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Researchers have developed a new method that uses attosecond core-level spectroscopy to capture molecular dynamics in real time.

The mechanisms behind chemical reactions are complex, involving many dynamic processes that affect both the electrons and the nuclei of the involved atoms. Frequently, the strongly coupled electron and nuclear dynamics trigger radiation-less relaxation processes known as conical intersections. These dynamics underpin many significant biological and chemical functions but are notoriously difficult to detect experimentally.

The challenge in studying these dynamics stems from the difficulty of tracing the nuclear and electronic motion simultaneously. Their dynamics are intertwined and occur on ultrafast timescales, which has made capturing the molecular dynamical evolution in real time a major challenge for both physicists and chemists in recent years.

A detailed study of a reaction between a molecular ion and a neutral atom has implications for both atmospheric and interstellar chemistry.

Reactions between ions and neutral atoms or molecules occur in various settings, from planetary atmospheres to plasmas. They are also the driving force behind rich reaction chains at play in the interstellar medium (ISM)—the giant clouds of gas and dust occupying the space between stars. The ISM is cold, highly dilute, and abundant with ionizing radiation [1]. These conditions are usually unfavorable for chemistry. Yet, more than 300 molecular species have been detected in the ISM to date, of which about 80% contain carbon [2]. Now Florian Grussie at the Max Planck Institute for Nuclear Physics (MPIK) in Germany and collaborators report an experimental and theoretical study of an ion–neutral reaction: that between a neutral carbon atom and a molecular ion (HD⁺), made of a hydrogen and a deuterium (heavy hydrogen) atom [3, 4]. The study’s findings could improve our understanding of the chemistry of the ISM.

Ion–neutral reactions are fundamentally different from those involving only neutral species. Unlike typical neutral–neutral reactions, ion–neutral reactions often do not need to overcome an activation energy barrier and proceed efficiently even if the temperature approaches absolute zero. The reason for this difference is that, in ion–neutral reactions, the ion strongly polarizes the neutral atom or molecule, causing attractive long-range interactions that bring the reactants together.

While carbon nanotubes are the materials that have received most of the attention so far, they have proved very difficult to manufacture and control, so scientists are eager to find other compounds that could be used to create nanowires and nanotubes with equally interesting properties, but easier to handle.

So, Chiara Cignarella, Davide Campi and Nicola Marzari thought to use computer simulations to parse known three-dimensional crystals, looking for those that—based on their structural and electronic properties —look like they could be easily “exfoliated,” essentially peeling away from them a stable 1-D structure. The same method has been successfully used in the past to study 2D materials, but this is the first application to their 1-D counterparts.

The researchers started from a collection of over 780,000 crystals, taken from various databases found in the literature and held together by van der Waals forces, the sort of weak interactions that happen when atoms are close enough for their electrons to overlap. Then they applied an algorithm that considered the spatial organization of their atoms looking for the ones that incorporated wire-like structures, and calculated how much energy would be necessary to separate that 1-D structure from the rest of the crystal.

The Higgs boson has an extremely short lifespan, living for about 10–22 seconds before quickly decaying into other particles. For comparison, in that brief time, light can only travel about the width of a small atomic nucleus. Scientists study the Higgs boson by detecting its decay products in particle collisions at the Large Hadron Collider. But what if the Higgs boson could also decay into unexpected new particles that are long-lived? What if these particles can travel a few centimeters through the detector before they decay? These long-lived particles (LLPs) could shed light on some of the universe’s biggest mysteries, such as the reason matter prevailed over antimatter in the early universe and the nature of dark matter. Searching for LLPs is extremely challenging because they rarely interact with matter, making them difficult to observe in a particle detector. However, their unusual signatures provide exciting prospects for discovery. Unlike particles that leave a continuous track, LLPs result in noticeable displacements between their production and decay points within the detector. Identifying such a signature requires dedicated algorithms. In a new study submitted to Physical Review Letters, ATLAS scientists used a new algorithm to search for LLPs produced in the decay of Higgs bosons. Boosting sensitivity with a new algorithm Figure 1: A comparison of the radial distributions of reconstructed displaced vertices in a simulated long-lived particle (LLP) sample using the legacy and new (updated) track reconstruction configurations. The circular markers represent reconstructed vertices that are matched to LLP decay vertices and the dashed lines represent reconstructed vertices from background decay vertices (non-LLP). (Image: ATLAS Collaboration/CERN) Despite being critical to the LLP searches, dedicated reconstruction algorithms were previously so resource intensive that they could only be applied to less than 10% of all recorded ATLAS data. Recently, however, ATLAS scientists implemented a new “Large-Radius Tracking” algorithm (LRT), which significantly speeds up the reconstruction of charged particle trajectories in the ATLAS Inner Detector that do not point back to the primary proton-proton collision point, while drastically reducing backgrounds and random combinations of detector signals. The LRT algorithm is executed after the primary tracking iteration using exclusively the detector hits (energy deposits from charged particles recorded in individual detector elements) not already assigned to primary tracks. As a result, ATLAS saw an enormous increase in the efficiency of identifying LLP decays (see Figure 1). The new algorithm also improved CPU processing time more than tenfold compared to the legacy implementation, and the disk space usage per event was reduced by more than a factor of 50. These improvements enabled physicists to fully integrate the LRT algorithm into the standard ATLAS event reconstruction chain. Now, every recorded collision event can be scrutinized for the presence of new LLPs, greatly enhancing the discovery potential of such signatures. Physicists are searching for Higgs bosons decaying into new long-lived particles, which may leave a ‘displaced’ signature in the ATLAS detector. Exploring the dark with the Higgs boson Figure 2: Observed 95% confidence-limit on the decay of the Higgs boson to a pair of long-lived s particles that decay back to Standard-Model particles shown as a function of the mean proper decay length ( of the long-lived particle. The observed limits for the Higgs Portal model from the previous ATLAS search are shown with the dotted lines. (Image: ATLAS Collaboration/CERN) In their new result, ATLAS scientists employed the LRT algorithm to search for LLPs that decay hadronically, leaving a distinct signature of one or more hadronic “jets” of particles originating at a significantly displaced position from the proton–proton collision point (a displaced vertex). Physicists also focused on the Higgs “portal” model, in which the Higgs boson mediates interactions with dark-matter particles through its coupling to a neutral boson s, resulting in exotic decays of the Higgs boson to a pair of long-lived s particles that decay into Standard-Model particles. The ATLAS team studied collision events with unique characteristics consistent with the production of the Higgs boson. The background processes that mimic the LLP signature are complex and challenging to model. To achieve good discrimination between signal and background processes, ATLAS physicists used a machine learning algorithm trained to isolate events with jets arising from LLP decays. Complementary to this, a dedicated displaced vertex reconstruction algorithm was used to pinpoint the origin of hadronic jets originating from the decay of LLPs. This new search did not uncover any events featuring Higgs-boson decays to LLPs. It improves bounds on Higgs-boson decays to LLPs by a factor of 10 to 40 times compared to the previous search using the exact same dataset (see Figure 2)! For the first time at the LHC, bounds on exotic decays of the Higgs boson for low LLP masses (less than 16 GeV) have surpassed results for direct searches of exotic Higgs-boson decays to undetected states. About the event display: A 13 TeV collision event recorded by the ATLAS experiment containing two displaced decay vertices (blue circles) significantly displaced from the beam line showing “prompt” non displaced decay vertices (pink circles). The event characteristics are compatible with what would be expected if a Higgs boson is produced in association with a Z boson (decaying to two electrons indicated by green towers), and decayed into two LLPs (decaying into two b-quarks each). Tracks shown in yellow and jets are indicated by cones. The green and yellow blocks correspond to energy deposition in the electromagnetic and hadronic calorimeters, respectively. (Image: ATLAS Collaboration/CERN) Learn more Search for light long-lived particles in proton-proton collisions at 13 TeV using displaced vertices in the ATLAS inner detector (Submitted to PRL, arXiv:2403.15332, see figures) Performance of the reconstruction of large impact parameter tracks in the inner detector of ATLAS (Eur. Phys. J. C 83 (2023) 1,081, arXiv:2304.12867, see figures) Search for exotic decays of the Higgs boson into long-lived particles in proton-proton collisions at 13 TeV using displaced vertices in the ATLAS inner detector (JHEP 11 (2021) 229, arXiv:2107.06092, see figures)

Similar to how a radio antenna plucks a broadcast from the air and concentrates the energy into a song, individual atoms can collect and concentrate the energy of light into a strong, localized signal that researchers can use to study the fundamental building blocks of matter.

A crested bigscaleCredit: Karen Osborn/Smithsonian

“But what isn’t absorbed side-scatters into the layer, and it’s absorbed by the neighboring pigments that are all packed right up close to it,” Osborn told Wired. “And so what they’ve done is create this super-efficient, very-little-material system where they can basically build a light trap with just the pigment particles and nothing else.”

The result? Strange and terrifying deep-sea species, like the crested bigscale, fangtooth, and Pacific blackdragon, all of which appear in the deep sea as barely more than faint silhouettes.

Recent advancements in spintronics have enabled better prediction and control of spin currents by studying the magnetic properties and temperature effects on materials.

Spintronics is attracting significant interest as a promising alternative to conventional electronics, offering potential benefits such as lower power consumption, faster operation, non-volatility, and the possibility of introducing new functionalities.

Spintronics exploits the intrinsic spin of electrons, and fundamental to the field is controlling the flows of the spin degree of freedom, i.e., spin currents. Scientists are constantly looking at ways to create, remove, and control them for future applications.

Research groups from the University of Tsukuba and the University of Rennes have discovered a novel phenomenon in which a nested structure of carbon nanotubes enveloped in boron nitride nanotubes facilitates a unique electron escape route when exposed to light. This finding introduces promising avenues for various applications, including the creation of high-speed optical devices, rapid control of electrons and other particles and efficient heat dissipation from devices.

Collections of mobile, interacting objects—flocks of birds, colonies of bacterial, or teams of robots—can sometimes behave like solid materials, executing organized rotations or gliding coherently in one direction. But why such systems display one kind of collective organization rather than another has remained unclear. Now researchers have developed a theory that can predict the pattern most likely to emerge under specific conditions [1]. The theory, they hope, may be of use in designing living and artificial materials that can autonomously adapt to their environment.

An “active material” is any system made up of interacting objects able to move under their own power, such as animals, cells, or robots. In so-called active solids, a subset of active materials, strong cohesion between neighboring elements makes the collective act somewhat like a solid. Examples include clusters of certain cell types and networks of robots with rigid connections.

Active solids can display several kinds of collective, organized motion, says Claudio Hernández-López, a PhD student at the École Normale Supérieure and Sorbonne University in France. For example, researchers have observed both coherent rotations and coherent translations in collections of microbes from the phylum Placozoa. Existing theories, however, fail to explain pattern selection—why, if several patterns are possible, does one pattern of behavior emerge rather than another?