Lifeboat Foundation

Today the international LHCb collaboration at the Large Hadron Collider (LHC) presented new measurements of rare particle transformations, or decays, that provide one of the highest-precision tests yet of a key property of the Standard Model of particle physics, known as lepton flavor universality.

Previous studies of these decays had hinted at intriguing tensions with the theoretical predictions, potentially due to the effects of new particles or forces. The results of the improved and wider-reaching analysis based on the full LHC dataset collected by the experiment during Run 1 and Run 2, which were presented at a seminar at CERN held this morning, are in line with the Standard Model expectation.

A central mystery of particle physics is why the 12 elementary quarks and leptons are arranged in pairs across three generations that are identical in all but mass, with ordinary matter comprising particles from the first, lightest generation. Lepton flavor universality states that the fundamental forces are blind to the generation to which a lepton belongs.

The first measurements from a newly built gamma-ray observatory have been analyzed for signs of the decay of heavy dark matter, putting a lower limit on the hypothetical particles’ lifetime.

A pressing quest in the field of nanoelectronics is the search for a material that could replace silicon. Graphene has seemed promising for decades. But its potential has faltered along the way, due to damaging processing methods and the lack of a new electronics paradigm to embrace it. With silicon nearly maxed out in its ability to accommodate faster computing, the next big nanoelectronics platform is needed now more than ever.

Walter de Heer, Regents’ Professor in the School of Physics at the Georgia Institute of Technology, has taken a critical step forward in making the case for a successor to silicon. De Heer and his collaborators have developed a new nanoelectronics platform based on graphene —a single sheet of carbon atoms. The technology is compatible with conventional microelectronics manufacturing, a necessity for any viable alternative to silicon.

In the course of their research, published in Nature Communications, the team may have also discovered a new quasiparticle. Their discovery could lead to manufacturing smaller, faster, more efficient and more sustainable computer chips, and has potential implications for quantum and high-performance computing.

“My first impression is that the analysis is much more robust than before,” says Florencia Canelli, an experimental particle physicist at the University of Zurich in Switzerland who is a senior member of a separate LHC experiment. It has revealed how a number of surprising subtleties had conspired to produce an apparent anomaly, she says.

Renato Quagliani, an LHCb physicist at the Swiss Federal Polytechnic Institute (EPFL) in Lausanne, reported the results at CERN on 20 December, in a seminar that also attracted more than 700 viewers online. The LHCb collaboration also posted two preprints on the arXiv repository^1,2.

LHCb first reported a tenuous discrepancy in the production of muons and electrons in 2014. When collisions of protons produced massive particles called B mesons, these quickly decayed. The most frequent decay pattern produced another type of meson, called a kaon, plus pairs of particles and their antiparticles — either an electron and a positron or a muon and an antimuon. The standard model predicted that the two types of pairs should occur with roughly the same frequency, but LHCb data suggested that the electron-positron pairs occurred more often.

For decades, physicists have been hunting for a quantum-gravity model that would unify quantum physics, the laws that govern the very small, and gravity. One major obstacle has been the difficulty in testing the predictions of candidate models experimentally. But some of the models predict an effect that can be probed in the lab: a very small violation of a fundamental quantum tenet called the Pauli exclusion principle, which determines, for instance, how electrons are arranged in atoms.

A project carried out at the INFN underground laboratories under the Gran Sasso mountains in Italy, has been searching for signs of radiation produced by such a violation in the form of atomic transitions forbidden by the Pauli exclusion principle.

In two papers appearing in the journals Physical Review Letters (published on September 19, 2022) and Physical Review D (accepted for publication on December 7, 2022) the team reports that no evidence of violation has been found, thus far, ruling out some quantum-gravity models.

A single particle has no temperature. It has a certain energy or a certain speed—but it is not possible to translate that into a temperature. Only when dealing with random velocity distributions of many particles does a well-defined temperature emerge.

How can the laws of thermodynamics arise from the laws of quantum physics? This is a topic that has attracted growing attention in recent years. At TU Wien (Vienna), this question has now been pursued with computer simulations, which showed that chaos plays a crucial role: Only where chaos prevails do the well-known rules of thermodynamics follow from quantum physics.

A new kind of neutrino that’s abundant in life on Earth could explain a major anomaly in particle physics—and help us find dark matter.

Quantum entanglement is a process through which two particles become entangled and remain connected over time, even when separated by large distances. Detecting this phenomenon is of crucial importance for both the development of quantum technology and the study of quantum many-body physics.

Researchers at Tsinghua have recently carried out a study exploring the possible reasons why the reliable and efficient detection of entanglement in complex and “noisy” systems has often proved to be very challenging. Their findings, published in Physical Review Letters, hint at the existence of a trade-off between the effectiveness and efficiency of entanglement detection methods.

“Over 20 years ago, researchers discovered that most quantum states are entangled,” Xiongfeng Ma, one of the researchers who carried out the study, told Phys.org.

The cloud condensation nuclei activation of sea spray aerosol (SSA) is tightly linked to the hygroscopic properties of these particles and is defined by their physical and chemical properties. While hygroscopic sea salt in SSA strongly influences particle water uptake, the marine-derived components that make up the organic fraction of SSA constitute a complex mixture, and their effect on hygroscopic growth is unknown. To constrain the effect of organic compounds and specifically surface-active compounds that adsorb on particle interfaces, particle hygroscopic growth studies were performed on laboratory-generated model sea salt/sugar particles. For sea salt/glucose particles, ionic surfactants facilitated water uptake at low relative humidity (RH), increasing the particle growth factor (GF) by up to 7.61%, and caused a reduction in the deliquescence relative humidity (DRH), while nonionic surfactants had a minimal effect. Replacing glucose with polysaccharide laminarin in sea salt/sugar/surfactant particles caused a reduction in GF at low RHs and minimized the effect of ionic surfactants on the DRH. At RHs above the DRH, the addition of anionic or nonionic surfactants caused a decrease in GF for both sea salt/glucose and sea salt/laminarin particles. The addition of cationic surfactants, however, did not have a dampening effect on water uptake of sea salt/sugar particles and even showed a GF increase of up to 3.7% at 90% RH. An increase in the complexity of the sugar dampens the water uptake for particles containing nonionic surfactants but increases the water uptake for cationic surfactants. The cloud activation potential for 100 nm particles analyzed in this study is higher for ionic surfactants and decreases with an increase in surfactant molecular size when particle interfacial tension is considered. The surfactant effect on the hygroscopic growth and cloud activation potential of the particles containing sea salt/sugar is dependent on the surfactant ionicity and molecular size, the particle size and interfacial tension, and the interactions between inorganic salt and organic species under different RH conditions.