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Category: particle physics – Page 53

Calculating the electron’s magnetic moment: State-dependent values emerge from Dirac equation

Quantum mechanics has a reputation that precedes it. Virtually everyone who has bumped up against the quantum realm, whether in a physics class, in the lab, or in popular science writing, is left thinking something like, “Now, that is really weird.” For some, this translates to weird and wonderful. For others it is more like weird and disturbing.

Chip Sebens, a professor of philosophy at Caltech who asks foundational questions about physics, is firmly in the latter camp. “Philosophers of physics generally get really frustrated when people just say, ‘OK, here’s quantum mechanics. It’s going to be weird. Don’t worry. You can make the right predictions with it. You don’t need to try to make too much sense out of it, just learn to use it.’ That kind of thing drives me up the wall,” Sebens says.

One particularly weird and disturbing area of physics for people like Sebens is theory. Quantum field theory goes beyond quantum mechanics, incorporating the and allowing the number of particles to change over time (such as when an electron and positron annihilate each other and create two photons).

Studies offer new insights into production and structure of heavy hollow atoms

Hollow atoms are special atoms with multiple missing electrons in their inner shells, while their outer shells are still fully or partially filled with electrons. Studying the production mechanisms, internal structure, and de-excitation properties of these excited-state atoms provides insights into quantum electrodynamics and quantum many-body interactions, with applications in fields such as inner-shell ionization X-ray lasers, high-energy density physics, and molecular imaging.

Researchers at the Institute of Modern Physics (IMP) of the Chinese Academy of Sciences recently confirmed that the fully stripped heavy ion-atom collision is an effective way to produce heavy hollow atoms in high yield. They have also developed a high-resolution planar crystal to measure the fine structure of inner-shell multi-ionization ion X-rays.

The results have been published in Spectrochimica Acta Part B: Atomic Spectroscopy and Physical Review A.

Stoichiometric crystal shows promise in quantum memory

For over two decades, physicists have been working toward implementing quantum light storage—also known as quantum memory—in various matter systems. These techniques allow for the controlled and reversible mapping of light particles called photons onto long-lived states of matter. But storing light for long periods without compromising its retrieval efficiency is a difficult task.

Nuclear mass measurement reveals new proton magic number

In nuclear physics, “magic numbers” identify specific numbers of protons or neutrons that lead to especially stable nuclei. Recognizing these numbers helps scientists better understand the structure of nuclei.

The for stable, long-lived isotopes have long been known, but the magic numbers for exotic, short-lived isotopes are less well understood. By studying these rare cases, researchers can gain deeper insight into the nuclear “building code” under extreme conditions. This, in turn, improves our understanding of how elements formed in the universe and sheds light on the behavior of the nuclear force.

As part of this effort, researchers from the Institute of Modern Physics (IMP) of the Chinese Academy of Sciences have precisely measured for the first time the mass of an extremely short-lived and neutron-deficient nucleus, silicon-22, revealing that the number 14 in silicon-22 is a new magic number.

New particle acceleration strategy uses cold atoms to unlock cosmic mysteries

Scientists have used ultracold atoms to successfully demonstrate a novel method of particle acceleration that could unlock a new understanding of how cosmic rays behave, a new study reveals.

More than 70 years after its formulation, researchers have observed the Fermi acceleration mechanism in a laboratory by colliding against engineered movable potential barriers—delivering a significant milestone in high-energy astrophysics and beyond.

Fermi acceleration is the mechanism responsible for the generation of cosmic rays, as postulated by physicist Enrico Fermi in 1949. The process itself also features some universal properties that have spawned a wide range of mathematical models, such as the Fermi-Ulam model. Until now, however, it has been difficult to create a reliable Fermi accelerator on Earth.

Elusive romance of top-quark pairs observed at Large Hadron Collider

An unforeseen feature in proton-proton collisions previously observed by the CMS experiment at CERN’s Large Hadron Collider (LHC) has now been confirmed by its sister experiment ATLAS.

The result, reported yesterday at the European Physical Society’s High-Energy Physics conference in Marseille, suggests that —the heaviest and shortest-lived of all the elementary particles—can momentarily pair up with their antimatter counterparts to produce a “quasi-bound-state” called toponium. Further input based on complex theoretical calculations of the strong nuclear force—called (QCD)—will enable physicists to understand the true nature of this elusive dance.

High-energy collisions between protons at the LHC routinely produce top quark–antiquark pairs. Measuring the probability, or cross section, of this process is both an important test of the Standard Model of particle physics and a powerful way to search for the existence of new particles that are not described by the theory.

Pretrained jet foundation model successfully utilized for tau reconstruction

Simulating data in particle physics is expensive and not perfectly accurate. To get around this, researchers are now exploring the use of foundation models—large AI models trained in a general, task-agnostic way on large amounts of data.

Just like how language models can be pretrained on the full dataset of internet text before being fine-tuned for specific tasks, these models can learn from large datasets of particle jets, even without labels.

After the pretraining, they can be fine-tuned to solve specific problems using much less data than traditional approaches.

Elusive romance of top-quark pairs observed at the LHC

An unforeseen feature in proton-proton collisions previously observed by the CMS experiment at CERN’s Large Hadron Collider (LHC) has now been confirmed by its sister experiment ATLAS. The result, reported yesterday at the European Physical Society’s High-Energy Physics conference in Marseille, suggests that top quarks – the heaviest and shortest-lived of all the elementary particles – can momentarily pair up with their antimatter counterparts to produce a “quasi-bound-state” called toponium. Further input based on complex theoretical calculations of the strong nuclear force — called quantum chromodynamics (QCD) — will enable physicists to understand the true nature of this elusive dance.

High-energy collisions between protons at the LHC routinely produce top quark–antiquark pairs. Measuring the probability, or cross section, of this process is both an important test of the Standard Model of particle physics and a powerful way to search for the existence of new particles that are not described by the theory.

Last year, CMS researchers were analysing a large sample of top quark–antiquark production data collected from 2016 to 2018 to search for new types of Higgs bosons when they observed something unusual. The team saw a surplus of top quark–antiquark pairs, which is often considered as a smoking gun for the presence of new particles. Intriguingly, the excess appeared at the very minimum energy required to produce such a pair of top quarks. This led the team to consider an alternative hypothesis of something that had long been considered too difficult to detect at the LHC: a short-lived union of a top quark and a top antiquark.

An approach to realize heralded photon storage in a Rydberg superatom

Quantum technologies, systems that operate leveraging quantum mechanical effects, have the potential to outperform classical technologies in some specific tasks. Over the past decades, some researchers have also been trying to realize quantum networks, systems comprised of multiple connected quantum devices.

So far, have been the most widely used particles for carrying across different devices in quantum networks. The main reasons for this are that photons can travel at remarkable speeds, while weakly interacting with their surrounding environment, which helps to preserve the quantum states they are carrying.

To successfully employ photons in quantum networks, however, physicists and engineers need to be able to confirm that they are stored successfully without destroying them.

Hydrogen atom transfer method selectively transforms carboxylic acids using an inexpensive photocatalyst

Carboxylic acids are ubiquitous in bioactive organic molecules and readily available chemical building blocks. Carboxylic acids can be converted into carboxy radicals that can initiate versatile carbon–carbon and carbon–heteroatom bond formations, which are highly desirable for developing materials and pharmaceuticals. Currently, however, there are few applicable methods that use inexpensive catalysts.

To this end, researchers from WPI-ICReDD and University of Shizuoka have developed a facile hydrogen atom transfer (HAT) method that selectively transforms into carboxy radicals using xanthone, an inexpensive commercial organic ketone photocatalyst. This research was published in the Journal of the American Chemical Society.

HAT converts substrates into radical species by removing a hydrogen atom and ketones are highly accessible, inexpensive, and known for HAT photocatalysis. However, selective HAT for carboxylic acids is challenging because the O–H bond is stronger than adjacent C–H bonds. Nonetheless, using the artificial force–induced reaction (AFIR) method, a developed at ICReDD, the authors identified xanthone as a promising ketone photocatalyst for selective O–H bond HAT.

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