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Category: particle physics

Experiment indicates new type of mesic nuclei that could reveal how matter acquires mass

Nearly every object we interact with in our lives has a mass, but where does this mass come from? Modern physics says matter acquires its mass from interaction with a physical vacuum—it is not an empty space, but contains a complex structure. Investigating the system of a meson—a composite particle made of a quark, an elementary particle, and its anti-matter, anti-quark—bound to an atomic nucleus, a mesic nucleus, provides precious insight into the vacuum structure, or mass generation mechanism. Scientists are now one step closer to further understanding the origin of mass thanks to new experimental results on a completely new type of mesic nucleus.

The researchers, as part of a major international collaboration, have reported evidence hinting at the existence of a never-before-seen but predicted exotic bound state known as an η′-mesic nucleus. The findings are published in Physical Review Letters.

Physicists have theorized that under certain conditions, short-lived particles called mesons—which only exist for less than a ten-millionth of a second—can become temporarily trapped inside a nucleus, forming an exotic bound system. Measuring mesic nuclei could help scientists understand how the strong nuclear force, which binds atomic nuclei together, behaves and how the vacuum structure changes in extremely high-density environments.

Watching Atoms Make Waves

A new microscope captures how atoms rearrange themselves when they are illuminated inside an optical cavity.

When light hits an atom, it exerts a force on the atom. As weak as these light-induced forces may be, understanding them allows scientists to levitate particles, create the coldest atomic gases in the Universe, operate solar sails, and observe gravitational waves. More exotic phenomena occur when light is confined between a pair of mirrors known as an optical cavity. When a gas of atoms is placed inside such a cavity, light emitted by one atom can be absorbed by another atom. Through the exchange of photons, each atom simultaneously tugs on all the other atoms, causing the ensemble to autonomously rearrange itself into a periodic pattern called a density wave. Now Jean-Philippe Brantut and his colleagues at the Swiss Federal Institute of Technology in Lausanne (EPFL) have built a microscope to, for the first time, image this light-induced density wave in an ultracold atomic gas [1].

Quantum ground state of rotation achieved for the first time in two dimensions

Quantum mechanics tells us that a particle can never be perfectly still. But how precisely can it be oriented? A research team at the University of Vienna, together with colleagues at TU Wien and Ulm University, has now cooled the rotational motion of a levitated silica nanorotor all the way to its quantum ground state—in two orientational degrees of freedom.

Reporting in Nature Physics, they show how optical cooling confines the nanoparticle’s orientation to within the bounds of quantum zero-point fluctuations, the unavoidable orientational uncertainty imposed by Heisenberg’s uncertainty principle. Such quantum-limited alignment is an important milestone towards rotational matter-wave interferometry and ultra-sensitive quantum torque sensing.

Electrons in moiré crystals explore higher-dimensional quantum worlds

The electrons that power our society flow left and right through the circuitry in our electronics, back and forth along the transmission lines that make up our power grid, and up and down to light up every floor of every building. But the electrons in newly discovered “moiré crystals” move in much stranger ways. They can move left and right, back and forth, or up and down in our three-dimensional world, but these electrons also act as if they can teleport in and out of a mysterious fourth dimension of space that is perpendicular to our perceivable reality. Physicists have found that this strange, newly discovered quantum behavior has nothing to do with the electrons themselves and everything to do with the strange material environment in which they live.

The electrons in moiré crystals leap into a fourth dimension through a process called “quantum tunneling.” While a soccer ball sitting at the bottom of a hill will stay put until someone retrieves it, a quantum particle in a valley can jump out all on its own. Quantum tunneling may seem magical to us, but it is quite commonplace in the microscopic quantum world, on the length scales of atoms. Quantum tunneling is also important on larger length scales, particularly in large superconducting circuits that underlie an emerging landscape of quantum technology, as recognized by the 2025 Nobel Prize in Physics.

However, quantum tunneling in moiré crystals is different, in that once an electron tunnels, physicists have now measured that it acts as if it had tunneled into a completely different world and come back again, as if it had been transported through a fourth “synthetic” dimension.

MXene breakthrough boosts conductivity 160x with perfect atomic order

A new technique known as the GLS method takes a very different approach. Instead of relying on harsh chemicals, it starts with solid materials called MAX phases and uses molten salts along with iodine vapor to form MXene sheets. This process allows researchers to control which halogen atoms, including chlorine, bromine, or iodine, attach to the surface.

The result is a much cleaner material. The surface atoms are arranged in a uniform and highly ordered way, and unwanted impurities are greatly reduced. The team demonstrated the versatility of this approach by successfully producing MXenes from eight different MAX phases.

Ytterbium atomic clock could open a new window on fundamental physics

For the first time, an international team of physicists has successfully harnessed a rare orbital transition in atoms of ytterbium to create a new type of atomic clock that is both highly precise and extremely sensitive to fundamental physical effects. Publishing their results in Nature Photonics, the researchers, led by Taiki Ishiyama at Kyoto University, say their approach could pave the way for some of the most stringent tests yet of predictions made by the Standard Model.

To measure the passing of time, an atomic clock excites an electron in confined atoms to a higher energy level, then interrogates the transition frequency of the atoms. Because these oscillations display such little variation, atomic clocks are the most accurate timekeepers ever developed.

To date, the most precise devices involve atoms trapped in an optical lattice: a periodic array of light and darkness created by interfering laser beams. These clocks operate at optical frequencies with hundreds of trillions of oscillations per second—far surpassing the microwave frequencies used in previous atomic clock designs. Already, this extraordinary precision has enabled sensitive tests of fundamental physics, as described by the Standard Model.

Gravity from positivity: Single massive spin-3/2 particle makes gravity logically inevitable, study claims

Researchers at IPhT (CEA, CNRS) and the Universitat Autònoma de Barcelona have shown that gravity—and with it, supersymmetry—emerge as logical necessities whenever a massive spin-3/2 particle exists in nature. Two principles are enough: causality, the fact that no signal can travel faster than light, and unitarity, the requirement that probabilities are conserved in quantum mechanics. The structure of supergravity is not assumed: it bootstraps itself.

In fundamental physics, gravity is usually thought of as an ingredient one adds to a theory. But could it instead be forced by the internal consistency of the quantum world? This is what a study published in the Journal of High Energy Physics demonstrates.

The starting point is disarmingly simple: a single massive spin-3/2 particle. The authors show that such a particle simply cannot exist in isolation within a consistent theory. Its scattering amplitudes grow too fast with energy, clashing with positivity inequalities—the mathematical encoding of causality (the speed of light as an absolute limit) and unitarity (the conservation of probabilities in every quantum process). The theory breaks down barely above the particle’s own mass.

Underground lab clears crucial hurdle for dark matter hunt

Australia’s bid to detect elusive dark matter has taken a major step forward, with new research confirming that cosmic radiation levels deep inside the Stawell Underground Physics Laboratory (SUPL) are low enough to support the world-class experiment that will commence later this year.

ARC Center of Excellence for Dark Matter Particle Physics researchers recorded muon —or cosmic radiation—levels inside and outside the laboratory for more than a year. They detected 30,000 muons inside the underground laboratory, while 8.4 billion muons would be expected to be detected on the surface of Earth.

The SABRE Collaboration paper, published in Astroparticle Physics, is the first to use data collected in SUPL, marking a major achievement for Australian and international scientists involved in the project.

The secrets of black holes and the Higgs mass could be hidden in a 7-dimensional geometry

One of the greatest mysteries of modern physics, the “black hole information paradox,” might have finally found an elegant solution, and the answer could also reveal the origins of the mass of fundamental particles.

In the 1970s, Stephen Hawking demonstrated, through semi-classical calculations, that black holes are not truly black, but emit a weak radiation that causes them to gradually shrink until they disappear.

This process, however, brings with it a massive problem: it seems to cause an irreversible loss of information, violating the unitarity principle of quantum mechanics. In other words, the laws of quantum physics state that information cannot be destroyed, but the evaporation of a black hole suggests otherwise.

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