Physics News and Discussions

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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."

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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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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

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The Challenge of Ruling Out Inflation via the Primordial Graviton Background

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"

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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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First lead-ion collisions in the Large Hadron Collider at record energy
https://phys.org/news/2022-11-lead-ion- ... lider.html
by CERN

On Friday, November 18, a test using collisions of lead ions was carried out in the Large Hadron Collider (LHC) and provided an opportunity for the experiments to validate the new detectors and new data-processing systems ahead of next year's lead-lead physics run.

After the successful start of Run 3 in July this year, which featured proton-proton collisions at the record energy of 13.6 TeV, it was the turn of lead nuclei to circulate in the LHC again last Friday after a gap of four years. Lead nuclei comprise 208 nucleons (protons and neutrons) and are used at the LHC to study quark-gluon plasma (QGP), a state of matter in which the elementary constituents, quarks and gluons, are not confined within nucleons but can move and interact over a much larger volume.

In the test carried out last Friday, lead nuclei were accelerated and collided at a record energy of 5.36 TeV per nucleon-nucleon collision. This is an important milestone in preparation for the physics runs with lead-lead collisions that are planned for 2023 and the following years of Run 3 and Run 4. In lead-lead collisions, each of the 208 nucleons of one of the lead nuclei can interact with one or several nucleons of the other lead nucleus.

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Studying muonium to reveal new physics beyond the Standard Model
https://phys.org/news/2022-11-muonium-r ... ndard.html
by Miriam Arrell, Paul Scherrer Institute

By studying an exotic atom called muonium, researchers are hoping misbehaving muons will spill the beans on the Standard Model of particle physics. To make muonium, they use the most intense continuous beam of low energy muons in the world at Paul Scherrer Institute PSI. The research is published in Nature Communications.

The muon is often described as the electron's heavy cousin. A more appropriate description might be its rogue relation. Since its discovery triggered the words "who ordered that" (Isidor Isaac Rabi, Nobel laureate), the muon has been bamboozling scientists with its law-breaking antics.

The muon's most famous misdemeanor is to wobble slightly too much in a magnetic field: its anomalous magnetic moment hit the headlines with the 2021 muon g-2 experiment at Fermilab. The muon also notably caused trouble when it was used to measure the radius of the proton—giving rise to a wildly different value to previous measurements and what became known as the proton radius puzzle.

Yet rather than being chastised, the muon is cherished for its surprising behavior, which makes it a likely candidate to reveal new physics beyond the Standard Model.

Aiming to make sense of the muon's strange behavior, researchers from PSI and ETH Zurich turned to an exotic atom known as muonium. Formed from a positive muon orbited by an electron, muonium is similar to hydrogen but much simpler. Whereas hydrogen's proton is made up of quarks, muonium's positive muon has no substructure. And this means it provides a very clean model system from which to sort these problems out: for example, by obtaining extremely precise values of fundamental constants such as the mass of the muon.

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Particle physics in a humble glass chip: How quantum optics illuminates the nature of the quark

by Kirstin Werner, University of Rostock
https://phys.org/news/2022-12-particle- ... -chip.html

Scientists from the University of Rostock, Germany were able to recreate fundamental physical properties from the realm of elementary particle physics in a photonic system. The results are published in Nature Physics.

In their fundamental research, experimental physicists routinely bring giant yet intricate machinery to bear: Particle accelerators of enormous size smash together microscopic particles at velocities close to the speed of light, releasing unimaginable amounts of energy. In the remains of these collisions, scientists search for signatures of the fundamental forces of the universe.

Since the 1970s, a veritable zoo of particles was discovered and organized into the standard model of particle physics. Among them are quarks, the elementary building blocks of protons and neutrons. These unusual particles obey their own, quite idiosyncratic, properties that set them apart from any other form of matter. For instance, while there is only one kind of electric charge, that can be positive or negative, the behavior of quarks underlies completely different physical laws.

Prof. Stefan Scheel, head of the research group quantum optics of macroscopic systems at the University of Rostock explains, "Next to their electric charge, quarks come along with their own color charge: red, green, or blue. This, of course, has nothing to do with the colors found in a rainbow."

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New chip-scale laser isolator opens new research avenues in photonics
https://phys.org/news/2022-12-chip-scal ... onics.html
by Andrew Myers, Stanford University

Lasers are transformational devices, but one technical challenge prevents them from being even more so. The light they emit can reflect back into the laser itself and destabilize or even disable it. At real-world scales, this challenge is solved by bulky devices that use magnetism to block the harmful reflections. At chip scale, however, where engineers hope lasers will one day transform computer circuitry, effective isolators have proved elusive.

Against that backdrop, researchers at Stanford University say they have created a simple and effective chip-scale isolator that can be laid down in a layer of semiconductor-based material hundreds of times thinner than a sheet of paper.

"Chip-scale isolation is one of the great open challenges in photonics," said Jelena Vučković, a professor of electrical engineering at Stanford and senior author of the study appearing Dec. 1 in the journal Nature Photonics.

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Plasma instability may be a solution for magnetic nozzle plasma thrusters
https://phys.org/news/2022-12-plasma-in ... ozzle.html
by Tohoku University

A research group has demonstrated that spontaneously excited plasma waves may be the solution to a long-associated problem with magnetic nozzle plasma thrusters, turning conventional thinking on its head.

Details of their research were published in the journal Scientific Reports on December 5, 2022.

In magnetic nozzle radio frequency thrusters, sometimes referred to as helicon thrusters, magnetic nozzles channel and accelerate plasma to allow spacecraft to generate thrust. The technology, which harnesses electric propulsion, shows great potential for ushering in a new era of space travel. Yet the so-called "plasma detachment" problem has hampered further development.

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Researchers adapt a Nobel Prize-winning method to design new, ultra-powerful X-ray systems
https://phys.org/news/2022-12-nobel-pri ... x-ray.html
by Kimberly Hickok, SLAC National Accelerator LaboratoryAccelerator Laboratory

If scientists want to push the boundaries of, say, an X-ray laser, they may need to create some new technology. But occasionally there's no need to reinvent the wheel. Instead, scientists simply come up with a new way to use it.

Now, researchers at the Department of Energy's SLAC National Accelerator Laboratory have done just that in an effort to push the capabilities of the lab's Linac Coherent Light Source (LCLS) X-ray free-electron laser (XFEL). By adapting a technique for modern, superpowerful optical laser pulses called chirped pulse amplification (CPA), the SLAC team has designed a system capable of producing X-ray pulses ten times more powerful than before—all while staying within the LCLS's existing free-electron laser infrastructure.

The team published their results in Physical Review Letters on November 18.

"Current X-ray laser pulses from free-electron lasers have a peak power of roughly 100 gigawatts, and usually with a complex and stochastic structure," said Haoyuan Li, a postdoctoral scholar at SLAC and Stanford University and lead author of the new study.

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Large Hadron Collider Beauty releases first set of data to the public
https://phys.org/news/2022-12-large-had ... eauty.html
by CERN

The Large Hadron Collider Beauty (LHCb) experiment at CERN is the world's leading experiment in quark flavor physics with a broad particle physics program. Its data from Runs 1 and 2 of the Large Hadron Collider (LHC) has so far been used for over 600 scientific publications, including a number of significant discoveries.

While all scientific results from the LHCb collaboration are already publicly available through open access papers, the data used by the researchers to produce these results is now accessible to anyone in the world through the CERN open data portal. The data release is made in the context of CERN's Open Science Policy, reflecting the values of transparency and international collaboration enshrined in the CERN Convention for more than 60 years.

"The data collected at LHCb is a unique legacy to humanity, especially since no other experiment covers the region LHCb looks at," says Sebastian Neubert, leader of the LHCb open data project. "It has been obtained through a huge international collaborative effort, which was funded by the public. Therefore the data belongs to society."

The data sample made available amounts to 20% of the total data set collected by the LHCb experiment in 2011 and 2012 during LHC Run 1. It comprises 200 terabytes containing information obtained from proton–proton collision events filtered and recorded with the detector.

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Imposter physical particles revealed: A key advance for quantum technology
https://phys.org/news/2022-12-imposter- ... d-key.html
by Spanish National Research Council (CSIC)

The most common particles are electrons and photons, which are understood to be examples from the great families of fermions and bosons, to which all other particles in nature belong. But there is another possible category of particles, the so-called anyons. Anyons are predicted to arise inside materials small enough to confine the electronic state wave function, as they emerge from the collective dance of many interacting electrons.

One of these is named Majorana zero mode, anyonic cousins to the Majorana fermions proposed by Ettore Majorana in 1937. Majoranas, as these hypothetical anyons are affectionally called, are predicted to exhibit numerous exotic properties, such as simultaneously behaving like a particle and antiparticle, allowing mutual annihilation, and the capability to hide quantum information by encoding it nonlocally in space. The latter property specifically holds the promise of resilient quantum computing.

Since 2010, many research groups have raced to find Majoranas. Unlike fundamental particles, such as the electron or the photon, which naturally exist in a vacuum, Majorana anyons need to be created inside hybrid materials. One of the most promising platforms for realizing them is based on hybrid superconductor-semiconductor nanodevices. Over the past decade, these devices have been studied with excruciating detail, with the hope of unambiguously proving the existence of Majoranas. However, Majoranas are tricky entities, easily overlooked or mistaken with other quantum states.

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Coherent manipulation of spin qubits at room temperature
https://phys.org/news/2022-12-coherent- ... ature.html
by Chinese Academy of Sciences

A research group led by Prof. Wu Kaifeng from the Dalian Institute of Chemical Physics (DICP), Chinese Academy of Sciences recently reported the successful initialization, coherent quantum-state control, and readout of spins at room temperature using solution-grown quantum dots, which represents an important advance in quantum information science.

The study was published in Nature Nanotechnology on Dec 19th.

Quantum information science is concerned with the manipulation of the quantum version of information bits (called qubits). When people talk about materials for quantum information processing, they usually think of those manufactured using the most cutting-edge technologies and operating at very cold temperatures (below a few Kelvin), not the "warm and messy" materials synthesized in solution by chemists.

Recent years have witnessed the discovery of isolated defects in solid-state materials (such as NV centers) that have made possible room-temperature spin-qubit manipulation, but scaled-up production of these "point defects" will eventually become a challenge.