Physics News and Discussions

[weatheriscool]

PandaX sets new constraints on the search for light dark matter via ionization signals
https://phys.org/news/2023-07-pandax-co ... ation.html
by Ingrid Fadelli , Phys.org

Teams of physicists worldwide have been trying to detect dark matter, an elusive type of matter that does not emit, absorb, or reflect light. Due to its lack of interactions with electromagnetic forces, this matter is very difficult to observe directly, thus most researchers are instead searching for signals originating from its interactions with other particles in its surroundings.

The PandaX experiment is a research effort dedicated to the search of dark matter using data collected by the Particle and Astrophysical xenon detector, situated at the China Jinping Underground Laboratory (CJPL) in Sichuan, in China. In a recent paper published in Physical Review Letters, the researchers involved in this large-scale experiment published the results of their most recent search for light dark matter (i.e., weakly interacting massive particles with masses below 1 GeV).

[weatheriscool]

ATLAS sets record precision on Higgs boson's mass
https://phys.org/news/2023-07-atlas-pre ... -mass.html
by CERN

In the 11 years since its discovery at the Large Hadron Collider (LHC), the Higgs boson has become a central avenue for shedding light on the fundamental structure of the universe. Precise measurements of the properties of this special particle are among the most powerful tools physicists have to test the Standard Model, currently the theory that best describes the world of particles and their interactions. At the Lepton Photon Conference this week, the ATLAS collaboration reported how it has measured the mass of the Higgs boson more precisely than ever before.

The mass of the Higgs boson is not predicted by the Standard Model and must therefore be determined by experimental measurement. Its value governs the strengths of the interactions of the Higgs boson with the other elementary particles as well as with itself. A precise knowledge of this fundamental parameter is key to accurate theoretical calculations which, in turn, allow physicists to confront their measurements of the Higgs boson's properties with predictions from the Standard Model. Deviations from these predictions would signal the presence of new or unaccounted-for phenomena. The Higgs boson's mass is also a crucial parameter driving the evolution and the stability of the universe's vacuum.

The ATLAS and CMS collaborations have been making ever more precise measurements of the Higgs boson's mass since the particle's discovery. The new ATLAS measurement combines two results: a new Higgs boson mass measurement based on an analysis of the particle's decay into two high-energy photons (the "diphoton channel") and an earlier mass measurement based on a study of its decay into four leptons (the "four-lepton channel").

[weatheriscool]

Physicists achieve breakthrough in Monte Carlo computer simulations
https://phys.org/news/2023-07-physicist ... tions.html
by Leipzig University

Researchers at Leipzig University have developed a highly efficient method to investigate systems with long-range interactions that were previously puzzling to experts. These systems can be gases or even solid materials such as magnets whose atoms interact not only with their neighbors but also far beyond.

Professor Wolfhard Janke and his team of researchers use Monte Carlo computer simulations for this purpose. This stochastic process, named after the Monte Carlo casino, generates random system states from which the desired properties of the system can be determined. In this way, Monte Carlo simulations provide deep insights into the physics of phase transitions.

The researchers have developed a new algorithm that can perform these simulations in a matter of days, which would have taken centuries using conventional methods. They have published their new findings in the journal Physical Review X.

[weatheriscool]

New radar research overcomes nearly century-old trade-off between wavelength and distance resolution
https://phys.org/news/2023-08-radar-cen ... tance.html
by Chapman University

New interference radar functions employed by a team of researchers from Chapman University and other institutions improve the distance resolution between objects using radar waves. The results may have important ramifications in military, construction, archaeology, mineralogy and many other domains of radar applications.

This first proof-of-principle experiment opens a new area of research with many possible applications that can be disruptive to the multi-billion dollar radar industry. There are many new avenues to pursue both in theory and experiment.

The discovery addresses a nine decades-old problem that requires scientists and engineers to sacrifice detail and resolution for observation distance—underwater, underground, and in the air. The previous bound limited the distance estimated between objects to be one quarter of the wavelength of radio waves; this technology improves the distance resolution between objects using radar waves.

"We believe this work will open a host of new applications as well as improve existing technologies," says John Howell, the lead author of the article published today in Physical Review Letters. "The possibility of efficient humanitarian demining or performing high-resolution, non-invasive medical sensing is very motivating," he adds.

Howell and a team of researchers from the Institute for Quantum Studies at Chapman University, the Hebrew University of Jerusalem, the University of Rochester, the Perimeter Institute and the University of Waterloo have demonstrated range resolution more than 100 times better than the long-believed limit. This result breaks the trade-off between resolution and wavelength, allowing operators to use long wavelengths and now have high spatial resolution.

[weatheriscool]

Scientists observe first evidence of 'quantum superchemistry' in the laboratory

by Louise Lerner, University of Chicago
https://phys.org/news/2023-08-scientist ... atory.html

A team from the University of Chicago has announced the first evidence for "quantum superchemistry"—a phenomenon where particles in the same quantum state undergo collective accelerated reactions. The effect had been predicted, but never observed in the laboratory.

The findings, published July 24 in Nature Physics, open the door to a new field. Scientists are intensely interested in what are known as "quantum-enhanced" chemical reactions, which could have applications in quantum chemistry, quantum computing, and other technologies, as well as in better understanding the laws of the universe.

"What we saw lined up with the theoretical predictions," said Cheng Chin, a professor of physics and member of the James Franck Institute and Enrico Fermi Institute, whose lab conducted the research. "This has been a scientific goal for 20 years, so it's a very exciting era."

[weatheriscool]

Demon hunting: Physicists confirm 67-year-old prediction of massless, neutral composite particle
https://phys.org/news/2023-08-demon-phy ... utral.html
by Michael O'Boyle, University of Illinois Grainger College of Engineering

In 1956, theoretical physicist David Pines predicted that electrons in a solid can do something strange. While they normally have a mass and an electric charge, Pines asserted that they can combine to form a composite particle that is massless, neutral, and does not interact with light. He called this particle a "demon." Since then, it has been speculated to play an important role in the behaviors of a wide variety of metals. Unfortunately, the same properties that make it interesting have allowed it to elude detection since its prediction.

Now, a team of researchers led by Peter Abbamonte, a professor of physics at the University of Illinois Urbana-Champaign, have finally found Pines' demon 67 years after it was predicted. As the researchers report in the journal Nature, they used a nonstandard experimental technique that directly excites a material's electronic modes, allowing them to see the demon's signature in the metal strontium ruthenate.

[weatheriscool]

Scientists may be on brink of discovering fifth force of nature
Experts closing in on potentially identifying new force after surprise wobble of subatomic particle

Fri 11 Aug 2023 08.01 EDT

The tantalising theory that a fifth force of nature could exist has been given a boost thanks to unexpected wobbling by a subatomic particle, physicists have revealed.

According to current understanding, there are four fundamental forces in nature, three of which – the electromagnetic force and the strong and weak nuclear forces – are explained by the standard model of particle physics.

However, the model does not explain the other known fundamental force, gravity, or dark matter – a strange and mysterious substance thought to make up about 27% of the universe.

Now researchers have said there could be another, fifth, fundamental force of nature.

More: https://www.theguardian.com/science/202 ... rce-nature

[weatheriscool]

Switching 'spin' on and off (and up and down) in quantum materials at room temperature
https://phys.org/news/2023-08-quantum-m ... ature.html
by University of Cambridge

Researchers have found a way to control the interaction of light and quantum 'spin' in organic semiconductors, that works even at room temperature.

Spin is the term for the intrinsic angular momentum of electrons, which is referred to as up or down. Using the up/down spin states of electrons instead of the 0 and 1 in conventional computer logic could transform the way in which computers process information. And sensors based on quantum principles could vastly improve our abilities to measure and study the world around us.

An international team of researchers, led by the University of Cambridge, has found a way to use particles of light as a 'switch' that can connect and control the spin of electrons, making them behave like tiny magnets that could be used for quantum applications.

The researchers designed modular molecular units connected by tiny 'bridges.' Shining a light on these bridges allowed electrons on opposite ends of the structure to connect to each other by aligning their spin states. Even after the bridge was removed, the electrons stayed connected through their aligned spins.

[weatheriscool]

Research group detects a quantum entanglement wave for the first time using real-space measurements
https://phys.org/news/2023-08-group-qua ... space.html
by Aalto University

Triplons are tricky little things. Experimentally, they're exceedingly difficult to observe. And even then, researchers usually conduct the tests on macroscopic materials, in which measurements are expressed as an average across the whole sample.

That's where designer quantum materials offer a unique advantage, says Academy Research Fellow Robert Drost, the first author of a paper published in Physical Review Letters. These designer quantum materials let researchers create phenomena not found in natural compounds, ultimately enabling the realization of exotic quantum excitations.

"These materials are very complex. They give you very exciting physics, but the most exotic ones are also challenging to find and study. So, we are trying a different approach here by building an artificial material using individual components," says Professor Peter Liljeroth, head of the Atomic Scale physics research group at Aalto University.

Quantum materials are governed by the interactions between electrons at the microscopic level. These electronic correlations lead to unusual phenomena like high-temperature superconductivity or complex magnetic states, and quantum correlations give rise to new electronic states.

[weatheriscool]

New experimental research measures the speed of molecular charge migration for the first time
https://phys.org/news/2023-08-experimen ... ation.html
by SPIE

To discover how light interacts with molecules, the first step is to follow electron dynamics, which evolve at the attosecond timescale. The dynamics of this first step have been called charge migration (CM). CM plays a fundamental role in chemical reactions and biological functions associated with light–matter interaction. For years, visualizing CM at the natural timescale of electrons has been a formidable challenge in ultrafast science due to the ultrafine spatial (angstrom) and ultrafast temporal (attosecond) resolution required.

Experimentally, the sensitive dependence of CM on molecular orbitals and orientations has made the CM dynamics complex and difficult to trace. There are still some open questions about molecular CM that remain unclear. One of the most fundamental questions: how fast does the charge migrate in molecules? Although molecular CM has been extensively studied theoretically in the last decade by using time-dependent quantum chemistry packages, a real measurement of the CM speed has remained unattainable, due to the extreme challenge.

As reported in Advanced Photonics, a research team from Huazhong University of Science and Technology (HUST), in cooperation with theoretical teams from Kansas State University and University of Connecticut, recently proposed a high harmonic spectroscopy (HHS) method for measuring the CM speed in a carbon-chain molecule, butadiyne (C4H2).