The combined results add to physicists’ understanding and they validate the impressive collaborative effort
between two competing — yet complementary — experiments.

TORONTO, Oct. 22, 2025 – The (T2K) experiment in Japan and the (NOvA) experiment in the United States, previously considered rival experiments, conducted a joint analysis and published their first results today in the journal .

Both are long-baseline neutrino oscillation experiments using accelerators, and by leveraging their different baselines and neutrino energies, they achieved precision measurements of neutrino oscillations.

Neutrinos are subatomic particles that are neutral and weigh almost nothing, and almost never interact with the matter around them, making them notoriously hard to study. However, they may hold the secret to why the universe is now filled with matter and light. Everything known about particle physics tells scientists that when the universe began there were equal amounts of matter and antimatter, which when they collide, annihilate to form light.

“If matter and antimatter behave identically, then the universe now should hold nothing but light.  Something must have tipped the balance to favour matter over antimatter, and all the other particles we have studied till now cannot tip this balance. It is possible that neutrinos may be what tipped that balance, so the field is trying as hard as it can to see if neutrinos and antineutrinos behave differently from each other,” says 91��ɫ Professor Deborah Harris.

Harris, a particle physicist in the Department of Physics and Astronomy, Faculty of Science, is an active member of the large research collaboration T2K.  She also collaborates on a next generation neutrino oscillation experiment aiming to measure oscillations with even more precision, called the Deep Underground Neutrino Experiment (DUNE), and is a senior scientist at Fermi National Accelerator Laboratory in the United States. 

The combined efforts of T2K and NOvA succeeded in reducing the uncertainty in the differences between neutrino masses to below two per cent. Although the ordering of the three neutrino masses is still unknown, their results show that depending on this ordering, the magnitude of CP symmetry violation – a difference in behaviour between particles and antiparticles – would be strongly constrained.

This achievement marks an important step toward uncovering CP symmetry violation in neutrinos and the origin of the matter–antimatter asymmetry in the universe. The joint analysis combined 10 years of T2K data collected since 2010 and six years of NOvA data collected since 2014, and it also demonstrates the strength of collaboration between two international experiments that are competitive yet complementary.

“This combination does not yet see a definitive difference between neutrinos and antineutrinos but by combining the two experiment’s data we know much more about neutrinos than either experiment can tell us by itself,” says Harris.

91��ɫ researchers have been an important part of T2K since its inception and contributed the critical Optical Transition Radiation Detector in the beamline. These researchers include Professor Sampa Bhadra and postdoctoral Fellows Dr. Noë Roy and Dr. Arturo Fiorentini, and former PhD students Dr. Rowan Zaki and Dr. Mitchell Yu.    

Context

When the universe began, physicists expect there should have been equal amounts of matter and antimatter. But if that were so, the matter and antimatter should have perfectly canceled each other out, resulting in total annihilation.

And yet, here we are. Somehow, matter won out over antimatter — but we still don’t know how or why.

Physicists suspect the answer may lie in the mysterious behaviour of abundant yet elusive particles called neutrinos. Specifically, learning more about a phenomenon called neutrino oscillation — in which neutrinos change types, or flavours, as they travel — could bring us closer to an answer.

The international collaborations representing two neutrino experiments, T2K in Japan and NOvA in the United States, recently combined forces to produce their first joint results, published today in the journal Nature. This initial joint analysis provides some of the most precise neutrino-oscillation measurements in the field.

“These results are an outcome of a cooperation and mutual understanding of two unique collaborations, both involving many experts in neutrino physics, detection technologies and analysis techniques, working in very different environments, using different methods and tools,” says T2K collaborator Tomáš Nosek.

Different experiments, common goals

Despite their ubiquity, neutrinos are very difficult to detect and study. Even though they were first seen in the 1950s, the ghostly particles remain deeply enigmatic. Filling in gaps in our knowledge about neutrinos and their properties may reveal fundamental truths about the universe.

T2K and NOvA are both long-baseline experiments: they each shoot an intense beam of neutrinos that passes through both a near detector close to the neutrino source and a far detector hundreds of miles away. Both experiments compare data recorded in each detector to learn about neutrinos’ behaviour and properties.

NOvA, the NuMI Off-axis ν_e Appearance experiment, sends a beam of neutrinos 810 kilometers from its source at the U.S. Department of Energy’s Fermi National Accelerator Laboratory near Chicago, Ill., to a 14,000-ton liquid-scintillator detector in Ash River, Minnesota.

The T2K experiment’s neutrino beam travels 295 kilometers from Tokai to Kamioka — hence the name T2K. Tokai is home to the Japan Proton Accelerator Research Complex (J-PARC) and Kamioka hosts the Super-Kamiokande neutrino detector, an enormous tank of ultrapure water located a kilometer underground.

Since the experiments have similar science goals but different baselines and different neutrino energies, physicists can learn more by combining their data.

“By making a joint analysis you can get a more precise measurement than each experiment can produce alone,” says NOvA collaborator Liudmila Kolupaeva. “As a rule, experiments in high-energy physics have different designs even if they have the same science goal. Joint analyses allow us to use complementary features of these designs.”

As long-baseline experiments, NOvA and T2K are ideal for studying neutrino oscillations, a phenomenon that can provide insight into open questions like charge-parity violation and the neutrino mass ordering. Two experiments with different baselines and energies have a better chance of disentangling the two effects than one experiment alone.

Interrogating neutrino oscillations

The mystery of neutrino mass ordering is the question of which neutrino is the lightest. But it isn’t as simple as placing particles on a scale. Neutrinos have miniscule masses that are made up of combinations of mass states. There are three neutrino mass states, but, confusingly, they don’t map to the three neutrino flavours. In fact, each flavour is made of a mix of the three mass states, and each mass state has a different probability of acting like each flavour of neutrino.

There are two possible mass orderings, called normal or inverted. Under the normal ordering, two of the mass states are relatively light and one is heavy, while the inverted ordering has two heavier mass states and one light.

In the normal ordering, there is an enhanced probability that muon neutrinos will oscillate to electron neutrinos but a lower probability that muon antineutrinos will oscillate to electron antineutrinos. In the inverted ordering, the opposite happens. However, an asymmetry in the neutrinos’ and antineutrinos’ oscillations could also be explained if neutrinos violate CP symmetry — in other words, if neutrinos don’t behave the same as their antimatter counterparts.

The combined results of NOvA and T2K do not favour either mass ordering. If the neutrino mass ordering is found to be normal, NOvA’s and T2K’s results are less clear on CP symmetry, requiring additional data to clarify. However, if future results show the neutrino mass ordering is inverted, the results published today provide evidence that neutrinos violate CP symmetry, potentially explaining why the universe is dominated by matter instead of antimatter.

“Neutrino physics is a strange field. It is very challenging to isolate effects,” says Kendall Mahn, co-spokesperson for T2K. “Combining analyses allows us to isolate one of these effects, and that’s progress.”

The combined analysis does provide one of the most precise values of the difference in mass between neutrino mass states, a quantity called Δm²₃₂. With an uncertainty below two per cent, the new value will enable physicists to make precision comparisons with other neutrino experiments to test whether the neutrino oscillation theory is complete.

What’s next

These first joint results do not definitively solve any mysteries of neutrinos, but they do add to physicists’ knowledge about the particles. Plus, they validate the impressive collaborative effort between two competing — yet complementary — experiments.

The NOvA collaboration consists of more than 250 scientists and engineers from 49 institutions in eight countries. The T2K collaboration has more than 560 members from 75 institutions in 15 countries. The two collaborations began active work on this joint analysis in 2019. It combines six years of data from NOvA, which began collecting data in 2014, and a decade of data from T2K, which started up in 2010.  Both experiments continue to take data, and efforts are already underway to update the joint analysis with the new data.

“The joint analysis work has benefited both collaborations,” says Patricia Vahle, co-spokesperson for NOvA. “We have a much better mutual understanding of the strengths and challenges of the different experimental setups and analysis techniques.”

NOvA and T2K are the only currently operating long-baseline neutrino experiments. Their initial combined results lay a foundation for forthcoming neutrino experiments that will answer the questions around neutrinos unambiguously.

The Fermilab led Deep Underground Neutrino Experiment is under construction in Illinois and South Dakota in the U.S. With its longer baseline of 1,300 kilometers, DUNE will be more sensitive to neutrino mass ordering and could give physicists a conclusive answer shortly after it turns on in the early years of the next decade.

In Japan, Hyper-Kamiokande, the successor to Super-Kamiokande, is currently under construction in an underground mine in Kamioka, Hida City, Gifu Prefecture, with experiments scheduled to begin in 2028. Hyper-Kamiokande will conduct highly sensitive searches for CP symmetry violation through high-statistics measurements made possible by a detector about eight times larger and an intense neutrino beam.

Many physicists hope these next-generation neutrino experiments can come together — as NOvA and T2K have already done — to make progress on their shared scientific goals to learn more about neutrinos and their unusual properties.

“As shown in this very analysis, there are no truly ‘rivaling’ experiments because they all share a common goal of scientific study of a phenomenon,” says Nosek. “Collaborating is naturally important for the transfer of knowledge, know-how and experience, and for sharing resources, ideas and tools. The T2K-NOvA collaboration is not merely a sum of T2K and NOvA collaborations. It is much, much more.”

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New computer simulations follow the formation of galaxies and the cosmic large-scale structure with unprecedented statistical precision

TORONTO, July 19, 2023 – 91��ɫ and an international team of astrophysicists have made an ambitious attempt to simulate the formation of galaxies and cosmic large-scale structure throughout staggeringly large swaths of space. First results of their “MillenniumTNG” project are published in a series of 10 articles in the journal Monthly Notices of the Royal Astronomical Society. The new calculations help to subject the standard cosmological model to precision tests and to unravel the full power of upcoming new cosmological observations, say the researchers including 91��ɫ Assistant Professor Rahul Kannan.

Over the past decades, cosmologists have gotten used to the perplexing conjecture that the universe’s matter content is dominated by enigmatic dark matter and that an even stranger dark energy field that acts as some kind of anti-gravity to accelerate the expansion of today’s cosmos. Ordinary baryonic matter makes up less than five per cent of the cosmic mix, but this source material forms the basis for the stars and planets of galaxies like our own Milky Way.

This seemingly strange cosmological model is known under the name LCDM. It provides a stubbornly successful description of a large number of observational data, ranging from the cosmic microwave radiation – the rest-heat left behind by the hot Big Bang – to the “cosmic web”, where galaxies are arranged along an intricate network of dark matter filaments. However, the real physical nature of dark matter and dark energy is still not understood, prompting astrophysicists to search for cracks in the LCDM theory. Identifying tensions to observational data could lead to a better understanding of these fundamental puzzles about our Universe. Sensitive tests are required that need both: powerful new observational data as well as more detailed predictions about what the LCDM model actually implies.  

An international team of researchers led by the Max Planck Institute for Astrophysics (MPA) in Germany, Harvard University in the US, Durham University in the UK, and the Donostia International Physics Center in Spain, along with 91��ɫ, have now managed to take a decisive step forward on the latter challenge. Building up on their previous successes with the “Millennium” and “IllustrisTNG” projects, they developed a new suite of simulation models dubbed “MillenniumTNG”, which trace the physics of cosmic structure formation with considerably higher statistical accuracy than what was possible with previous calculations.

Large simulations including new physical details

The team utilized the advanced cosmological code GADGET-4, custom-built for this purpose, to compute the largest high-resolution dark matter simulations to date, covering a region nearly 10 billion light-years across. In addition, they employed the moving-mesh hydrodynamical code AREPO to follow the processes of galaxy formation directly, throughout volumes still so large that they can be considered representative for the universe as a whole. Comparing both types of simulations allows a precise assessment of the impact of baryonic processes related to supernova explosions and supermassive black holes on the total matter distribution. An accurate knowledge of this distribution is key for interpreting upcoming observations correctly, such as so-called weak gravitational lensing effects, which respond to matter irrespective of whether it is of dark or baryonic type.

Furthermore, the team included massive neutrinos in their simulations, for the first time in simulations big enough to allow meaningful cosmological mock observations. Previous cosmological simulations had usually omitted them for simplicity, because they make up at most one to two per cent of the dark matter mass, and since their nearly relativistic velocities mostly prevent them from clumping together. Now, however, upcoming cosmological surveys (such as those of the recently launched Euclid satellite of the European Space Agency) will reach a precision allowing a detection of the associated percent-level effects. This raises the tantalizing prospect to constrain the neutrino mass itself, a profound open question in particle physics, so the stakes are high.

For their ground-breaking MillenniumTNG simulations, the researchers made efficient use of two extremely powerful supercomputers, the SuperMUC-NG machine at the Leibniz Supercomputing Center in Garching, and the Cosma8 machine at Durham Universe. More than 120 000 compute cores toiled away for nearly two months at SuperMUC-NG, using computing time awarded by the German Gauss Centre for Supercomputing, to produce the most comprehensive hydrodynamical simulation model to date. MillenniumTNG is tracking the formation of about one hundred million galaxies in a region of the universe around 2400 million light-years across (see Figure 1). This calculation is about 15 times bigger than the previously best is this category, the TNG300 model of the IllustrisTNG project.

Using Cosma8, the team computed an even bigger volume of the universe, filled with more than a trillion dark matter particles and more than 10 billion particles for tracking massive neutrinos (see Figure 2). Even though this simulation did not follow the baryonic matter directly, its galaxy content can be accurately predicted in MillenniumTNG with a semi-analytic model that is calibrated against the full physical calculation of the project. This procedure leads to a detailed distribution of galaxies and matter in a volume that for the first time is large enough to be representative for the universe as a whole, putting comparisons to upcoming observational surveys on a sound statistical basis.

Theoretical predictions for cosmology

The first results of the MillenniumTNG project show a wealth of new theoretical predictions that reinforce the importance of computer simulations in modern cosmology. The team has written and submitted ten introductory scientific papers for the project. Eight of them have just appeared simultaneously in the journal MNRAS, the remaining two are about to follow shortly.

One timely study examines the discovery of a population of very massive galaxies in the young universe with the James Webb Space Telescope. The masses of these galaxies are unexpectedly large just a brief time after the Big Bang, seemingly defying theoretical expectations. Dr. Kannan analyzed the predictions of MillenniumTNG for this early epoch. While the simulations agree with the observations out to redshifts of z=10 (when the universe was less than 500 million years old), he confirmed that, if they hold up, the new results by JWST at even higher redshift conflicts with the simulation predictions.

“Perhaps star formation is much more efficient shortly after the Big Bang than at later times, or maybe massive stars are formed in higher proportions back then, making these galaxies unusually bright”, says Kannan of 91��ɫ’s Faculty of Science.

Another study looked at the shapes of galaxies. Nearby galaxies have the subtle tendency to orient their shapes in similar directions instead of pointing randomly, an effect called “intrinsic galaxy alignments”. This poorly understood effect distorts inferences based on weak gravitational lensing, which creates its own statistical alignment signal. The MillenniumTNG project could for the first-time measure intrinsic alignments with very high signal-to-noise directly from the shapes of the simulated galaxies, out to distances of several hundred million light-years. “Perhaps our determination of the intrinsic alignment of galaxy orientations can help to resolve the current discrepancy between the amplitude of matter clustering inferred from weak lensing and from the cosmic microwave background,” says PhD-student Ana Maria Delgado of Harvard University, first author of this study of the MillenniumTNG team. Using these results, astronomers will be able to correct for this important systematic effect much better.

Other works of the team’s initial analysis focus on the clustering signals of galaxies. For example, MPA PhD student Monica Barrera produced extremely large and highly realistic mock catalogues of galaxies on the past backwards “lightcone” of a fiducial observer (see Figure 3). In this case, galaxies that are more distant are also automatically younger, reflecting the travel time of the light that is reaching our telescopes. Using these virtual observations, she looked at the so-called baryonic acoustic oscillation (BAO) feature (which provides a cosmologically important standard ruler) in the projected two-point correlation function of galaxies. Her results showed, that measuring these BAOs is a fairly tricky endeavour that can be significantly influenced by so-called cosmic variance effects – even when extremely large volumes are studied in observational surveys. While in simulations one can observe the modelled universe from different vantage points to recover the correct statistical ensemble average, this is unfortunately not readily possible for the real Universe. “The MillenniumTNG simulations are so big and contain so many galaxies, more than 1 billion in the biggest calculation, that it was really hard to study them”, says Monica Barrera. “Analysis scripts that work just fine for smaller simulations tend to take forever for MillenniumTNG.”      

Analyzing cosmological data

The flurry of first results from the MillenniumTNG simulations make it clear that they will be of great help to design better strategies for the analysis of upcoming cosmological data. The team’s principal investigator, Professor Volker Springel from MPA argues that “MillenniumTNG combines recent advances in simulating galaxy formation with the field of cosmic large-scale structure, allowing an improved theoretical modelling of the connection of galaxies to the dark matter backbone of the Universe. This may well prove instrumental for progress on key questions in cosmology, such as how the mass of neutrinos can be best constrained with large-scale structure data.” The MillenniumTNG simulations produced more than three Petabytes of simulation data, forming a rich asset for further research that will keep the participating scientists busy for many years to come.

Original scientific publications:

• The MillenniumTNG Project: The galaxy population at z ≥ 8
  R. Kannan, V. Springel, L. Hernquist, R. Pakmor, A. M. Delgado, B. Hadzhiyska, C. Hernández-Aguayo, M. Barrera, F. Ferlito, S. Bose, S. D. M. White, C. Frenk, A. Smith, E. Garaldi
  MNRAS, July 2023 (preprint: )
• The MillenniumTNG Project: High-precision predictions for matter clustering and halo statistics
  C. Hernández-Aguayo, V. Springel, R. Pakmor, M. Barrera, F. Ferlito, S. D. M. White, L. Hernquist, B. Hadzhiyska, A. M. Delgado, R. Kannan, S. Bose, C. Frenk
  MNRAS, July 2023 (preprint: )
• The MillenniumTNG Project: The hydrodynamical full physics simulation and a first look at its galaxy clusters
  R. Pakmor, V. Springel, J. P. Coles, T. Guillet, C. Pfrommer, S. Bose, M. Barrera, A. M. Delgado, F. Ferlito, C. Frenk, B. Hadzhiyska, C. Hernández-Aguayo, L. Hernquist, R. Kannan, S. D. M. White
  MNRAS, July 2023 (preprint: )
• The MillenniumTNG Project: Semi-analytic galaxy formation models on the past lightcone
  M. Barrera, V. Springel, S. White, C. Hernández-Aguayo, L. Hernquist, C. Frenk, R. Pakmor, F. Ferlito, B. Hadzhiyska, A. M. Delgado, R. Kannan, S. Bose
  MNRAS, submitted (preprint: )
• The MillenniumTNG Project: Refining the one-halo model of red and blue galaxies at different redshifts
  B. Hadzhiyska, L. Hernquist, D. Eisenstein, A. M. Delgado, S. Bose, R. Kannan, R. Pakmor, V. Springel, S. Contreras, M. Barrera, F. Ferlito, C. Hernández-Aguayo, S. D. M. White, C. Frenk
  MNRAS, July 2023 (preprint: )
• The MillenniumTNG Project: An improved two-halo model for the galaxy-halo connection of red and blue galaxies
  B. Hadzhiyska, D. Eisenstein, L. Hernquist, R. Pakmor, S. Bose, A. M. Delgado, S. Contreras, R. Kannan, S. D. M. White, V. Springel, C. Frenk, C. Hernández-Aguayo, F. Ferlito, M. Barrera
  MNRAS, July 2023 (preprint: )
• The MillenniumTNG Project: The large-scale clustering of galaxies
  S. Bose, B. Hadzhiyska, M. Barrera, A. M. Delgado, F. Ferlito, C. Frenk, C. Hernández-Aguayo, L. Hernquist, R. Kannan, R. Pakmor, V. Springel, S. D. M. White
  MNRAS, July 2023 (preprint: )
• The MillenniumTNG Project: Inferring cosmology from galaxy clustering with accelerated N-body scaling and subhalo abundance matching
  S. Contreras, R. E. Angulo, V. Springel, S. D. M. White, B. Hadzhiyska, L. Hernquist, R. Pakmor, R. Kannan, C. Hernández-Aguayo, M. Barrera, F. Ferlito, A. M. Delgado, S. Bose, C. Frenk
  MNRAS, July 2023 (preprint: )
• The MillenniumTNG Project: Intrinsic alignments of galaxies and halos
  A. M. Delgado, B. Hadzhiyska, S. Bose, V. Springel, L. Hernquist, M. Barrera, R. Pakmor, F. Ferlito, R. Kannan, C. Hernández-Aguayo, S. D. M. White, C. Frenk
  MNRAS, July 2023 (preprint: )
• The MillenniumTNG Project: The impact of baryons and massive neutrinos on high-resolution weak gravitational lensing convergence maps
  F. Ferlito, V. Springel, C. T. Davies, C. Hernández-Aguayo, R. Pakmor, M. Barrera, S. D. M. White, A. M. Delgado, B. Hadzhiyska, L. Hernquist, R. Kannan, S. Bose, C. Frenk
  MNRAS, submitted (preprint: )

Further Links:

Web site of the MillenniumTNG project

Gauss Centre for Supercomputing

SuperMUC-NG at the Leibniz Supercomputing Centre

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91��ɫ is a modern, multi-campus, urban university located in Toronto, Ontario. Backed by a diverse group of students, faculty, staff, alumni and partners, we bring a uniquely global perspective to help solve societal challenges, drive positive change and prepare our students for success. 91��ɫ's fully bilingual Glendon Campus is home to Southern Ontario's Centre of Excellence for French Language and Bilingual Postsecondary Education. 91��ɫ’s campuses in Costa Rica and India offer students exceptional transnational learning opportunities and innovative programs. Together, we can make things right for our communities, our planet, and our future.

Media Contacts

91��ɫ: Sandra McLean, 91��ɫ Media Relations, 416-272-6317, sandramc@yorku.ca

MPA: Hannelore Hämmerle, +49-89-30000-3980, pr@mpa-garching.mpg.de

Harvard & Smithsonian Center for Astrophysics: +1- 617-721-7371, pr@, https://cfa.harvard.edu

Communications Office contact Durham University: Leighton Kitson, communications.team@durham.ac.uk,

Scientific contact:

Prof. Dr. Volker Springel, Max-Planck Institute for Astrophysics (MPA), +49-89-30000-2195, vspringel@mpa-garching.mpg.de

Figures / Captions:

Figure 1: /news/wp-content/uploads/sites/242/2023/07/figure1-1-scaled.jpg

Projections of gas (top left), dark matter (top right), and stellar light (bottom center) for a slice in the largest hydrodynamical simulation of MillenniumTNG at the present epoch. The slice is about 35 million light-years thick. The projections show the vast physical scales in the simulation from size, about 2400 million light-years across, to an individual spiral galaxy (final round inset) with a radius of ~150 000 light-years. The underlying calculation is presently the largest high-resolution hydrodynamical simulation of galaxy formation, containing more than 160 billion resolution elements. © MPA

Figure 2: /news/wp-content/uploads/sites/242/2023/07/Figure-2.jpg

Comparison of the neutrino (top) and dark matter (bottom) distributions on the past backwards lightcone of a fiducial observer positioned at the centre of the two horizontal stripes. As cosmic expansion slows down the neutrinos at late times (small redshift/distance), they start to weakly cluster around the biggest concentrations of dark matter as shown by a comparison of the zoomed insets. This slightly increases the mass and further growth rate of these largest structures. © MPA

Figure 3: /news/wp-content/uploads/sites/242/2023/07/Figure-3-scaled.jpg

Galaxy distribution on the past backwards lightcone in MillenniumTNG, where the galaxies are predicted with a sophisticated semi-analytic model on top of the dark matter backbone. Galaxies are shown down to Johnson apparent magnitude 𝑅 < 23, in a 180 degrees wide, thin wedge with opening angle 0.24 degrees, out to redshift 𝑧 = 2. The galaxy positions are drawn as circles with comoving coordinates in real space, using red for galaxies with rest frame color index 𝐵−𝑅 > 0.7, and blue otherwise. Real observations of the galaxy positions would additionally be perturbed by small shifts along the line of sight due to the Doppler effects from the galaxies’ motions, an effect that can also be easily included in the models. The two circular insets show nested zooms with diameters of around 1.25 billion light-years and 125 million light-years, and fainter apparent magnitude limits of 𝑅 < 25 and 𝑅 < 28, respectively. © MPA

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Scientists have discovered a new way to investigate the structure of protons using neutrinos, known as ‘ghost particles’

TORONTO, Feb. 1, 2023 – Scientists are that much closer to understanding protons today after using a novel technique involving a high-energy neutrino beam to precisely measure their size, which could change how these kinds of experiments are done and answer many more questions, say researchers from 91��ɫ.

“We need detailed information about protons to answer questions like which neutrinos have more mass than others and whether or not there are differences between neutrinos and their anti-matter partners,” says Tejin Cai, 91��ɫ postdoctoral researcher and lead author of the published today in Nature. “Our work is one step forward in answering the fundamental questions about neutrino physics that are the goal of these big science projects in the near future.”

The research involved a series of experiments with neutrinos, often referred to as “ghost particles,” over nearly a decade. It was part of the international , which studies neutrinos at ).

“While we were studying neutrinos as part of the MINERvA experiment, I realized a technique I was using might be applied to investigate protons,” says Cai, who did the research, involving an international team of scientists, while completing his PhD in the lab of , the Dr. Steven Chu Professor in Physics and the Acting Vice Provost for Academic Affairs at the University of Rochester.

They found that the proton radius as seen by neutrinos is 0.73 femtometres – a quadrillionth of one metre.

“When we proposed MINERvA, we never thought we’d be able to extract measurements from the hydrogen in the detector,” says Professor Deborah Harris, a particle physicist in 91��ɫ’s Faculty of Science, a senior scientist at Fermilab and a co-spokesperson at MINERvA. “Making this work required great performance from the detector, creative analysis from scientists, and years of running the most intense high-energy neutrino beam on the planet.”

That’s the novel part of this experiment. The use of a beam of neutrinos to investigate the structure of protons was once thought impossible. The MINERvA group used a high-power, high-energy particle accelerator, which produces the strongest source of high-energy neutrinos on the planet. This new technique offers scientists a new way of looking at the small components of an atom’s nucleus.

Although neutrinos are one of the most abundant particles in the universe, they are notoriously difficult to detect and study as they don’t have an electrical charge and nearly zero mass. They are often referred to as “ghost particles” because they rarely interact with atoms, but they play a large role helping scientists answer fundamental questions about the universe.

Atoms, and the protons and neutrons that make up an atom’s nucleus, are so small that researchers have a difficult time measuring them directly. Instead, they build a picture of the shape and structure of an atom’s components by bombarding atoms with a beam of high-energy particles. They then measure how far and at what angles the particles bounce off the atom’s components.

For example, if marbles were thrown at a box, they would bounce off it at certain angles, enabling someone to determine where the box was, its size and shape – even if the box was not visible.

“This is a very indirect way of measuring something, but it allows us to relate the structure of an object – in this case, a proton – to how many deflections we see in different angles,” says McFarland.

A new technique

Specifically, the researchers are hoping to use the technique to separate the effects related to neutrino scattering on protons from the effects related to neutrino scattering on atomic nuclei, which are bound collections of protons and neutrons.  

“Our previous methods for predicting neutrino scattering from protons all used theoretical calculations, but this result directly measures that scattering,” says Cai.

McFarland adds, “By using our new measurement to improve our understanding of these nuclear effects, we will better be able to carry out future measurements of neutrino properties.”

What is a neutrino?

Neutrinos are created when atomic nuclei either come together or break apart. The sun is a large source of neutrinos, which are a byproduct of the sun’s nuclear fusion. If you stand in the sunlight, for example, trillions of neutrinos will harmlessly pass through your body every second.

Even though neutrinos are more abundant in the universe than electrons, it is harder for scientists to experimentally harness them in large numbers; neutrinos pass through matter like ghosts, while electrons interact with matter far more frequently.

“Over the course of a year, on average, there would only be interactions between one or two neutrinos out of the trillions that go through your body every second,” says Cai of 91��ɫ’s Faculty of Science. “There’s a huge technical challenge in our experiments in that we have to get enough protons to look at, and we have to figure out how to get enough neutrinos through that big assembly of protons.”

A chemical trick

The researchers solved this problem in part by using a detector containing a target of both hydrogen and carbon atoms. A target of pure hydrogen wouldn’t be sufficiently dense for enough neutrinos to interact with the atoms.

“We’re performing a ‘chemical trick’, so to speak, by binding the hydrogen up into hydrocarbon molecules that make it able to detect sub-atomic particles,” McFarland says.

To isolate only the information from the hydrogen atoms, the researchers then had to subtract the background “noise” from the carbon atoms.

“The hydrogen and carbon are chemically bonded together, so the detector sees interactions on both at once,” Cai says. “I realized that a technique I was using to study interactions on carbon could also be used to see hydrogen all by itself once you subtract the carbon interactions. A big part of our job was subtracting the very large background from neutrinos scattering on the protons in the carbon nucleus.” 

The collective expertise of MINERvA’s scientists and the collaboration within the group was essential in accomplishing the research, says Cai.

“The result of the analysis and the new techniques developed highlight the importance of being creative and collaborative in understanding data. While a lot of the components for the analysis already exist, putting them together in the right way really made a difference, and this cannot be done without experts with different technical backgrounds sharing their knowledge to make the experiment a success.”

The paper, , is published today in the journal Nature.

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TORONTO, Wednesday, April 15, 2020 – Why is there an abundance of matter compared to antimatter in the Universe? This question has stymied physicists for years, but researchers at 91��ɫ, along with other Canadian institutions as part of the international Tokai-to-Kamioka (T2K) Collaboration, have found neutrinos may hold the answer.

The international is aimed at unraveling this matter-antimatter conundrum by studying neutrinos, subatomic particles produced in huge numbers immediately after the Big Bang. They come in three types – electron, muon, and tau neutrinos – and are created in stars, inside the earth, the atmosphere and at accelerators, such as J-PARC in Japan, where the T2K experiment is conducted.

To tackle this puzzle, the T2K team, including 91��ɫ Faculty of Science physics Professor , the project leader for the optical transition radiation (OTR) detector for the experiment, was looking for behavioural differences of neutrinos (matter) and antineutrinos (antimatter) as they change states during flight into electron neutrinos and electron antineutrinos, respectively.

If matter and antimatter exhibit the same behaviour, charge-parity symmetry implies that the laws of physics are the same for matter and antimatter. But this doesn’t appear to always hold true. For example, there is way more matter than antimatter in the Universe. To account for the observed level of asymmetry, researchers believe there must have been a violation of charge-parity symmetry in the early Universe initiated by neutrinos.

T2K team found the strongest indication yet of this violation in charge-parity symmetry between neutrinos and antineutrinos, but more work is needed to definitively prove it.

The results, published in the journal today, are a major step forward in the study of what caused the original difference between matter and antimatter.

"Neutrino transformations are a beautiful way to study the matter-antimatter asymmetry in the Universe," says Bhadra, who is also a TRIUMF affiliate scientist. "What can be more exciting than studying a particle that may hold the clue to our very existence?"

The T2K experiment used a beam consisting primarily of muon neutrinos or muon antineutrinos created using the proton beam from the in Tokai, Japan.  A small fraction of the neutrinos (or antineutrinos) are detected 295 km away at the Super-Kamiokande water Cerenkov detector in Kamioka, Japan. Previously, T2K studied how the original neutrinos (antineutrinos) transition or oscillate into electron neutrinos (antineutrinos) as they traverse the distance from Tokai to Kamioka (hence the name T2K) in a process called “neutrino oscillations.” This was the subject of the Nobel Prize in Physics in 2015.

The T2K collaboration consists of close to 500 scientists from 12 countries, including Canada. The Canadian effort provided some of the most challenging and critical detectors of the project – the time projection chamber, the fine-grained calorimeter and an OTR detector – and contributed to the success of T2K through key leadership roles.

“Canadian scientists look forward to building on the success of the T2K experiment to realize even more precise measurements of neutrino oscillations through upgrades of the experimental apparatus,” said TRIUMF Professor Mark Hartz, the corresponding author on the paper, former research associate at 91��ɫ, and leader of the Canadian-led Intermediate Water Cerenkov Detector project.

Bhadra says, “91��ɫ will continue to be involved in neutrino physics with more sensitive neutrino experiments being built in the future that will surely provide an answer to the question: what happened to the antimatter?”

Photo of Professor Sampa Bhadra:

Photo of Cover of Nature:

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91��ɫ champions new ways of thinking that drive teaching and research excellence. Our students receive the education they need to create big ideas that make an impact on the world. Meaningful and sometimes unexpected careers result from cross-disciplinary programming, innovative course design and diverse experiential learning opportunities. 91��ɫ students and graduates push limits, achieve goals and find solutions to the world’s most pressing social challenges, empowered by a strong community that opens minds. 91��ɫ U is an internationally recognized research university – our 11 faculties and 25 research centres have partnerships with 200+ leading universities worldwide. Located in Toronto, 91��ɫ is the third largest university in Canada, with a strong community of 53,000 students, 7,000 faculty and administrative staff, and more than 300,000 alumni. 91��ɫ U's fully bilingual Glendon Campus is home to Southern Ontario's Centre of Excellence for French Language and Bilingual Postsecondary Education.

Media Contact:

Sandra McLean, 91��ɫ Media Relations, 416-272-6317, sandramc@yorku.ca

Find out more about how 91��ɫ is creating positive change in the COVID-19 pandemic .

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From left, Dean of 91��ɫ U's Faculty of Science Ray Jayawardhana, President and Vice-Chancellor of 91��ɫ U Rhonda Lenton and Nigel Lockyer, Director of Fermilab

TORONTO, October 17, 2017 – Neutrinos are tiny, abundant particles of matter that pass unnoticed through us and almost always through the Earth, but the full extent of their role in the universe remains a mystery. Neutrinos may hold the key to fundamental questions about the nature of matter, exploding stars and cosmic evolution.

Today, 91��ɫ took a significant step to strengthen its involvement in the next great neutrino physics experiment, being hosted by the United States and under construction, with a view to deciphering the elusive properties of these ubiquitous particles.

The Faculty of Science at 91��ɫ and the Fermi National Accelerator Laboratory (Fermilab) announced an agreement to jointly appoint a scientist who will participate in the (DUNE). It is the first such agreement Fermilab has signed for the experiment with a university outside the United States, and 91��ɫ is the only Canadian university currently involved in the international DUNE collaboration spanning 31 countries.

From left, Dean of 91��ɫ U's Faculty of Science Ray Jayawardhana, President and Vice-Chancellor of 91��ɫ U Rhonda Lenton and Nigel Lockyer, Director of Fermilab

“This landmark agreement with Fermilab is a wonderful reflection of 91��ɫ’s and the Faculty of Science’s commitment to world-class, groundbreaking research,” said Rhonda Lenton, President and Vice-Chancellor of 91��ɫ. “It will provide exciting opportunities for our researchers and students to make a global impact.”

“We are delighted to partner with Fermilab and to have 91��ɫ scientists involved in one of the most exciting and ambitious new ventures in the world of physics,” said Ray Jayawardhana, Dean of the Faculty of Science and author of the popular science book Neutrino Hunters. “Neutrinos play a starring role from the subatomic realm to the cosmic scale, so pinning down their characteristics will help scientists address fundamental questions.”

Nigel Lockyer, Director of Fermilab, said “Fermilab is pleased that 91��ɫU and Canada are joining the international community to build the world’s most ambitious neutrino detector and to measure the properties of this enigmatic particle.”

The newly recruited researcher will be based in the Department of Physics and Astronomy in the Faculty of Science at 91��ɫ, where scientists already collaborate on large, multi-national particle physics projects like the T2K neutrino experiment in Japan and the ATLAS and the ALPHA experiments at the European Organization for Nuclear Research (CERN) in Switzerland.

DUNE is expected to make transformative discoveries that will deepen scientific understanding of neutrinos and their role in the universe, the dynamics of the supernovae that produced the heavy elements necessary for life, and the possibility of proton decay.

The experiment involves more than 1,020 scientists and the excavation of 800,000 tons of rock to build the Long-Baseline Neutrino Facility (LBNF) required for this experiment. LBNF will comprise the world's most intense neutrino beam and include two detectors installed at Fermilab near Chicago and 1,300 km away at the Sanford Underground Research Facility in Lead, South Dakota. Groundbreaking for the experiment took place last July, and prototype detectors are under construction at CERN.

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 is known for championing new ways of thinking that drive teaching and research excellence. Our students receive the education they need to create big ideas that make an impact on the world. Meaningful and sometimes unexpected careers result from cross-discipline programming, innovative course design and diverse experiential learning opportunities. 91��ɫ students and graduates push limits, achieve goals and find solutions to the world’s most pressing social challenges, empowered by a strong community that opens minds. 91��ɫ U is an internationally recognized research university – our 11 faculties and 26 research centres have partnerships with 200+ leading universities worldwide. Located in Toronto, 91��ɫ is the third largest university in Canada, with a strong community of 53,000 students, 7,000 faculty and administrative staff, and more than 295,000 alumni. 91��ɫ U's fully bilingual Glendon campus is home to Southern Ontario's Centre of Excellence for French Language and Bilingual Postsecondary Education.

Media Contact:

Sandra McLean, 91��ɫ Media Relations, 647-654-9452, sandramc@yorku.ca

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TORONTO, Wednesday, July 19, 2017 – 91��ɫ physics Professor Scott Menary is the only Canadian on an experiment, involving 30 countries and the excavation of 800,000 tons of rocks, to find out what role neutrinos played in the evolution of the Universe. The groundbreaking to build the particle detectors for the experiment will take place Friday in the United States.

Neutrinos are tiny, abundant particles of matter that seemingly pass through everything on Earth, but their role in the development of the Universe is still a mystery. A team of 1,000 scientists and engineers from more than 160 institutions, including 91��ɫ, will be part of the new international Deep Underground Neutrino Experiment (DUNE). The plan is to build two particle detectors placed in the world’s most intense neutrino beam. One detector at Fermilab in Illinois will record particles interactions near the source of the beam, the other will do so about a mile underground at Sanford Lab in Lead, South Dakota.

The detectors are expected to take a decade to construct. Neutrinos will then be sent 1,300 kilometres through the Earth from Chicago to the South Dakota detector to shed light on what these mysterious particles do.

The groundbreaking for the initiative will take place simultaneously at both facilities on Friday, July 21.

Faculty of Science expert in antimatter and experimental particle physics, Scott Menary, as the only Canadian on the team, is available to answer questions about the experiment and what scientists are hoping to find.

DUNE and LBNF image gallery for media: 

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91��ɫ is known for championing new ways of thinking that drive teaching and research excellence. Our students receive the education they need to create big ideas that make an impact on the world. Meaningful and sometimes unexpected careers result from cross-discipline programming, innovative course design and diverse experiential learning opportunities. 91��ɫ students and graduates push limits, achieve goals and find solutions to the world’s most pressing social challenges, empowered by a strong community that opens minds. 91��ɫ U is an internationally recognized research university – our 11 faculties and 26 research centres have partnerships with 200+ leading universities worldwide. Located in Toronto, 91��ɫ is the third largest university in Canada, with a strong community of 53,000 students, 7,000 faculty and administrative staff, and more than 295,000 alumni. 91��ɫ U's fully bilingual Glendon campus is home to Southern Ontario's Centre of Excellence for French Language and Bilingual Postsecondary Education.

Media Contact:

Sandra McLean, 91��ɫ Media Relations, 416-736-2100 ext. 22097, sandramc@yorku.ca

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