Physicists zero in on the mass of the fundamental W boson particle

The team’s ultra-precise measurement confirms the Standard Model’s predictions.

Massachusetts Institute of Technology

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When fundamental particles are heavier or lighter than expected, physicists’ understanding of the universe can tip into the unknown. A particle that is just beyond its predicted mass can unravel scientists’ assumptions about the forces that make up all of matter and space. But now, a new precision measurement has reset the balance and confirmed scientists’ theories, at least for one of the universe’s core building blocks. 

In a paper appearing in the journal Nature, an international team including MIT physicists reports a new, ultraprecise measurement of the mass of the W boson. 

The W boson is one of two elementary particles that embody the weak force, which is one of the four fundamental forces of nature. The weak force enables certain particles to change identities, such as from protons to neutrons and vice versa. This morphing is what drives radioactive decay, as well as nuclear fusion, which powers the sun. 

Now, scientists have determined the mass of the W boson by analyzing more than 1 billion proton-colliding events produced by the Large Hadron Collider (LHC) at CERN (the European Organization for Nuclear Research) in Switzerland. The LHC accelerates protons toward each other at close to the speed of light. When they collide, two protons can produce a W boson, among a shower of other particles. 

Catching a W boson is nearly impossible, as it decays almost immediately into two types of particles, one of which, a neutrino, is so elusive that it cannot be detected. Scientists are left to measure the other particle, known as a muon, and model how it might add up to the total mass of its parent, the W boson. In the new study, scientists used the Compact Muon Solenoid (CMS) experiment, a particle detector at the LHC that precisely tracks muons and other particles produced in the aftermath of proton collisions. 

From billions of proton-proton collisions, the team identified 100 million events that produced a W boson decaying to a muon and a neutrino. For each of these events, they carried out detailed analyses to narrow in on a precise mass measurement. In the end, they determined that the W boson has a mass of 80360.2 ± 9.9 megaelectron volts (MeV). This new mass is in line with predictions of the Standard Model, which is physicists’ best rulebook for describing the fundamental particles and forces of nature. 

The precision of the new measurement is on par with a previous measurement made in 2022 by the Collider Detector at Fermilab (CDF). That measurement took physicists by surprise, as it was significantly heavier than what the Standard Model predicted, and therefore raised the possibility of “new physics,” such as particles and forces that have yet to be discovered. 

Because the new CMS measurement is just as precise as the CDF result and agrees with the Standard Model along with a number of other experiments, it is more likely that physicists are on solid ground in terms of how they understand the W boson.

“It’s just a huge relief, to be honest,” says Kenneth Long, a lead author of the study, who is a senior postdoc in MIT’s Laboratory for Nuclear Science. “This new measurement is a strong confirmation that we can trust the Standard Model.”

The study is authored by more than 3,000 members of CERN’s CMS Collaboration. The core group who worked on the new measurement includes about 30 scientists from 10 institutions, led by a team at MIT that includes Long; Tianyu Justin Yang PhD ’24; David Walter and Jan Eysermans, who are both MIT postdocs in physics; Guillelmo Gomez-Ceballos, a principal research scientist in the Particle Physics Collaboration; Josh Bendavid, a former research scientist; and Christoph Paus, a professor of physics at MIT and principal investigator with the Particle Physics Collaboration.

Piecing together

The W boson was first discovered in 1983 and is predicted to be the fourth heaviest among all the fundamental particles. Multiple experiments have aimed to narrow in on the particle’s mass, with varying degrees of precision. For the most part, these experiments have produced measurements that agree with the Standard Model’s predictions. The 2022 measurement by Fermilab’s CDF experiment is the one significant outlier. It also happens to be the most precise experiment to date.

“If you take the CDF measurement at face value, you would say there must be physics beyond the Standard Model,” says co-author Christoph Paus. “And of course that was the big mystery.”

Paus and his colleagues sought to either support or refute the CDF’s findings by making an independent measurement, with an experiment that matches CDF’s precision. Their new W boson mass measurement is a product of 10 years’ worth of work, both to analyze actual particle collision events and to simulate all the scenarios that could produce those events. 

For their new study, the physicists analyzed proton collision events that were produced at the LHC in 2016. When it is running, the particle collider generates proton collisions at a furious rate of about one every 25 nanoseconds. The team analyzed a portion of the LHC’s 2016 dataset that encompasses billions of proton-proton collisions. Among these, they identified about 100 million events that produced a very short-lived W boson.

“A particle like the W boson exists for a teeny tiny moment — something like 10-24 seconds — before decaying to two particles, one of which is a neutrino that can’t be measured directly,” Long explains. “That’s the tricky part: You have to measure the other particle — a muon — really well, and be able to piece things together with only one piece of the puzzle.”

Gathering momentum

When a muon is produced from the decay of a W boson, it carries half of the W boson’s mass, which is converted into momentum that carries the muon away from the original collision. Due to the strong magnetic field inside the CMS detector, the electrically charged muon follows a path whose curvature is a function of its momentum. Scientists’ challenge is to track the muon’s path and every interaction it may have with other particles and its surroundings, in order to estimate its initial momentum. 

The muon’s momentum is also influenced by the momentum of the W boson before it decays. Decoding the impact of the W boson’s motion from the effects of its mass presented a major challenge. To infer the W boson mass, the team first carried out simulations of every scenario they could think of that a muon might experience after a proton-proton collision in the chaotic environment of the particle collider. In all, the team produced 4 billion such simulated events described by state-of-the-art theoretical calculations. The simulations encoded diverse hypotheses about how the muon momentum is affected by the physical features of the CMS detector, as well as uncertainties in the predictions that govern W boson production in LHC collisions.

The researchers compared their simulations with data from the 2016 LHC run. For every proton-proton collision event that occurs in the collider, scientists can use the CMS detector at CERN’s LHC to precisely measure the energy and momentum of resulting particles such as muons. The team analyzed CMS measurements of muons that were produced from over 100 million W boson events. They then overlaid this data onto their simulations of the muon momentum, which they then converted to a new mass for the W boson. 

That mass — 80360.2 ± 9.9 megaelectron volts — is significantly lighter than the CDF experiment’s measurement. What’s more, the new estimate is within the range of what the Standard Model predicts for the W boson’s mass, bolstering physicists’ confidence in the Standard Model and its descriptions of the major particles and forces of nature.

“With the combination of our really precise result and other experiments that line up with the Standard Model’s predictions, I think that most people would place their bets on the Standard Model,” Long says. “Though I do think people should continue doing this measurement. We are not done.” 

“We want to add more data, make our analysis techniques more precise, and basically squeeze the lemon a little harder. There is always some juice left,” Paus adds. “With a better look, then we can say for certain whether we truly understand this one fundamental building block.” 

This work was supported, in part, by multiple funding agencies, including the U.S. Department of Energy, and the SubMIT computing facility, sponsored by the MIT Department of Physics. 

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Written by Jennifer Chu, MIT News

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Journal

Nature

Article Title

"High-precision measurement of the W boson mass with the CMS experiment”

 

How Iran’s strike on Qatar is choking the global AI economy

Ras Laffan, Qatar / Matthew Smith @ Flickr

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By External contributor March 26, 2026

The Shot Nobody Heard

On March 2, 2026, the world’s largest liquefied natural gas facility went dark. QatarEnergy’s Ras Laffan Industrial City, a sprawling complex on the northeastern coast of Qatar that processes the colossal reserves of the North Field gas reservoir, halted all production following a wave of Iranian drone strikes. The state energy company declared force majeure two days later, freeing itself from contracted supply obligations to customers across Europe and Asia. It was, by any measure, a seismic economic event. And yet the full significance of what had been lost barely registered in the mainstream financial press.

The conversation that followed was dominated, predictably, by LNG. Energy markets convulsed.

European gas futures spiked. Asian buyers scrambled for alternative cargoes. QatarEnergy CEO

Saad al-Kaabi confirmed to Reuters that the damage, described by his own executives as “extensive”, had knocked out approximately 17% of Qatar’s LNG export capacity, representing an estimated $20bn in lost annual revenues. The cost of repairing the damaged trains was put at $26bn, with a recovery timeline measured not in months but in years, ranging from three to five years according to QatarEnergy’s own assessment.

But buried beneath the LNG story was a revelation with far more profound implications for the global economy: the same facility was simultaneously the world’s second-largest producer of helium. And with Ras Laffan offline, roughly one-third of the planet’s helium supply had vanished overnight.

What Helium Actually Does, And Why Nothing Else Can

To most people, helium is the gas that fills party balloons. To the semiconductor industry and by direct extension, to the entire edifice of modern artificial intelligence, it is something closer to oxygen. Without it, advanced chip manufacturing at sub-5-nanometre geometries, the frontier on which the AI race is being fought, is simply not possible.

Semiconductor manufacturing requires ultra-pure helium at multiple critical stages. During lithography, the process by which circuit patterns are etched onto silicon wafers with extraordinary precision helium is injected between the wafer and its carrier to dissipate heat and prevent warping. In extreme ultraviolet (EUV) lithography, the technology that enables the production of the most advanced chips now powering AI accelerators, helium maintains the near-perfect vacuum environments and cooling systems without which the process fails entirely. Helium is also the only gas suitable for leak detection in these hermetically sealed environments, and it is used in the purging of process chambers where the presence of any reactive gas would destroy a wafer batch worth hundreds of thousands of dollars.

Unlike nitrogen or argon, which can be substituted in various industrial applications, helium has no viable replacement in semiconductor-grade manufacturing. As a noble gas, it is chemically inert, its atomic radius is the smallest of any element stable at industrial temperatures, and its thermal conductivity is uniquely suited to the precision demands of modern fabs. As chip geometries continue to shrink and EUV adoption expands across the industry, each wafer actually consumes more helium than the last generation. Demand is not linear; it is accelerating.

Beyond semiconductors, helium’s industrial reach is vast and largely unappreciated.

Healthcare systems depend on it critically: MRI machines require approximately 1,500 litres of liquid helium to cool their superconducting magnets, and the healthcare sector accounts for roughly 30% of all global helium consumption. Aerospace propulsion and rocket testing programs, including those operated by NASA, SpaceX, and Blue Origin, use helium to purge fuel lines and pressurise propellant tanks. The fibre optics industry uses it to draw glass filaments. Scientific research from particle physics at CERN to NMR spectrometry in pharmaceutical laboratories depends on its cryogenic properties. Even the food industry employs helium in modified atmosphere packaging to extend shelf life. The entertainment industry uses it for everything from concert rigging to LED cooling systems. The loss of a third of the global supply does not affect one sector; it threatens all of them simultaneously.

The Golden Thread: Helium, Chips, and the AI Trillion-Dollar Stack

To understand the true scale of what is now at risk, one must map the architecture of the global AI investment chain and trace helium’s role through every link.

The global semiconductor industry is, by conservative estimates, already a $600bn annual market, with projections placing it at $1 trillion in revenues before the end of the decade. This industry is the physical substrate of the artificial intelligence revolution. Every large language model, every AI accelerator deployed in a data centre, every GPU cluster running inference on demand exists because of chips manufactured at the atomic scale in a handful of facilities concentrated in Taiwan, South Korea, the United States, and Japan.

TSMC, the Taiwan Semiconductor Manufacturing Company, is the single most strategically critical node in this chain. It produces approximately 90% of the world’s most advanced logic chips, and it is the sole foundry for NVIDIA’s AI accelerators, the GPUs that have become the defining hardware of the AI era. NVIDIA’s market capitalisation recently exceeded $3 trillion, making it among the most valuable companies in history, built almost entirely on the insatiable demand for AI compute. TSMC also manufactures the processors inside Apple’s iPhone and MacBook product lines, AMD’s Ryzen and Instinct series, and Qualcomm’s Snapdragon chips.

South Korea is the second great pillar. Samsung and SK Hynix together produce the overwhelming majority of the world’s High Bandwidth Memory (HBM), the specialist DRAM chips that are stacked alongside NVIDIA’s GPUs in AI accelerators and are, in many ways, just as indispensable as the GPU itself. Without HBM, an NVIDIA Blackwell or Hopper chip cannot function at AI-relevant speeds. Samsung and SK Hynix also produce the NAND flash memory inside virtually every consumer device on Earth, from smartphones to cloud storage systems.

Here is where the helium thread becomes the golden thread. South Korea sourced 64.7% of its helium from Qatar in 2025. The Ras Laffan facility supplied Samsung’s M15 and M16 memory manufacturing plants and SK Hynix’s facilities directly, via long-term contracts with industrial gas distributors including Linde, Air Liquide, Messer, and Iwatani. With Ras Laffan offline, a monthly shortfall of 5.2 million cubic metres of helium has appeared in the market. Spot prices doubled within days of the initial shutdown and are expected to continue rising.

The semiconductor demand for helium is not static. With TSMC, Samsung, and Intel all ramping EUV-based manufacturing nodes under government-backed CHIPS Act programs and their international equivalents, the industry’s helium consumption is projected to grow by 15-20% annually through the end of the decade. The crisis has arrived at precisely the moment of maximum vulnerability.

The GCC’s Enormous Stake and the Bitter Irony

Iran’s IRGC, whether by design or miscalculation, has struck with particular force at a target that is intimately connected to the investment portfolios of its Gulf neighbours. The irony is almost too precise to be accidental.

The Gulf Cooperation Council states have, over the past several years, positioned themselves as among the most significant sovereign investors in the global AI and semiconductor ecosystem. Abu Dhabi’s MGX fund, with ambitions reaching $100bn in assets under management, has invested directly in OpenAI, NVIDIA, and data centre infrastructure. The UAE’s G42, backed by Abu Dhabi sovereign wealth, signed deals granting access to 500,000 NVIDIA chips. Saudi Arabia’s Public Investment Fund, through its Alat subsidiary, has committed $100bn by 2030 to advanced electronics manufacturing, including a $10bn AI chip partnership with AMD and a separate partnership with NVIDIA to supply hundreds of thousands of Blackwell-generation GPUs to the Kingdom’s Humain AI initiative. Qatar’s own sovereign wealth vehicle, the Qatar Investment Authority, positioned itself as an anchor investor in Ardian Semiconductor, a dedicated chip investment fund.

These are not passive financial positions. They represent a collective sovereign bet measured in hundreds of billions of dollars on the AI and semiconductor industries as the defining growth driver of the coming decade. And those industries sit downstream of a helium supply chain that Iran has now partially severed, originating in Qatar’s own backyard. The attacker has struck at the infrastructure that underpins the wealth creation strategy of the entire region.

Stored Reserves, Shrinking Buffers, and the Coming Crunch

The immediate response from chip industry executives has been measured. TSMC confirmed that it maintains more than two months of helium inventory and sources from multiple suppliers. SK Hynix stated publicly that it had diversified its procurement and secured adequate short-term reserves. South Korea’s Ministry of Trade, Industry and Resources launched an emergency review of supply dependencies across 14 critical semiconductor materials, with helium and bromine — another input sourced heavily from the region — at the top of the list.

But the composure of these initial statements should not be mistaken for security. Analysts who have examined the actual inventory levels with granular precision paint a more alarming picture.

South Korea holds approximately six months of helium inventory at normal production rates. The critical qualifier is ‘normal.’ HBM production for AI accelerators has been running at exceptional intensity throughout 2026, with NVIDIA’s Blackwell demand absorbing virtually all available memory capacity. At current burn rates, the effective buffer for Korean fabs is closer to three to four months before real production cutbacks become unavoidable placing the acute phase of the crisis in the late summer or early autumn of this year.

Fitch Ratings warned in a note on March 17 that “credit risk would worsen if supply shortages exceeded inventory buffers, resulting in higher-cost sourcing, increased working-capital needs and production prioritisation.” Bank of America analysts noted that helium demand is concentrated in high-value, mission-critical applications where “supply security is typically prioritised over price,” allowing suppliers to push pricing substantially higher during disruptions. Linde and Air Products, the dominant industrial gas distributors, have already seen share prices rise 14 to 15% year-to-date — a telling signal of where the smart money sees the crisis heading.

Airgas, a major US helium distributor, declared its own force majeure on March 17 and moved immediately to prioritise healthcare customers, telling semiconductor clients to expect as little as half their normal monthly deliveries, with an immediate surcharge of $13.50 per hundred cubic feet. The rationing has begun.

The Revenue Mathematics of Catastrophe

The financial arithmetic of this crisis is sobering. QatarEnergy’s CEO has confirmed that the damaged infrastructure representing 17% of LNG export capacity and 14% of helium output  generates an estimated $20bn in lost annual revenues, across LNG, helium, condensate, LPG, naphtha, and sulphur. The cost of rebuilding the destroyed LNG trains is put at $26bn, with a recovery timeline of three to five years at minimum.  

Over a five-year shutdown of the affected capacity, the cumulative revenue loss to QatarEnergy could approach $100bn.

The downstream cost to the semiconductor industry is harder to quantify with precision, but analysts provide suggestive parameters. A 60 to 90 day severe helium squeeze could push delivered helium costs for the most exposed buyers by 25 to 50% , with the sharpest impact on those with weaker long-term contract protection. If the disruption forces Korean fabs to reduce output on lower-margin chips and potentially even begin rationing production runs on higher-value AI memory the  

financial consequences ripple instantly through the entire NVIDIA-AMD AI accelerator supply chain, into data centre expansion programs, and ultimately into the earnings guidance of every major technology company that has committed to aggressive AI infrastructure investment.

Morgan Stanley’s Head of Asia Technology Research, Shawn Kim, articulated the systemic risk precisely: “A disruption in the Strait of Hormuz wouldn’t automatically halt chip production, but it could ripple through power costs, materials supply, and the economics of building AI infrastructure.” The $650bn in planned AI investments globally that Bloomberg mapped out earlier this year all sit downstream of a supply chain whose critical vulnerability has just been exposed.

The Broader Cascade: Beyond Chips and AI

The helium crisis does not begin and end with semiconductors. Its breadth across industries reveals just how deeply a single invisible gas is woven into the fabric of the modern economy.

In healthcare, the consequences are already visible. The medical imaging sector — which accounts for roughly 30% of global helium consumption  is acutely exposed. MRI machines require approximately 1,500 liters of liquid helium to cool their superconducting magnets, with periodic top-ups throughout the machine’s operational life. Helium shortages historically translate directly into delayed or cancelled MRI procedures, deferred hospital upgrades, and rising diagnostic costs that fall hardest on patients in lower-income healthcare environments. “There will be MRIs that go down,” one senior industry figure told Euronews this week. In India, where helium is imported almost entirely from Qatar, healthcare system administrators are already preparing for higher scan costs and supply chain disruption to essential consumables.

In aerospace, SpaceX, Blue Origin, and Rocket Lab all depend on helium for rocket propulsion systems for purging fuel lines, pressurising propellant tanks, and testing systems under controlled conditions. Delays in helium availability translate directly into launch schedule slippage, with cascading consequences for commercial satellite programs and government space contracts.

In scientific research, particle physics facilities, pharmaceutical NMR laboratories, and university research programs have historically been among the first casualties of helium shortages. Research at Harvard, MIT, and comparable institutions was suspended during the 2012 and 2019 helium crises. A prolonged shortage in 2026 would interrupt entire programs of fundamental research at the moment when competition with China in AI and quantum computing research is most intense.

In food processing, modified atmosphere packaging — which extends shelf life for fresh produce, meat, and prepared foods — relies on helium blends in some applications. In the entertainment and events industry, precision cooling systems and high-altitude rigging balloons use helium in volumes that, while small by industrial standards, are practically irreplaceable.

Yet the outsized significance of the semiconductor and AI crisis dwarfs all of these. Healthcare, aerospace, and research are serious; the disruption of the AI hardware supply chain is potentially systemic. The chip industry is not merely an industry; it is the infrastructure upon which every other industry’s digital transformation now depends. A prolonged, severe helium shortage that forces fabs to reduce output does not just cost NVIDIA or Samsung revenue. It delays the AI buildout that every major corporation, every government digital strategy, and every sovereign wealth fund’s investment thesis has been predicated upon.

Can the Industry Pivot? The Uncomfortable Truth

The uncomfortable answer is: not quickly, and not completely. Several alternative helium sources exist. The United States is the world’s largest producer, primarily through reserves in Texas, Kansas, and Wyoming. Algeria is a significant secondary producer. Russia holds substantial reserves. But the capacity to ramp these sources to compensate for the sudden loss of a third of global supply is simply not there.

Building new helium extraction and liquefaction infrastructure is a multi-year proposition. Helium is a byproduct of natural gas processing, not a standalone product; you cannot build a helium plant without a compatible gas field. Qualifying new suppliers through the semiconductor industry’s rigorous purity and reliability standards adds further time. Phil Kornbluth, the industry’s most respected independent analyst, was blunt: “Your best-case scenario would be you’re back producing some helium in six weeks. As it looks right now, that’s highly unlikely.”

Some progress is being made at the margins. Samsung has deployed a Helium Reuse System (HeRS) on select production lines since 2025, capable of recovering and recycling used helium with projected savings of roughly 18.6% of total annual consumption if fully deployed. Siemens Healthineers and Philips have been developing helium-free MRI technology for years, though deployment at scale remains limited. These are meaningful steps, but they are mediumterm solutions to what is now an immediate crisis.

Russia holds large helium reserves, primarily at the Amur processing facility in Eastern Siberia. But engaging Russian suppliers at scale requires navigating a labyrinth of sanctions, compliance risk, and geopolitical exposure that most Western and Asian corporations are unwilling to accept. China, which has been aggressively building domestic helium production capacity, is in no mood to share its strategic reserves with a West that has been weaponising export controls against its own semiconductor industry.

The industry is not staring into the abyss today. It is staring at a 90-day countdown, at the end of

which, if QatarEnergy has not resumed production and the Strait of Hormuz remains constrained, the choices become genuinely painful.

The Asymmetric Logic of Iran’s Strike

For those who study asymmetric warfare and Iran’s IRGC has become its most accomplished practitioner the strategic logic of the Ras Laffan strikes is elegant in its brutality. A conventional military adversary measures success in territory captured or forces destroyed. The IRGC measures it in cascading economic costs imposed on an adversary’s extended network and few single targets in the world economy offered a higher return on disruption than the Ras Laffan complex.

A single facility hit has simultaneously: disrupted European energy security, shocked Asian LNG import markets, triggered force majeure on contracts stretching from Italy to South Korea, imperilled the GCC’s sovereign investment strategies in AI and semiconductors, constrained the medical imaging capacity of dozens of countries, and injected uncertainty into a $3 trillion company’s supply chain. The UAE’s industry minister Sultan Al Jaber described Iran’s attacks as “global economic warfare,” adding that “energy flows are being weaponised.” He was right, but the description was incomplete. It is not only energy flows. It is the invisible gas that nobody wrote about, flowing silently through the pipes of the most advanced industrial civilisation in history, that has been weaponised too.

What Executives Must Confront

When the supply chain executives of the chip and AI industry fully process the implications of what has occurred at Ras Laffan, their most acute challenge will not be explaining a missed quarter to their boards. It will be confronting the foundational assumption error that has governed their industry for a decade: that geopolitical risk was someone else’s problem, and that just-in-time supply chains could be managed through diversification spreadsheets rather than genuine resilience architecture.

The helium dependency on Qatar was not a secret. The Semiconductor Industry Association warned explicitly in 2023 that a helium supply disruption would “likely cause shocks to global semiconductor manufacturing.” That warning was filed, noted, and largely ignored. The cost of ignoring it is now being calculated in real time.

The questions that will define boardroom conversations in Seoul, Taipei, Santa Clara, and Riyadh over the coming weeks are searching and uncomfortable. How long does the actual inventory last at real production rates? What is the contractual exposure if force majeure declarations cascade through the industrial gas distribution chain? Can delivery timelines for NVIDIA’s Blackwell architecture be maintained, and what happens to data centre expansion commitments if they cannot? Which customers get priority allocation, and who absorbs the cost of being deprioritised? How does a $100bn sovereign AI strategy in Riyadh or Abu Dhabi remain on track when the physical hardware it depends upon cannot be manufactured at scale?

These are not hypothetical questions. They are live, they are urgent, and the window for acting ahead of the crisis rather than inside it is narrowing rapidly.

The Unwritten Story of a Written Crisis

The Economist noted this week that “a dangerous contradiction is evident in markets”: investors are unnerved by war, yet asset prices remain staggeringly optimistic. The contradiction deepens when one examines the helium story, because this particular risk is almost entirely unpriced.

Markets have absorbed the LNG disruption. They have begun to factor in energy price volatility. They have not yet priced a multi-year constraint on one-third of global helium supply into the valuations of NVIDIA, TSMC, Samsung, SK Hynix, or any of the AI infrastructure companies whose capital programmes depend on an uninterrupted flow of advanced chips. When that reckoning arrives and it will, whether in three months, six months, or twelve — it will not feel like a supply chain adjustment. It will feel like a correction in assets that had been priced for a world in which the physics of chip manufacturing were immune to the violence of geopolitics.

ECHo collaboration: Hunting for the neutrino mass with “cool” detectors

New upper limit determined – Current research results are the basis for large-scale experiments to get closer to the mass of “ghost particles”

Heidelberg University

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image: 

The photo shows a detector module for the ECHo experiments developed and built at the Kirchhoff Institute for Physics. The detector chip is located in the middle; the four surrounding chips contain the Superconducting Quantum Interference Devices that read out the signals.

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Credit: © ECHo Collaboration

Their mass is extremely low, but how light are neutrinos really? A collaboration comprising German and international research groups has optimized its experiments to determine the mass of these “ghost particles”. In doing so, they succeeded in further adjusting downward the upper limit on the neutrino mass scale that had previously been determined in similar experiments. As part of the “Electron Capture in Ho-163 Experiment” (ECHo), the researchers are using the isotope Holmium-163 (Ho-163), whose decay processes allow for conclusions on the neutrino mass. According to ECHo spokesperson Prof. Dr Loredana Gastaldo, a scientist at Heidelberg University’s Kirchhoff Institute for Physics, the current results verify that even larger-scale investigations will be feasible in future to get even closer to the mass of neutrinos and ultimately precisely determine it.

Neutrinos are elementary particles with extremely low mass that have no electrical charge. Because their interaction with matter is very weak, the properties of these “ghost particles” are very difficult to determine. This is especially true for the neutrino mass, which has yet to be precisely measured, with only its upper limit being known. According to Loredana Gastaldo, determining the mass could pave the way for new theoretical models beyond the standard model of particle physics and thereby contribute to a better understanding of the evolution of our universe.

Several research groups worldwide are trying to determine the neutrino mass scale through the analysis of radioactive decays. The thus far smallest upper value has been obtained by the “Karlsruhe Tritium Neutrino Experiment” (KATRIN), which is, however, approaching its final sensitivity, as Prof. Gastaldo explains. The ECHo experiment has been designed to complement the KATRIN results and eventually reach an even better sensitivity. The collaboration, for which the scientist has served as spokesperson since 2011, includes research teams from Heidelberg, Mainz, Darmstadt, Tübingen, and Karlsruhe, as well as Geneva (Switzerland) and Grenoble (France).

As part of the ECHo experiments to determine the neutrino mass, the researchers are studying the energy released during the decay of Holmium-163. In this decay process, a proton in the atomic nucleus of this radioactive isotope captures an electron. The interaction between these two particles produces a neutron and a “ghost-like” neutrino, which is ejected with a specific energy. The mass of the neutrino causes a slight change in the energy distribution of the atomic excitations. “We can draw conclusions about the mass of the neutrino from the slight changes in the measured energy spectrum,” states Prof. Gastaldo. According to the experimental physicist, the isotope Holmium-163 is especially well suited for these measurements, because very little energy is released during its decay. That means that even tiny fluctuations in the spectral shape can be proven with appropriate detectors.

Metallic magnetic calorimeters are used for the ECHo experiments. These detectors were developed and built at the Kirchhoff Institute for Physics under the direction of Prof. Gastaldo. They are approximately 200 micrometers in size and operated at extremely low temperatures of 20 millikelvins, so that even the tiniest energy differences in the form of temperature fluctuations are evident. The Holmium-163 is embedded directly in the detectors at the RISIKO facility of Johannes Gutenberg University Mainz. Thanks to an improved detector design, approximately 200 million such Holmium-163 decay processes were observed for the first time during the latest experiment carried out at Heidelberg University.

This allowed the researchers to adjust downward the mass upper limit by approximately one order of magnitude compared to previous ECHo measurements – and by a factor two compared to the results of the HOLMES Collaboration, which also uses Holmium-163 to determine the neutrino mass. “This result reinforces the significance of the ECHo experiments and demonstrates that even larger-scale experiments using Holmium-163 will be possible in future,” stresses Loredana Gastaldo. To this end, she plans to increase the number of detectors from the current 100 to 20,000. For the “Electron Capture in Ho-163 – Large Experiment” (ECHo-LE) project, she has obtained an ERC Advanced Grant from the European Research Council (ERC).

Teams from Heidelberg University, the Max-Planck Institute for Nuclear Physics in Heidelberg, Johannes Gutenberg University Mainz, the Helmholtz Institute Mainz, the GSI Helmholtz Centre for Heavy Ion Research in Darmstadt, the University of Tübingen, and the Karlsruhe Institute of Technology have all contributed to the current research. Other contributors include researchers from the CERN European research center in Geneva (Switzerland) and the Institut Laue-Langevin in Grenoble (France). The German Research Foundation funded the work. The results were published in the journal “Physical Review Letters”.

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Journal

Physical Review Letters

DOI

10.1103/lqkb-hylx 

Article Title

Improved Limit on the Effective Electron Neutrino Mass with the ECHo-1k Experiment

Article Publication Date

25-Mar-2026

WAIT, WHAT?!

CERN's most delicate road trip: Scientists take antimatter out of the lab for the first time

By Theo Farrant & AP

Published on 25/03/2026 - EURONEWS

Housed in a high-tech, super-cooled container, the fragile particles survived a short truck journey without touching normal matter, which would have made them vanish in a flash of energy.

One short truck ride, one giant leap for particle physics.

Scientists have taken antimatter, some of the universe’s rarest particles, out of the lab and onto the road for the first time - in a carefully controlled truck experiment that could transform how it is studied.

At the CERN Antimatter Factory near Geneva, researchers carefully transported around 100 antiprotons by truck in a specially designed container, in a four-hour experiment aimed at proving they can be moved safely.

Antimatter is notoriously fragile. If antiprotons come into contact with normal matter - even for a fraction of a second - they annihilate, releasing energy.

To prevent this, the antiprotons have been encased in a roughly 1-metre-cube box, known as a “transportable antiproton trap,” that uses special magnets cooled to -269 degrees Celsius (-452 Fahrenheit) and allows the antiprotons to be suspended in a vacuum – not touch the inner walls, which are made of... matter.

The half-hour drive tested whether the particles could remain contained outside the controlled lab environment.

Why is it important to be able to move antimatter?

So why all the fuss over antimatter? It holds answers to one of science’s biggest mysteries: why the universe exists in its current form, said particle physicist Professor Tara Shears from the University of Liverpool, who is not involved in the project,

"Antimatter is one of the biggest mysteries that we have in science. It's very rare to start with, so we haven't been able to study it very much.

"But it holds the keys to our understanding of what literally why the universe is like it is because the whole issue for us is that when the universe is started out life, half of it was made of antimatter," said Shears.

A truck carries the transportable antimatter trap during a road test at the European Organization for Nuclear Research (CERN), in Meyrin near Geneva, Switzerland. Credit: AP Photo

The experiment is a first step toward transporting antiprotons to specialised labs elsewhere in Europe - such as Heinrich Heine University in Düsseldorf, which is about eight hours away in normal driving conditions - for precise measurements. But doing this is no easy feat.

'The moment these antimatter protons come into contact with normal matter, they annihilate each other. They just vanish in a puff of light," said professor Alan Barr, from the University of Oxford.

He said the key challenge in this experiment is stopping that from happening.

"The technology traps antimatter protons in an ultra-cold vacuum, suspended by powerful electric and magnetic fields. It literally keeps them from touching the sides of the container. This transport is a proof of principle. It shows that, in the future, we can do these moves routinely and study antimatter in detail," Barr said.

He said in pushing yourself to do these very hard things, "you’re forced to invent technologies that end up being used elsewhere. That’s not why we’re doing this, but it’s what happens as a side effect."

What breakthroughs could come from this development?

Shears said CERN has begun a long journey to scientific discovery and we can't imagine now what benefits it could unfold for humanity in future.

"I am sure that had (will have) applications elsewhere. I just can't tell you what it is at the moment because we haven't thought about it yet. But we will," she said.

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.

Work remains: The trap has a maximum of four hours of autonomy now, and the drive to Düsseldorf is twice that.

New particle discovered by Large Hadron Collider


By AFP
March 17, 2026


Physicists using the Large Hadron Collider have discovered a new particle - Copyright AFP/File VALENTIN FLAURAUD

The Large Hadron Collider has discovered a new particle, the 80th identified so far by the world’s most powerful particle smasher, Europe’s CERN physics laboratory announced Tuesday.

The new particle has been named “Xi-cc-plus”. Scientists hope the particle — which is similar to a proton but four times heavier — will reveal more about the strange behaviour of quantum mechanics.

All the matter around us — including the protons and neutrons that make up the nucleus of atoms — are made of baryons.

These common particles are composed of three quarks, which are fundamental building blocks of matter.

Quarks come in six “flavours”: up, down, charm, strange, top and bottom. Each has varying mass, electric charge and quantum properties.

In theory, there could be many different types of baryons that mix these flavours — however most are extremely difficult to observe.

To chase them down, the Large Hadron Collider sends particles whizzing around an underground ring at phenomenal speeds until they smash into each other.

This gives scientists a brief chance to measure how the more stable elements decay, then deduce the properties of the original particle.

The newly discovered “Xi-cc-plus” contains two “charm” quarks and one “down” quark.

Normal protons have two “up” quarks and one “down” quark. Because the new particle has two heavier “charm” quarks instead of “up” ones, it has a much greater mass.

Vincenzo Vagnoni, spokesman for the Large Hadron Collider beauty (LHCb) experiment, said it was “only the second time a baryon with two heavy quarks has been observed”.

It is also “the first new particle identified after the upgrades to the LHCb detector that were completed in 2023,” he said in a statement.

“The result will help theorists test models of quantum chromodynamics, the theory of the strong force that binds quarks into not only conventional baryons and mesons but also more exotic hadrons such as tetraquarks and pentaquarks.”

In 2017, the LHCb experiment announced that it had discovered a similar particle, made of two “charmed” quarks and one “up” quark.

The new particle has an expected lifetime six times shorter than this earlier one, making it far more tricky to spot, CERN said.

The Large Hadron Collider is a 27-kilometre (17 mile) long proton-smashing ring running about 100 metres below France and Switzerland. Mostly famously, it proved the existence of the Higgs boson — known as the “God particle” — in 2012.

The latest discovery comes as CERN plans to build an even bigger particle smasher, the Future Circular Collider, to continue probing the mysteries of the universe.