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Category: particle physics

Cracking a 16-year proton mystery as ultra-precise hydrogen measurements confirm a smaller-than-expected core

The simplicity of a hydrogen atom makes it an ideal model for studying atomic structure and interactions. Yet, despite the fact that its simplest form consists of only one proton and one electron, physicists have had a hard time pinning down the exact charge radius of the proton. But a new study, published in the journal Physical Review Letters, outlines a method of measurement that helps to resolve some past discrepancies.

In the quest to better understand one of the universe’s most important building blocks, several research teams have focused on measuring the proton’s charge radius—a measure of the spatial distribution of electric charge from a proton—using hydrogen spectroscopy. Some research teams did these experiments with normal hydrogen atoms and some with a form of hydrogen called muonic hydrogen. Muonic hydrogen is an exotic hydrogen atom consisting of a negatively charged muon bound to a proton, instead of an electron bound to a proton.

Theoretically, the protons in both regular and muonic hydrogen should have the same proton charge radius. However, some experimental results have shown disagreements regarding the rather precise measurements of muonic hydrogen’s charge radius, which gave a smaller value. This discrepancy is referred to as the “proton radius puzzle,” and it has plagued physicists since 2010, when the first results from a highly precise muonic hydrogen spectroscopy experiment came out.

Protein clusters reshape cell movement and may help cells build amino acids faster

Cells can be thought of as cities, with factories, a transport system, and lots of building activity. An international team led by scientists at the University of Groningen studied cells growing under different conditions and measured the speed of molecule transport. They found that some conditions led to changes in the mobility inside the cells, caused by the clustering of proteins that produce the building materials for growth. It could be that clustering enables the proteins to produce those building blocks more efficiently. The research is published in the journal Molecular Cell.

The research started with a seemingly simple question. How much movement is there within a cell? “We provided bacteria with different nutrients and this resulted in different growth rates,” explains Matthias Heinemann, Professor of Molecular Systems Biology. Movement was measured by inserting tiny (40 nanometers) fluorescent particles in the cells that could be tracked under the microscope. “To our surprise, we found that particle movement under different conditions could vary by a factor of three.”

The scientific literature could not explain this observation. By analyzing the cell content, the scientists found a correlation between movement of the fluorescent particles and the number of proteins that are involved in the production of amino acids. “More of these proteins meant less movement inside the cell,” says Heinemann. “This led us to the question of why this happens. Our hypothesis was that these proteins form clusters that act as obstacles to movement inside the cells.”

A tabletop ring of atoms brings the universe’s doomsday vacuum collapse into the lab

Physicists in China have simulated the effect of “false vacuum decay”: a phenomenon believed to play out constantly in the seemingly empty expanses of space, and which one theory even suggests could bring an abrupt end to the entire universe. In a paper published in Physical Review Letters, Yu-Xin Chao and colleagues at Tsinghua University, Beijing, mimicked the effect using a simple tabletop experiment.

For now, quantum field theory is our most accurate framework for fundamental physics below the scale at which gravity becomes important. It predicts that there is no such thing as a perfect vacuum: while a given space may appear entirely empty, the theory suggests that it is actually just the lowest-energy state of a continuous quantum field.

Since a quantum field can possess multiple local minima energy, this means that a seemingly stable local ground state may not be the most stable state possible for the field as a whole—it is simply separated from a lower-energy, more stable state by an energy barrier, much as a valley may be separated from a deeper valley by a high mountain ridge.

Self-interacting dark matter may solve three cosmic puzzles

A study led by UC Riverside physicist Hai-Bo Yu suggests that a new type of dark matter could explain three astrophysical puzzles across vastly different environments. Published in Physical Review Letters, the study proposes that dense clumps of self-interacting dark matter (SIDM)—each about a million times the mass of the sun—can account for unusual gravitational effects observed in gravitational lenses, stellar streams, and satellite galaxies.

Dark matter, which makes up about 85% of the universe’s matter, cannot be seen directly. The standard model assumes it is “cold” and collisionless, meaning that particles pass through one another without interacting. This model struggles, however, to explain certain high-density structures observed in the universe.

Yu’s work instead focuses on SIDM, in which dark matter particles collide and exchange energy. These interactions can trigger “gravothermal collapse,” forming extremely dense, compact cores.

High-resolution imaging captures cavity-induced density waves in a quantum gas

A new study, published in Physical Review Letters, reports that scientists have successfully imaged the formation of cavity-induced density waves induced by laser light in an ultracold quantum gas. Previously, only global signals, such as photon leakage or the peak in energy deposition of a fast charged particle (Bragg peaks), have been used to detect this kind of ordering. Prior to this study, there had been no direct, high-resolution in situ imaging of cavity-induced density-wave order in ultracold gases.

When laser light is arranged so that it bounces back and forth between two mirrors, light waves become trapped and create what is referred to as an optical cavity. This creates standing waves or amplifies light through resonance. When atoms in an ultracold unitary Fermi gas are placed in an optical cavity, they can absorb and emit this light. Unitary Fermi gases exist in a strongly interacting state where the wave scattering length makes interactions independent of the specific atomic details.

Light emitted by atoms in the gas can be absorbed by other atoms. This exchange of photons creates further interactions between the atoms that can cause a self-rearrangement into a periodic pattern within the gas, referred to as a density wave. This self-organization occurs above a critical threshold, called the superradiant phase transition, where the exchange of photons enables simultaneous, collective interaction among all atoms.

How nuclear batteries could speed the race to fusion power

Fusion reactions release tremendous amounts of energy by fusing two lighter atoms into a heavier one. But harvesting that energy has proven challenging. The most common approach is to heat water and spin a steam turbine, but that approach isn’t terribly efficient, harnessing at best around 60% of the power.

Avalanche Energy thinks it can capture more of that energy by developing new materials known as radiovoltaics. Radiovoltaics are similar to photovoltaics — traditional solar panels — in that they use semiconductors to transform radiation into electricity. They’ve been around for a while, but they’re not very effective. Existing radiovoltaics are easily damaged by the very radiation they harness and don’t produce that much electricity.

Today, Avalanche was awarded a $5.2 million contract from DARPA to develop new radiovoltaics, the company exclusively told TechCrunch.

Gravitational waves may be hidden in the light atoms emit

“Our findings may open a route toward compact gravitational-wave sensing, where the relevant atomic ensemble is millimeter-scale,” said Navdeep Arya, a postdoctoral researcher at Stockholm University. “A thorough noise analysis is necessary to assess practical feasibility, but our first estimates are promising.”

If confirmed, this approach could eventually lead to much smaller and more accessible detectors, offering a new way to observe some of the universe’s most dramatic events.

Universal surface-growth law confirmed in two dimensions after 40 years

Crystals, bacterial colonies, flame fronts: the growth of surfaces was first described in the 1980s by the Kardar–Parisi–Zhang equation. Since then, it has been regarded as a fundamental model in physics, with implications for mathematics, biology, and computer science.

Now—40 years later—a Würzburg-based research team from the Cluster of Excellence ctd.qmat has achieved the first experimental demonstration of KPZ behavior on 2D surfaces in space and time.

This was made possible by sophisticated materials engineering and a bold experimental approach: researchers injected polaritons—hybrid particles composed of light and matter—into the material. The results have been published in Science.

Dual-frequency Paul trap shows potential for synthesizing antihydrogen outside of CERN

A new type of radiofrequency trap can capture particles with extremely different requirements and could theoretically hold both types of particles at the same time. Researchers in the group of Professor Dmitry Budker from the PRISMA++ Cluster of Excellence and the Helmholtz Institute at Johannes Gutenberg University Mainz (JGU) were able to trap calcium ions or electrons in the same apparatus.

The team’s findings, published in Physical Review A, show the potential of this technology for synthesizing antihydrogen.

“Radiofrequency traps, also called Paul traps, have long been used by physicists to trap specific particles,” Dr. Hendrik Bekker explained. “However, they are usually limited to a single frequency.”

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