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Category: particle physics

Neutrinos Make a Break in the Ice

The spectrum of cosmic neutrinos can unmask the types of astrophysical sources that produce these and other high-energy particles. The IceCube Neutrino Observatory, whose detectors lie buried in Antarctic ice, has been measuring cosmic neutrinos since 2010. Early data releases suggested that the neutrino spectrum is a single falling power law, which is consistent with simple models relating cosmic neutrinos to cosmic rays. But now, after 14 years of observation, IceCube’s data show evidence for a break, or knee-like downward bend, in the spectrum at an energy of around 30 tera-electron-volts [1, 2]. Such a break could evince a mix of neutrino sources.

Cosmic neutrinos are predominantly generated whenever high-energy cosmic rays collide with other particles. The neutrino spectrum can therefore reveal information about how and where cosmic rays are accelerated. If the acceleration takes place exclusively in shock environments, where collisions produce neutrinos, the neutrino spectrum would be a single power law. However, the latest analysis of neutrino data by the IceCube Collaboration has uncovered a more complex spectrum. The researchers sifted through a decade’s worth of neutrino observations using improved models of both backgrounds and detector uncertainties. The results show a spectrum break with a statistical confidence of 4 sigma (where 5 sigma constitutes a bona fide detection).

The break could mean that neutrinos come from more than one source class, with each class having a different way of accelerating cosmic rays, says collaboration member Vedant Basu from the University of Utah. He also points out that the observed shape of the neutrino spectrum is consistent with predictions based on the properties of the diffuse gamma-ray background, supporting models that assume the two types of particles originate from the same sources.

Quantum experiment shows events may have no fixed order

For the first time, a team of physicists in Austria has carried out an experiment that appears to verify the principle of indefinite causal order: an idea that suggests that timelines of events can exist in multiple orders at the same time. Led by Carla Richter at the Vienna Center for Quantum Science and Technology, the researchers hope their result could finally allow physicists to verify a key prediction of quantum theory. The results have been published in PRX Quantum.

The basic principle of cause and effect underpins everything that happens in the classical world: for an event to occur, it must be triggered by another event in its past. Yet in the quantum world, physicists have long suspected that these rules may not always apply.

Just as quantum particles can exist in superpositions of multiple states which collapse to a single outcome when measured, indefinite causal order suggests something similar may apply to entire sequences of events. Until a measurement is made, multiple orders of cause and effect can exist in superposition.

Experimental evidence shows how photons spread across multiple paths in an interferometer

The nature of quantum particles has long puzzled scientists. While single-particle interference suggests that a photon can behave like a spread-out wave, a whole photon is only ever detected in one specific place. Traditional interpretations of quantum mechanics often address this by suggesting the particle is in a superposition of being here and there at the same time. However, this tells us only where the particle is when it is measured, not where the particle physically is when no detector is present.

A research team led by Hiroshima University, led by Holger F. Hofmann, professor at the Graduate School of Advanced Science and Engineering, has now developed a method to measure this delocalization without disturbing the photon’s wave-like path.

In a study published in the New Journal of Physics, the researchers applied a modification of the well-established method of “weak measurements” to a two-path interferometer. As the photon traveled, they applied a tiny rotation by a positive angle in one path and a negative angle in the other. If the two paths interfere in the output, the average rotation angle is always zero. However, this is only a statistical average.

‘Near-misses’ in particle accelerators can illuminate new physics, study finds

Particle accelerators reveal the heart of nuclear matter by smashing together atoms at close to the speed of light. The high-energy collisions produce a shower of subatomic fragments that scientists can then study to reconstruct the core building blocks of matter.

An MIT-led team has now used the world’s most powerful particle accelerator to discover new properties of matter, through particles’ “near-misses.” The approach has turned the particle accelerator into a new kind of microscope—and led to the discovery of new behavior in the forces that hold matter together.

In a study appearing this week in the journal Physical Review Letters, the team reports results from the Large Hadron Collider (LHC)—a massive underground, ring-shaped accelerator in Geneva, Switzerland. Rather than focus on the accelerator’s particle collisions, the MIT team searched for instances when particles barely glanced by each other.

Hearing research traces evolution of key inner ear protein

In the intricate machinery of the inner ear, hearing begins with a protein that moves a few billionths of a meter up to 100,000 times per second. That protein, called TMC1, sits at the tips of sensory hair cells deep in the snail-shaped cochlea. When sound waves move these microscopic hairs, TMC1 acts as a channel, opening and allowing charged particles to flow into the cell and trigger an electrical signal to the brain.

Without TMC1, that signal never starts. Mutations in the TMC1 gene are a well-known cause of hereditary hearing loss in humans. Because of this central role, TMC1 is an attractive target for researchers designing gene therapies aimed at restoring hearing. Several groups are testing ways to supply working copies of the gene or fix harmful mutations.

For these efforts to be safe and effective, scientists need to know in detail how TMC1 is built, how it opens, and which parts of the protein are most sensitive to change. However, the hair-cell system that includes TMC1 is so complex, sensitive, and hard to access that it is notoriously difficult to take apart and study directly.

‘Cool’ detectors cut neutrino mass upper limit by an order of magnitude

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. The study is published in the journal Physical Review Letters.

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 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.

Dust-resilient perovskite solar cells could cut manufacturing costs and expand green energy worldwide

Research appearing in Communications Materials has shown that perovskite solar cells (PSCs) are remarkably resilient to dust during production, challenging the industry belief that high-performance solar technology must be manufactured in sterile and expensive cleanrooms. This discovery could reduce the need for ultra-clean factories, making solar cell production cheaper and more accessible worldwide.

PSCs are a new type of technology that uses a unique crystal structure to harvest light. They are thinner, lighter, and potentially much cheaper to produce than the traditional silicon panels found on roofs today. However, traditional silicon cells are incredibly fragile during the making process; even a single microscopic dust particle can ruin a cell. This forces manufacturers to use expensive, energy-hungry cleanrooms, creating a massive barrier to production in developing nations.

Researchers at Swansea University’s Faculty of Science & Engineering have now found that perovskite technology has a unique tolerance to common dust and debris.

Now you see it, now you don’t: Material can transition between quantum states

A team of scientists led by the U.S. Department of Energy’s (DOE) Argonne National Laboratory has identified a rare, switchable quantum property in a new type of nickel sulfide material. The discovery could have applications in high-speed transistors, adaptive sensors and other devices that require a material’s electronic structure to be controlled on the fly. The research is published in the journal Matter.

The compound, KxNi4S2 (0 ≤ x ≤ 1), contains nickel and sulfur sandwiched between layers of potassium. The “(0 ≤ x ≤ 1)” in the name means that the amount of potassium in the material can vary from no potassium at all to a full potassium atom, depending on the sample.

First detailed in a 2021 paper, it was created as part of an ongoing quest to develop more superconductors. As researchers examined the layered material’s characteristics, they happened upon a remarkable feature: applying an electrical current could drive the potassium layers out, collapsing the sandwich and changing the material’s structure.

New ultra-fast particle detector could help unmask dark matter

The CMS experiment at CERN is building a new detector that will unravel the chaotic particle collisions at the Large Hadron Collider, helping scientists identify particles based on their speeds.

What if Olympic officials could record sprinters’ times only to the nearest minute? “We would know who started the race, and who finished the race, but that’s it,” said Bryan Cardwell, a postdoctoral researcher at the University of Virginia. “There’s no way to know who arrived first and who arrived last.”

Cardwell and his colleagues on the CMS experiment are currently tackling a similar problem. The CMS experiment records the tracks and properties of subatomic particles created by the Large Hadron Collider, the world’s most powerful particle accelerator. As it stands, physicists get a picture of all the particles produced in a collision, but they have insufficiently detailed information about when the particles were produced or how fast they were traveling, making it difficult to tell them apart.

Microsoft-backed start-up raises $40 million for helium atom beam lithography that could print chips at atomic resolution — 0.1nm beam is 135 times narrower than ASML’s EUV light

Lace Lithography, a Norwegian start-up backed by Microsoft, raised $40 million in Series A funding on Monday to develop a chipmaking tool that uses a helium atom beam instead of light to pattern silicon wafers, Reuters reported. The company claims its technology can create chip features 10 times smaller than current lithography systems, with a beam width of just 0.1 nanometers compared to the 13.5nm wavelength used by ASML’s EUV scanners. Lace aims to have a test tool running in a pilot fab by 2029.

The advantage of Lace’s system is that atoms don’t have a diffraction limit, whereas photon-based lithography, including ASML’s EUV systems, is constrained by the wavelength of the light it uses. As chipmakers push features smaller, they rely on increasingly complex multi-patterning techniques to work around that limit, but Lace sidesteps the problem entirely by replacing photons with neutral helium atoms and a beam measuring roughly the width of a single hydrogen atom.

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