Physics News and Discussions

weatheriscool
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Physicists confirm hitch in proton structure
https://phys.org/news/2022-10-physicist ... roton.html
by Thomas Jefferson National Accelerator Facility

Nuclear physicists have confirmed that the current description of proton structure isn't all smooth sailing. A new precision measurement of the proton's electric polarizability performed at the U.S. Department of Energy's Thomas Jefferson National Accelerator Facility has revealed a bump in the data in probes of the proton's structure.

Though widely thought to be a fluke when seen in earlier measurements, this new, more precise measurement has confirmed the presence of the anomaly and raises questions about its origin. The research has just been published in the journal Nature.

According to Ruonan Li, first author on the new paper and a graduate student at Temple University, measurements of the proton's electric polarizability reveal how susceptible the proton is to deformation, or stretching, in an electric field. Like size or charge, the electric polarizability is a fundamental property of proton structure.

What's more, a precision determination of the proton's electric polarizability can help bridge the different descriptions of the proton. Depending on how it is probed, a proton may appear as an opaque single particle or as a composite particle made of three quarks held together by the strong force.

"We want to understand the substructure of the proton. And we can imagine it like a model with the three balanced quarks in the middle," Li explained. "Now, put the proton in the electric field. The quarks have positive or negative charges. They will move in opposite directions. So, the electric polarizability reflects how easily the proton will be distorted by the electric field."
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Anomalous magnetic moment of the muon—a new conundrum comes to light
https://phys.org/news/2022-10-anomalous ... ndrum.html
by Universitaet Mainz
The anomalous magnetic moment of the muon is a crucial parameter in particle physics as it allows for precision tests of the established Standard Model. A new measurement of this quantity last year caused something of a furor as it reaffirmed a significant deviation from the theoretical prediction—in other words, the anomalous magnetic moment is greater than anticipated.

Physicists calculate the theoretical prediction on the basis of the currently valid Standard Model of particle physics. In 2020, the Muon g-2 Theory Initiative—a group of 130 physicists with a strong representation from Mainz—produced a consensual estimate that has since been accepted as the reference value. Since then, several teams—including that of Prof. Hartmut Wittig of the PRISMA+ Cluster of Excellence at Johannes Gutenberg University Mainz (JGU)—have published new results for the contribution from the strong interaction using numerical simulations of lattice QCD, which suggest that the theoretical prediction is moving towards the experimental value.

"Even if it turns out that the deviation between the theoretical and experiment results is actually smaller than we thought, this would still represent a major divergence," explains Hartmut Wittig. "But it is still imperative for us to first understand why the use of differing theoretical methods leads to such dissimilar results."
weatheriscool
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Researchers create first quasiparticle Bose-Einstein condensate
https://phys.org/news/2022-10-quasipart ... nsate.html
by University of Tokyo
Physicists have created the first Bose-Einstein condensate—the mysterious fifth state of matter—made from quasiparticles, entities that do not count as elementary particles but that can still have elementary-particle properties like charge and spin. For decades, it was unknown whether they could undergo Bose-Einstein condensation in the same way as real particles, and it now appears that they can. The finding is set to have a significant impact on the development of quantum technologies including quantum computing.

A paper describing the process of creation of the substance, achieved at temperatures a hair's breadth from absolute zero, was published in the journal Nature Communications.

Bose-Einstein condensates are sometimes described as the fifth state of matter, alongside solids, liquids, gases and plasmas. Theoretically predicted in the early 20th century, Bose-Einstein condensates, or BECs, were only created in a lab as recently as 1995. They are also perhaps the oddest state of matter, with a great deal about them remaining unknown to science.

BECs occur when a group of atoms is cooled to within billionths of a degree above absolute zero. Researchers commonly use lasers and magnet traps to steadily reduce the temperature of a gas, typically composed of rubidium atoms. At this ultracool temperature, the atoms barely move and begin to exhibit very strange behavior.

They experience the same quantum state—almost like coherent photons in a laser—and start to clump together, occupying the same volume as one indistinguishable super atom. The collection of atoms essentially behaves as a single particle.
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Light-analyzing 'lab on a chip' opens door to widespread use of portable spectrometers
https://phys.org/news/2022-10-light-ana ... pread.html
by Oregon State University
Scientists including an Oregon State University materials researcher have developed a better tool to measure light, contributing to a field known as optical spectrometry in a way that could improve everything from smartphone cameras to environmental monitoring.

The study, published today in Science, was led by Finland's Aalto University and resulted in a powerful, ultra-tiny spectrometer that fits on a microchip and is operated using artificial intelligence.

The research involved a comparatively new class of super-thin materials known as two-dimensional semiconductors, and the upshot is a proof of concept for a spectrometer that could be readily incorporated into a variety of technologies—including quality inspection platforms, security sensors, biomedical analyzers and space telescopes.

"We've demonstrated a way of building spectrometers that are far more miniature than what is typically used today," said Ethan Minot, a professor of physics in the OSU College of Science. "Spectrometers measure the strength of light at different wavelengths and are super useful in lots of industries and all fields of science for identifying samples and characterizing materials."
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caltrek
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Scientists Just Discovered an Entirely New Way of Measuring Time
by Mike McRae
October 31, 2022

Extract:
(Science Alert) Their (Uppsala University in Sweden) experiments on the wave-like nature of something called a Rydberg state have revealed a novel way to measure time that doesn't require a precise starting point.

Just like actual waves in a pond, having more than one Rydberg wave packet rippling about in a space creates interference, resulting in unique patterns of ripples. Throw enough Rydberg wave packets into the same atomic pond, and those unique patterns will each represent the distinct time it takes for the wave packets to evolve in accordance with one another.

It was these very 'fingerprints' of time that the physicists behind this latest set of experiments set out to test, showing they were consistent and reliable enough to serve as a form of quantum timestamping.

Their research involved measuring the results of laser-excited helium atoms and matching their findings with theoretical predictions to show how their signature results could stand in for a duration of time.

"The benefit of this is that you don't have to start the clock – you just look at the interference structure and say 'okay, it's been 4 nanoseconds.'"
Read more here: https://www.sciencealert.com/scientist ... ring-time
Don't mourn, organize.

-Joe Hill
jiminluv
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The Challenge of Ruling Out Inflation via the Primordial Graviton Background

Image: Image

Reference: https://www.cam.ac.uk/research/news/can ... -ruled-out

There are now ideas for future, direct, observational tests of inflation by attempting to detect signatures of cosmic graviton background (<1 K). Any failure to detect one would confirm CDM, and otherwise is also true.

"Is it possible in principle to test cosmic inflation in a model-independent way?
Sunny Vagnozzi"
weatheriscool
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First-of-its-kind experimental evidence defies conventional theories about how plasmas emit or absorb radiation
https://phys.org/news/2022-11-first-of- ... ional.html
by University of Rochester
Most people are familiar with solids, liquids, and gases as three states of matter. However, a fourth state of matter, called plasmas, is the most abundant form of matter in the universe, found throughout our solar system in the sun and other planetary bodies.

Because dense plasma—a hot soup of atoms with free-moving electrons and ions—typically only forms under extreme pressure and temperatures, scientists are still working to comprehend the fundamentals of this state of matter. Understanding how atoms react under extreme pressure conditions—a field known as high-energy-density physics (HEDP)—gives scientists valuable insights into the fields of planetary science, astrophysics, and fusion energy.

One important question in the field of HEDP is how plasmas emit or absorb radiation. Current models depicting radiation transport in dense plasmas are heavily based on theory rather than experimental evidence.

In a new paper published in Nature Communications, researchers at the University of Rochester Laboratory for Laser Energetics (LLE) used LLE's OMEGA laser to study how radiation travels through dense plasma.
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New technique accurately measures how 2D materials expand when heated


by Adam Zewe, Massachusetts Institute of Technology


https://phys.org/news/2022-11-technique ... rials.html
Two-dimensional materials, which consist of just a single layer of atoms, can be packed together more densely than conventional materials, so they could be used to make transistors, solar cells, LEDs, and other devices that run faster and perform better.

One issue holding back these next-generation electronics is the heat they generate when in use. Conventional electronics typically reach about 80 degrees Celsius, but the materials in 2D devices are packed so densely in such a small area that the devices can become twice as hot. This temperature increase can damage the device.

This problem is compounded by the fact that scientists don't have a good understanding of how 2D materials expand when temperatures rise. Because the materials are so thin and optically transparent, their thermal expansion coefficient (TEC)—the tendency for the material to expand when temperatures increase—is nearly impossible to measure using standard approaches.

"When people measure the thermal expansion coefficient for some bulk material, they use a scientific ruler or a microscope because with a bulk material, you have the sensitivity to measure them. The challenge with a 2D material is that we cannot really see them, so we need to turn to another type of ruler to measure the TEC," says Yang Zhong, a graduate student in mechanical engineering.

Zhong is co-lead author of a research paper that demonstrates just such a "ruler." Rather than directly measuring how the material expands, they use laser light to track vibrations of the atoms that comprise the material. Taking measurements of one 2D material on three different surfaces, or substrates, allows them to accurately extract its thermal expansion coefficient.
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Researchers report new technique to measure the fine structure constant
https://phys.org/news/2022-11-technique ... stant.html
by Vienna University of Technology
The fine structure constant is one of the most important natural constants of all. At TU Wien, a remarkable way of measuring it has been found—it shows up as a rotation angle.

One over 137: This is one of the most important numbers in physics. It is the approximate value of the so-called fine structure constant—a physical quantity that is of outstanding importance in atomic and particle physics.

There are many ways to measure the fine structure constant—usually it is measured indirectly, by measuring other physical quantities and using them to calculate the fine structure constant. At TU Wien, however, an experiment has now been performed, in which the fine structure constant itself can be directly measured—as an angle.

1/137—the secret code of the universe

The fine structure constant describes the strength of the electromagnetic interaction. It indicates how strongly charged particles such as electrons react to electromagnetic fields. If the fine structure constant had a different value, our universe would look completely different—atoms would have a different size, so all chemistry would work differently, and nuclear fusion in the stars would be completely different as well.

A much-discussed question is whether the fine structure constant is actually constant, or whether it could possibly have changed its value a little over billions of years.

Direct measurements instead of calculations

"Most important physical constants have a specific unit—for example, the speed of light, which can be given in the unit of meters per second," says Prof. Andrei Pimenov from the Institute of Solid State Physics at TU Wien. "It's different with the fine structure constant. It has no unit, it is simply a number—it is dimensionless."
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Evidence of Higgs boson contributions to the production of Z boson pairs at high energies
https://phys.org/news/2022-11-evidence- ... ction.html
by Ingrid Fadelli , Phys.org

The Higgs boson, the fundamental subatomic particle associated with the Higgs field, was first discovered in 2012 as part of the ATLAS and CMS experiments, both of which analyze data collected at CERN's Large Hadron Collider (LHC), the most powerful particle accelerator in existence. Since the discovery of the Higgs boson, research teams worldwide have been trying to better understand this unique particle's properties and characteristics.

The CMS Collaboration, the large group of researchers involved in the CMS experiment, has recently obtained an updated measurement of the width of the Higgs boson, while also gathering the first evidence of its off-shell contributions to the production of Z boson pairs. Their findings, published in Nature Physics, are consistent with standard model predictions.

"The quantum theoretical description of fundamental particles is probabilistic in nature, and if you consider all the different states of a collection of particles, their probabilities must always add up to 1 regardless of whether you look at this collection now or sometime later," Ulascan Sarica, researcher for the CMS Collaboration, told Phys.org. "When analyzed mathematically, this simple statement imposes restrictions, the so-called unitarity bounds, on the probabilities of particle interactions at high energies."

Since the 1970s, physicists have predicted that when pairs of heavy vector bosons Z or W are produced, typical restrictions at high energies would be violated, unless a Higgs boson was contributing to the production of these pairs. Over the past ten years, theoretical physics calculations showed that the occurrence of these Higgs boson contributions at high energies should be measurable using existing data collected by the LHC.
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