if at all — the infinitesimal particles could be transported by road without seeping out. The antiprotons were then taken back to the lab in Tuesday’s (March 24, 2026) final stage that concluded with applause and a bottle of Champagne.

CERN spokeswoman Sophie Tesauri called the experiment successful. It was not immediately clear how many antiprotons had survived the entire journey, but roughly 91 of 100 were still there after the truck’s trip.

The hard part: Manipulating antimatter, like antiprotons, can be tricky business. As scientists understand the universe today, for every type particle that exists, there is a corresponding antiparticle, exactly matching the particle but with an opposite charge.

If those opposites come into contact, they “annihilate” each other, setting off lots of energy, depending on the masses involved. Any bumps in the road on the test journey that aren’t compensated for by the specially-designed box could spoil the whole exercise.

“The motivation behind these experiments is to compare matter and antimatter with extremely high accuracy and watch for differences which we might have not seen yet,” said Stefan Ulmer, the leader and spokesperson for Tuesday’s (March 24, 2026) experiment.

And Tuesday’s (March 24, 2026) practice was a first step toward making good on hopes, one day, to deliver CERN antiprotons to researchers at Heinrich Heine University in Düsseldorf, Germany, which is about eight hours away in normal driving conditions.

“We are scientists. We want to understand something about the fundamental symmetries of nature, and we know that if we do these experiments outside of this accelerator facility, we can measure 100 to 1000 times better,” Dr. Ulmer said.

The antiprotons were encased in a 1,000-kg box called a “transportable antiproton trap.” It was compact enough to fit through ordinary laboratory doors and fit on a truck. It used superconducting magnets cooled to -269°C (-452°F) that allowed the antiprotons to be remain suspended in a vacuum — not touching the inner walls, which are made of… matter.

The mass in the test — slightly less than that of about 100 hydrogen atoms — is so little, experts say, that the worst possible outcome was the loss of the antiprotons. Even if they did touch matter, any release of energy would be unnoticeable, only an oscilloscope, which picks up electrical signals, was be able to detect it.

The trap, says Ms. Tesauri, “is supposed to contain these antiprotons no matter what: if the truck stops, if it starts again, if it has to slam on the brakes — all that”. Work remains: The trap can contain the antiprotons on its own for only about four hours, and the drive to Düsseldorf is twice that.

The Geneva-based centre is best known for its Large Hadron Collider, a network of magnets that accelerates particles through a 27-km (17-mile) underground tunnel and slams them together at velocities approaching the speed of light. Scientists then study the results of those collisions.

But the sprawling, buzzing complex of scientific experiment is more than just about smashing atoms together: the World Wide Web, for example, was invented here by Britain’s Tim Berners-Lee in 1989.

Heinrich Heine University is seen as a better place to study antiprotons in-depth because CERN, with all its other activities, generates a lot of magnetic interference that can skew the study of antimatter.

But to get them there, those antiprotons will have to avoid touching anything on the way.

The centre’s Antiproton Decelerator, where a proton beam gets fired into a block of metal, causes collisions that generate secondary particles, including lots of antiprotons. It’s billed as a unique machine that produces low-energy antiprotons for the study of antimatter.

CERN’s “Antimatter Factory”, lab officials say, is the only place in the world where scientists can store and study antiprotons.

The centre has been experimenting with antimatter for years, and has made breakthroughs on measurement, storage and interaction of antimatter. Two years ago, the team transported a “cloud” of about 70 protons — not antiprotons — across CERN’s campus.

It was a similar drill this time, except that with antiprotons, a much better vacuum chamber is needed, according to Christian Smorra, head of a team behind the apparatus designed to store and transport antimatter.

Published – March 24, 2026 07:43 pm IST

A general view of the LHC experiment during a media visit at CERN near Geneva, Switzerland, July 23, 2014.
| Photo Credit: Reuters

Scientists at the world’s largest atom smasher expressed confidence Monday about moving forward with a multibillion-euro project to build a larger and more powerful particle collider that could help unlock more mysteries of the universe.

Leaders of the European Organization for Nuclear Research, or CERN, said planning is on track for its envisioned Future Circular Collider, which is estimated to cost 15 billion Swiss francs (about 16 billion euros or $17.2 billion) and is hoped to start operating in a first phase by 2040.

But nothing is certain yet, aside from the interest from mostly European and Western countries that bankroll CERN, which is home to the Large Hadron Collider. That project is perhaps best known for helping confirm the subatomic Higgs boson in 2012 after a decades-long quest for what was described as “the missing cornerstone of physics.”

“The Future Circular Collider is a possible facility. I’m saying ‘possible’ because we are today at the level of feasibility study. It’s not yet an approved project,” said Fabiola Gianotti, the CERN director-general. She said review committees had not turned up any “technical show-stoppers” for the project so far.

She touted the proposed collider as “a wonderful instrument to improve our understanding of fundamental physics” and a driver of innovation in areas like cryogenics, superconducting magnets, vacuum technologies and detector-instrumentation technologies that could offer socioeconomic benefits for society.

However, the science that the future collider could generate remains largely unknown. “It’s true that at the moment we do not have a clear theoretical guidance on what we should look for,” Gianotti said.

The laboratory that already houses what CERN leaders call the world’s biggest machine uses a network of magnets to accelerate particles through a 27-kilometer (17-mile) underground loop along the French-Swiss border and slam them together, capturing and interpreting the results of the collisions to help explain how fundamental physics works.

Monday’s briefing on the new collider included some proposed changes to the original plan announced in 2019. Among them: The loop will be 91 kilometers instead of the 100-kilometer circuit first envisioned.

But they still aim to boost energy levels of the particle collisions to 100 TeV, or 100 trillion electron volts, about eight times more powerful than the Large Hadron Collider’s 13TeV.

One way physicists seek clues to unravel the mysteries of the universe is by smashing matter together and inspecting the debris. But these types of destructive experiments, while incredibly informative, have limits.

We are two scientists who study nuclear and particle physics using CERN’s Large Hadron Collider near Geneva, Switzerland. Working with an international group of nuclear and particle physicists, our team realised that hidden in the data from previous studies was a remarkable and innovative experiment.

In a new paper published in Physical Review Letters, we developed a new method with our colleagues for measuring how fast a particle called the tau wobbles.

Our novel approach looks at the times incoming particles in the accelerator whiz by each other rather than the times they smash together in head-on collisions. Surprisingly, this approach enables far more accurate measurements of the tau particle’s wobble than previous techniques. This is the first time in nearly 20 years scientists have measured this wobble, known as the tau magnetic moment, and it may help illuminate tantalising cracks emerging in the known laws of physics.

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Why measure a wobble?

Electrons, the building blocks of atoms, have two heavier cousins called the muon and the tau. Taus are the heaviest in this family of three and the most mysterious, as they exist only for minuscule amounts of time.

Interestingly, when you place an electron, muon or tau inside a magnetic field, these particles wobble in a manner similar to how a spinning top wobbles on a table. This wobble is called a particle’s magnetic moment. It is possible to predict how fast these particles should wobble using the Standard Model of particle physics – scientists’ best theory of how particles interact.

Since the 1940s, physicists have been interested in measuring magnetic moments to reveal intriguing effects in the quantum world. According to quantum physics, clouds of particles and antiparticles are constantly popping in and out of existence. These fleeting fluctuations slightly alter how fast electrons, muons and taus wobble inside a magnetic field. By measuring this wobble very precisely, physicists can peer into this cloud to uncover possible hints of undiscovered particles.

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Testing electrons, muons and taus

In 1948, theoretical physicist Julian Schwinger first calculated how the quantum cloud alters the electron’s magnetic moment. Since then, experimental physicists have measured the speed of the electron’s wobble to an extraordinary 13 decimal places.

The heavier the particle, the more its wobble will change because of undiscovered new particles lurking in its quantum cloud. Since electrons are so light, this limits their sensitivity to new particles.

Muons and taus are much heavier but also far shorter-lived than electrons. While muons exist only for mere microseconds, scientists at Fermilab near Chicago measured the muon’s magnetic moment to 10 decimal places in 2021. They found that muons wobbled noticeably faster than Standard Model predictions, suggesting unknown particles may be appearing in the muon’s quantum cloud.

Taus are the heaviest particle of the family – 17 times more massive than a muon and 3,500 times heavier than an electron. This makes them much more sensitive to potentially undiscovered particles in the quantum clouds. But taus are also the hardest to see, since they live for just a millionth of the time a muon exists.

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To date, the best measurement of the tau’s magnetic moment was made in 2004 using a now-retired electron collider at CERN. Though an incredible scientific feat, after multiple years of collecting data that experiment could measure the speed of the tau’s wobble to only two decimal places. Unfortunately, to test the Standard Model, physicists would need a measurement 10 times as precise.

Lead ions for near-miss physics

Since the 2004 measurement of the tau’s magenetic moment, physicists have been seeking new ways to measure the tau wobble.

The Large Hadron Collider usually smashes the nuclei of two atoms together – that is why it is called a collider. These head-on collisions create a fireworks display of debris that can include taus, but the noisy conditions preclude careful measurements of the tau’s magnetic moment.

From 2015 to 2018, there was an experiment at CERN that was designed primarily to allow nuclear physicists to study exotic hot matter created in head-on collisions. The particles used in this experiment were lead nuclei that had been stripped of their electrons – called lead ions. Lead ions are electrically charged and produce strong electromagnetic fields.

The electromagnetic fields of lead ions contain particles of light called photons. When two lead ions collide, their photons can also collide and convert all their energy into a single pair of particles. It was these photon collisions that scientists used to measure muons.

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These lead ion experiments ended in 2018, but it wasn’t until 2019 that one of us, Jesse Liu, teamed up with particle physicist Lydia Beresford in Oxford, England, and realised the data from the same lead ion experiments could potentially be used to do something new: measure the tau’s magnetic moment.

This discovery was a total surprise. It goes like this: Lead ions are so small that they often miss each other in collision experiments. But occasionally, the ions pass very close to each other without touching. When this happens, their accompanying photons can still smash together while the ions continue flying on their merry way.

These photon collisions can create a variety of particles – like the muons in the previous experiment, and also taus. But without the chaotic fireworks produced by head-on collisions, these near-miss events are far quieter and ideal for measuring traits of the elusive tau.

Much to our excitement, when the team looked back at data from 2018, indeed these lead ion near misses were creating tau particles. There was a new experiment hidden in plain sight!

First measurement of tau wobble in two decades

In April 2022, the CERN team announced that we had found direct evidence of tau particles created during lead ion near misses. Using that data, the team was also able to measure the tau magnetic moment – the first time such a measurement had been done since 2004. The final results were published on Oct. 12, 2023.

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This landmark result measured the tau wobble to two decimal places. Much to our astonishment, this method tied the previous best measurement using only one month of data recorded in 2018.

After no experimental progress for nearly 20 years, this result opens an entirely new and important path toward the tenfold improvement in precision needed to test Standard Model predictions. Excitingly, more data is on the horizon.

The Large Hadron Collider just restarted lead ion data collection on Sept. 28, 2023, after routine maintenance and upgrades. Our team plans to quadruple the sample size of lead ion near-miss data by 2025. This increase in data will double the accuracy of the measurement of the tau magnetic moment, and improvements to analysis methods may go even further.

Tau particles are one of physicists’ best windows to the enigmatic quantum world, and we are excited for surprises that upcoming results may reveal about the fundamental nature of the universe.