international collaboration in physics research – Science

New Particles Found at High Energies

Katie Riggs — Thu, 11 Dec 2025 07:08:36 +0000

In the relentless pursuit of understanding the fundamental building blocks of our universe, physicists at the forefront of particle physics are constantly devising ingenious experiments to probe the very fabric of reality. Today, a groundbreaking new investigation emerges from the esteemed European Physical Journal C, promising to illuminate the enigmatic realm of sub-GeV scalar particles. This ambitious endeavor, spearheaded by a collaborative team of international researchers, ventures into the high-energy dance of electron-positron collisions, seeking to uncover evidence of these elusive entities that have, until now, largely evaded direct detection. The hunt is on for particles with masses below one billion electron-volts (GeV), a threshold that places them in a fascinating and largely unexplored territory within the Standard Model of particle physics, hinting at potentially new physics beyond our current understanding.

The Standard Model, while remarkably successful in describing the known fundamental particles and forces, is not without its limitations. It leaves certain fundamental questions unanswered, such as the nature of dark matter and dark energy, and the origin of neutrino masses. The existence of new, low-mass scalar particles could provide crucial clues to bridging these gaps and ushering in a new era of physics. These hypothetical particles, if they exist and interact with matter in specific ways, could play a pivotal role in phenomena we only observe indirectly. Their discovery would not merely be an incremental step; it would represent a significant leap forward, potentially rewriting textbooks and fundamentally altering our cosmic perspective, a prospect that has the global scientific community buzzing with anticipation and excitement.

The specific experimental setup at the heart of this investigation involves the precise collision of electrons ($e^-$) and their antimatter counterparts, positrons ($e^+$). These high-energy collisions are not merely random events; they are meticulously orchestrated to generate a flurry of other particles, including potentially the very scalars physicists are searching for. By analyzing the debris of these collisions with sophisticated detectors, researchers can reconstruct the events and look for the tell-tale signatures of undiscovered particles. The energy of these collisions is critical, tuned to specific thresholds that maximize the probability of producing particles within the sub-GeV mass range, a delicate balancing act requiring immense precision and advanced technological capabilities.

One of the primary targets of this search is the interaction of these hypothetical sub-GeV scalars with existing Standard Model particles, particularly photons ($\gamma$). If these scalars can decay into pairs of photons, their presence could be inferred from the detection of these high-energy light particles. The precise energy and angular distribution of these photon pairs would then serve as a unique fingerprint, distinguishing them from background processes that also produce photons. This sophisticated analysis relies on the exquisite sensitivity of modern particle detectors, capable of measuring the energy and trajectory of individual photons with remarkable accuracy.

Furthermore, the researchers are exploring scenarios where these scalar particles might interact with leptons, such as muons ($\mu$) and tau leptons ($\tau$). An interaction with these heavier cousins of the electron could lead to their production in electron-positron annihilation events, again with distinct signatures that can be identified by the detectors. The intricate web of possible interactions and decay channels is a testament to the complexity and depth of theoretical particle physics, and this experiment aims to empirically test these predictions, moving from abstract theoretical constructs to concrete observational evidence.

The painstaking process of data analysis is as crucial as the experimental setup itself. Billions of collision events are recorded, forming a vast dataset that requires advanced computational techniques to sift through. Physicists employ sophisticated algorithms and statistical methods to filter out known background processes and identify any statistically significant deviations that might indicate the presence of new physics. This involves meticulous calibration of detectors and a deep understanding of all known particle interactions to ensure that any observed anomaly is not simply a misinterpretation of familiar phenomena.

The challenge lies in distinguishing a faint signal from the overwhelming noise of well-understood particle interactions. The sub-GeV scalar signals are expected to be subtle, potentially appearing as slight excesses in specific energy or momentum ranges. This necessitates a rigorous statistical analysis to determine the probability that the observed signal could arise from random fluctuations in the background. A finding is considered robust only when the probability of a statistical fluctuation mimicking the signal is exceedingly small, often meeting the stringent “five-sigma” criterion in particle physics.

The research paper detailing this search, published in The European Physical Journal C, provides a comprehensive account of the experimental methodology, the theoretical motivations, and the stringent analysis techniques employed. It outlines the specific kinematic regions and decay channels that were investigated, offering a detailed map of the parameter space explored in the hunt for these elusive particles. The paper serves as a critical blueprint for future investigations and a testament to the collaborative spirit that drives modern scientific discovery.

The potential implications of discovering a sub-GeV scalar particle are far-reaching. It could offer a new perspective on the hierarchy problem, the puzzle of why the Higgs boson is so much lighter than expected based on quantum corrections. It might also shed light on the nature of dark matter, a mysterious substance that makes up a significant portion of the universe’s mass but does not interact with light. A light scalar could, in certain models, be a candidate for dark matter particles or a mediator between dark matter and the visible sector.

Moreover, the existence of such particles could provide a deeper understanding of the early universe. Their presence could have influenced the Big Bang nucleosynthesis, the process that formed the first light elements, or played a role in the cosmic phase transitions that shaped the universe in its infancy. The broader cosmological consequences of finding even a single new fundamental particle cannot be overstated, as it forces us to re-evaluate our models of cosmic evolution and structure formation.

The collaborative nature of this research is a hallmark of modern high-energy physics. Scientists from various institutions, bringing diverse expertise and perspectives, pool their resources and knowledge to tackle these monumental challenges. This interdisciplinary approach fosters innovation and accelerates the pace of discovery, as ideas are exchanged and refined in a dynamic and intellectually stimulating environment, underscoring the global effort to decipher the universe’s deepest secrets.

While this particular investigation may not have yet yielded a definitive discovery, the stringent limits set on the properties of these sub-GeV scalars are equally valuable. These null results constrain theoretical models, guiding future research and narrowing down the possibilities for new physics. The absence of a signal in certain parameter spaces represents progress, as it forces theorists to refine their predictions and explore alternative avenues, a crucial part of the scientific process that often goes unheralded but is vital for scientific advancement.

The experimental techniques employed in this search are at the cutting edge of technological innovation. The detectors used are incredibly complex instruments, designed to capture and measure the faint whispers of ephemeral particles. These detectors are the result of decades of research and development, pushing the boundaries of engineering and material science to achieve unprecedented levels of sensitivity and precision, a testament to human ingenuity in the face of cosmic mystery.

Looking ahead, this research paves the way for future experiments with even greater sensitivity and energy reach. As particle accelerators become more powerful and detectors more sophisticated, the ability to probe the sub-GeV mass range with even greater precision will increase. This ongoing quest for new physics is a marathon, not a sprint, requiring sustained investment in fundamental research and a commitment to exploring the unknown, driven by an insatiable curiosity about our place in the cosmos and the fundamental laws that govern it.

This ongoing exploration into the sub-GeV scalar realm underscores the profound beauty and intricate complexity of the universe. Each experiment, whether it yields a direct detection or sets new limits, contributes to our ever-evolving understanding of fundamental physics. The quest for these elusive particles is a testament to humanity’s enduring drive to unravel the mysteries of existence, pushing the boundaries of knowledge one collision, one measurement, one theoretical insight at a time, in a pursuit that promises to reshape our perception of reality itself.

Subject of Research: Search for sub-GeV scalar particles in electron-positron collisions.

Article Title: Search for sub-GeV scalars in $e^+e^-$ collisions.

Article References: Cogollo, D., Oviedo-Torres, Y.M., Queiroz, F.S. et al. Search for sub-GeV scalars in $e^+e^-$ collisions. Eur. Phys. J. C 85, 1404 (2025). https://doi.org/10.1140/epjc/s10052-025-15094-w

Image Credits: AI Generated

DOI: https://doi.org/10.1140/epjc/s10052-025-15094-w

Keywords**: Sub-GeV scalars, electron-positron collisions, particle physics, Standard Model, new physics, fundamental particles, scalar bosons, lepton collisions, theoretical physics, experimental physics.

Scientists Develop “Knob” to Control Topological Spin Textures in Materials

Katie Riggs — Mon, 06 Oct 2025 17:15:52 +0000

In a pioneering convergence of photonics and condensed matter physics, an international consortium of researchers has introduced a revolutionary optical technique to fabricate and govern topological solitons in ferroelectric materials, offering transformative potential for the future of memory devices and information processing technologies. This breakthrough leverages the intrinsic properties of structured light to precisely control nano-scale topological configurations such as skyrmions and the rarely observed antiskyrmions within ultrathin ferroelectric films.

Published in the prestigious journal Physical Review B, this study hinges on the novel application of the Poincaré sphere—a longstanding geometric tool traditionally employed to describe light’s polarization states—as an active mechanism for engineering topological solitons. By manipulating the phase and geometry of laser beams, the researchers achieved unprecedented dynamic control over the formation, evolution, and interaction of complex topological structures. This approach transcends conventional manipulation techniques, offering a fully optical and ultrafast avenue to harness and reconfigure matter at the nanoscale.

Central to this advancement is the concept of “Poincaré sphere engineering,” which effectively serves as a sophisticated dial to navigate and modulate the topological landscape within ferroelectric materials. The research team, spearheaded by experts from the University of Arkansas and Nanyang Technological University, demonstrated that by adjusting the position on the Poincaré sphere, it is possible to seamlessly toggle between skyrmion, antiskyrmion, and vortex states within the ferroelectric films. These transitions occur with a level of precision and fluidity that was hitherto unattainable, underscoring the vast potential of structured light in nanoscale material control.

Utilizing advanced molecular dynamics simulation techniques, the researchers simulated interactions between tailored laser beams and ferroelectric ultrathin films. Distinct laser modes, including doughnut-shaped Laguerre-Gaussian beams and two-lobed Hermite-Gaussian modes, were employed to imprint intricate spatial patterns onto the polarization textures of the material. This deliberate sculpting of the polarization landscape generated a diverse array of dynamic topological configurations, encompassing vortex arrays, skyrmion-antiskyrmion hybrids, and controllable chirality domains, all modulated within femtosecond timescales.

what distinguishes this method is its purely optical nature, avoiding complexities associated with traditional electrical or mechanical manipulations. The rapid, non-contact, and tunable switching of topological states ensures that the solitons maintain their intrinsic robustness—a hallmark of topological protection—which is indispensable for practical applications like ultra-high-density, non-volatile memory storage. The ability to finely tune the transitions between different solitonic states introduces a new dimension of control, allowing memory and logic devices to be engineered with enhanced functionality and stability.

Furthermore, the discovery opens the door to a paradigm shift in how researchers approach topological matter, positioning light itself as a versatile control knob for quantum and classical topological excitations. This optical control framework promises to facilitate experimental studies of quasiparticles and emergent phenomena in condensed matter systems, with potential ripple effects across quantum computing platforms, high-capacity optical communication networks, and beyond.

The research team envisions further explorations extending these optical topological engineering principles to other physical domains, including magnetic materials and acoustic lattices. Such cross-disciplinary efforts are expected to unravel novel classes of topological excitations and control schemes, significantly enriching the broader scientific understanding of topology in low-dimensional and strongly correlated systems.

To translate their theoretical models into laboratory realities, the scientists are pursuing experimental implementations using state-of-the-art pump-probe optical techniques that can capture the ultrafast dynamics of these solitons in real materials. These time-resolved measurements aim to validate the simulation results, offering tangible evidence of dynamic topological control via structured light and illuminating pathways toward device integration.

This groundbreaking work cements the Poincaré sphere’s transformation from a purely conceptual polarization representation into a practical and powerful tool for materials engineering. By marrying optical physics with condensed matter science, the study propels topological solitons from theoretical curiosities to actionable entities with profound technological implications.

The convergence of topology, optics, and material science embodied by this research promises to unlock new frontiers in nanoscale information processing, where bits of data are encoded not just by electron charge, but by the very fabric of the material’s polarization topology. As the field advances, these topologically engineered solitons could herald the next revolution in memory technologies, with unparalleled speed, efficiency, and stability.

In essence, this study showcases how intrinsic geometric concepts of light can orchestrate matter’s most fundamental structures, establishing an all-optical toolkit for sculpting the quantum landscape. The implications ripple far beyond ferroelectrics, suggesting a future where light-driven topological design becomes a universal platform for controlling quantum materials and devices.

As the research community continues to explore and refine these techniques, the horizon is bright for novel optoelectronic devices that exploit dynamical topological solitons for ultrafast computing and robust information storage. This pioneering approach not only enhances our grasp of topological phenomena but also paves the way for next-generation technologies at the nexus of photonics and condensed matter physics.

Subject of Research: Optical engineering and control of topological solitons in ferroelectric materials using structured light and Poincaré sphere manipulation

Article Title: Poincaré sphere engineering of dynamical ferroelectric topological solitons

Web References: DOI: 10.1103/xr8r-h3x9

Image Credits: Y. Shen et al.

Keywords

Topological solitons, skyrmions, antiskyrmions, Poincaré sphere, structured light, ferroelectric materials, molecular dynamics simulations, Laguerre-Gaussian beams, Hermite-Gaussian modes, nanoscale vortices, ultrafast optical control, condensed matter physics, photonics, topological memory devices

Revolutionizing Nuclear Physics: Introducing the New Standards

Katie Riggs — Thu, 22 May 2025 18:40:39 +0000

In a remarkable advancement that is poised to redefine the precision of nuclear measurements, an international team of physicists led by the Paul Scherrer Institute (PSI) has achieved an unprecedentedly accurate determination of the atomic nucleus radius of muonic helium-3 ions. By leveraging cutting-edge laser spectroscopy techniques in an environment enriched by PSI’s unique proton accelerator facility, the researchers have refined measurements that probe the fundamental structure of matter with blistering precision. This breakthrough not only bolsters the consistency of theoretical nuclear models but also sets a new benchmark for atomic physics experiments worldwide.

Fundamentally, helium-3, a rare isotope of helium, exhibits intriguing features due to its nuclear composition consisting of two protons and just one neutron. Unlike the more abundant helium-4 isotope, which contains two neutrons, helium-3’s comparatively “slimmed-down” nucleus presents physicists with a cleaner and more tractable system for testing the fabric of nuclear forces. The challenge in directly measuring such a nucleus with extreme precision lies in the scale at which nuclear phenomena operate–on the order of femtometres, or quadrillionths of a meter. The current study pinpoints the radius of helium-3’s nucleus at approximately 1.97007 femtometres, a measurement made possible only by innovative experimental strategies.

Central to this precision is the use of muonic helium-3 atoms, which unlike conventional atoms, replace the two orbiting electrons with muons. Muons are elementary particles akin to electrons but about 200 times more massive. This increased mass drastically shrinks the muon’s orbital radius around the nucleus, resulting in a much stronger overlap between the muon’s wave function and the nuclear charge distribution. This enhanced interaction amplifies the sensitivity of spectroscopic measurements to the spatial extent of the nucleus, essentially turning the muon into an exceptionally effective “probe” of nuclear structure.

The formation and study of muonic helium-3 ions require exceptionally specialized infrastructure. At PSI, a proton accelerator generates intense beams of low-energy negative muons, approximately 500 muons per second at energies near one kiloelectron-volt. These slow muons can be captured by helium-3 atoms to form muonic helium-3 ions suitable for precision spectroscopy. PSI’s in-house beamline technology is currently the only facility in the world capable of producing such low-energy, abundant muon beams ideal for this experiment, underscoring the institute’s worldwide scientific prominence.

Laser spectroscopy is the cornerstone technique for determining the nuclear charge radius in this experiment. The team developed a highly specialized, custom-built laser system capable of emitting pulses of light synchronized to the fleeting presence of a muon entering the experimental setup. A thin foil detector first identifies the passage of a muon, triggering an immediate laser pulse. When the laser light frequency resonates perfectly with a specific atomic transition in muonic helium-3, it excites the muon to a higher energy level. This excited state quickly decays within picoseconds, emitting X-ray photons whose characteristics inform the exact nuclear charge radius indirectly but with exquisite precision.

The physical principle underlying these measurements involves comparing the energy levels of the muonic atom to the theoretically predicted values, which depend sensitively on the size of the nuclear charge distribution. By fine-tuning the laser frequency until resonance is achieved, the experimenters can deduce the exact dimensions of the nucleus with unparalleled accuracy. This method has matured substantially in recent years, supported by the successful measurement of muonic hydrogen and helium-4, which preceded this helium-3 investigation.

The results of this latest study dovetail conspicuously well with existing data acquired through alternative measurement techniques, which historically faced larger uncertainties. Intriguingly, the helium-3 measurement from PSI exhibits approximately fifteen times greater precision than earlier experiments, significantly tightening the constraints on nuclear theory. This precision enables theorists employing ab initio nuclear models—calculations rooted directly in the fundamental interactions between protons and neutrons without adjustable parameters—to benchmark and refine their predictions with an unprecedented level of confidence.

Moreover, these precise charge radii carry profound implications beyond nuclear structure alone. Helium ions with more or fewer electrons serve as critical testbeds for validating quantum electrodynamics (QED), the quantum field theory describing electromagnetic interactions. By comparing muonic atom results against data from conventional helium ions and neutral helium atoms—both elegantly complex “few-body” systems—physicists can scrutinize QED predictions under extreme conditions. Discrepancies might hint at new physics, possibly transcending the current Standard Model of particle physics, thereby advancing fundamental science.

A particularly captivating historical backdrop is the earlier measurement of muonic hydrogen conducted by PSI’s team, which initially stunned the community by revealing a proton radius smaller than values obtained by traditional electron-based methods. This “proton radius puzzle” triggered intense debate regarding measurement validity and underlying theory. However, numerous independent confirmations since then have affirmed the accuracy of that result, establishing robust trust in muonic atom spectroscopy as a precise tool for nuclear characterization.

The successful helium-3 measurement was enabled not only by PSI’s unique technical capabilities but also by sophisticated instrumentation innovations developed by the research team. The real-time detection and immediate triggering of the laser pulse required the integration of ultra-thin detectors and state-of-the-art timing electronics. Such technical prowess surmounted the challenge of muons’ extremely short lifetimes and fleeting atomic states, highlighting the convergence of experimental physics ingenuity and advanced engineering.

Looking ahead, Aldo Antognini and collaborators envision expanding these techniques to investigate hyperfine structure in muonic atoms. Hyperfine splitting involves subtle energy separations that arise from interactions between nuclear spin and magnetic moments, unlocking a new dimension of insight into nuclear properties and the interplay of fundamental forces. Experiments probing muonic hydrogen hyperfine transitions are underway, with plans to extend similar studies to muonic helium. Realizing these ambitions demands significant enhancements in laser power and precision, with ongoing developments at PSI and ETH Zurich aiming to meet these stringent requirements.

The wider international scientific community has recognized the impact of this milestone, with complementary follow-up experiments currently progressing at institutions across Amsterdam, Garching, China, and Switzerland. These collaborative efforts underscore the global importance of ultrahigh-precision nuclear measurements to challenges in atomic and nuclear physics that resonate well beyond their apparent scale. As these precision probes evolve, they may ultimately contribute crucial clues in the continuing quest to uncover physics beyond prevailing paradigms.

In sum, this landmark achievement in measuring the nuclear radius of muonic helium-3 epitomizes the fusion of innovative experimental design, sophisticated theoretical frameworks, and relentless international collaboration. By peeling back the veil on atomic nuclei with extraordinary clarity, the study fuels progress toward a deeper understanding of the universe’s fundamental building blocks and inspires new frontiers for quantum science and technology.

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Subject of Research: Not applicable
Article Title: The helion charge radius from laser spectroscopy of muonic helium-3 ions
News Publication Date: 22-May-2025
Image Credits: © Scanderbeg Sauer Photography

Keywords

Muonic helium-3, nuclear charge radius, laser spectroscopy, Paul Scherrer Institute, proton accelerator, muons, atomic nucleus, quantum electrodynamics, ab initio nuclear theory, hyperfine splitting, fundamental physics, precision measurement

3D Material Retains 2D Quantum Traits in Magnetic Semiconductor Breakthrough

Katie Riggs — Wed, 19 Feb 2025 11:04:52 +0000

In the evolving realm of quantum technology, a significant breakthrough has emerged from an international collaboration led by physicists at Penn State and Columbia University. The inherent challenge of harnessing the unique properties of quantum mechanics, particularly the behavior of subatomic particles, amidst the complexities of three-dimensional (3D) materials has been a long-standing issue in the field. This innovative research, published in the esteemed journal Nature Materials, sheds light on the ability to maintain quantum characteristics in layered materials, paving the way for advancements in fields ranging from optical systems to advanced computing.

Historically, the properties that make quantum materials so remarkable often dissipate when scaled to macroscopic dimensions. As quantum behavior is typically observed in two-dimensional (2D) systems, the quest to extend these functionalities into 3D materials has proven difficult. Created from a thin layer of atoms, 2D materials, such as graphene, provide a unique playground for quantum phenomena. Yet the challenge has always been their stable integration into practical applications that necessitate bulk materials.

At the core of this research lies the examination of excitons, quasiparticles with fascinating optical properties that are essential to the transport of energy without electrical charge. These excitons are generally produced in semiconductors when light interacts with the material, energizing electrons and generating excitons comprised of an excited electron and the associated hole it leaves behind. While excitons reveal optimal performance in 2D configurations, their stability tends to diminish within bulk materials like silicon, where the binding energy is relatively weak.

The conventional methods employed to achieve 2D materials often involve labor-intensive processes such as mechanical exfoliation. This technique, notable for its role in isolating graphene, requires meticulous handling; however, this technique doesn’t lend itself well to the mass production of stable excitons in larger, practical formats. Recognizing this limitation, the research team sought an alternative by leveraging the principles of magnetism, targeting chromium sulfide bromide (CrSBr), a unique layered magnetic semiconductor.

CrSBr operates as a normal semiconductor at room temperature, reminiscent of silicon, but exhibits remarkable changes under cooled conditions. By lowering its temperature to approximately -223 degrees Fahrenheit, this material transitions to an antiferromagnetic state. This transformation enables a distinctive arrangement wherein the magnetic moments or spins of its constituent particles align in a consistent and alternating pattern across the layers. The innovative aspect of this research is that the antiferromagnetic ordering in CrSBr forms a boundary that effectively confines excitons to layers with identical spin directions, thus preventing them from traversing neighboring layers that possess opposite spins.

Through advanced optical spectroscopy techniques coupled with theoretical modeling, the researchers demonstrated that the confinement of excitons remains robust regardless of the number of layers present in the semiconductor system. This intriguing approach empowers the researchers to achieve the desired quantum confinement effects akin to those seen in traditional 2D materials, but within the vastly greater context of bulk materials.

Further validation of these findings came from a collaborative effort with researchers from Germany. Florian Dirnberger and Alexey Chernikov at TUD Dresden University of Technology independently studied the same magnetic semiconductors. Upon comparison of results, both research groups found remarkable agreement, lending credence to their findings and suggesting a deeper, perhaps universal, understanding of exciton behavior in magnetic semiconductors.

The implications of this breakthrough cannot be overstated. As we stand on the brink of a technology-driven era, the ability to confine and control excitons in bulk materials opens doors to new methodologies in advanced optical systems and quantum technologies. Applications could include next-generation lasers, energy-efficient optics, and revolutionary quantum computing methods that maximize efficiency through enhanced exciton stability.

In essence, the marriage of magnetism, quantum dynamics, and advanced semiconductor physics embodies the essence of this pioneering work. By revealing the underlying interactions and behaviors of excitons within a layered magnetic framework, researchers have not only advanced the field but potentially charted a course towards unprecedented developments in technology.

As momentum builds around this groundbreaking study, it’s noteworthy to highlight that the research received substantial backing from esteemed organizations, including the U.S. Department of Energy and the National Science Foundation. With such strong institutional support, the future of quantum technology looks exceptionally promising.

The journey to unravel the complexities of quantum behaviors continues, with multi-disciplinary approaches being crucial for future explorations. The collaboration across institutions and countries stands as a testament to the collective effort that is essential in navigating the intricacies of advanced materials and their behaviors. As researchers push the envelope of what is known, the fusion of ideas and innovations in this realm will undoubtedly shape the next wave of technological advancements.

This collaboration between notable universities not only demonstrates the importance of global scientific dialogue but also sets a precedent for future research endeavors. By effectively capturing and controlling the dynamics of excitons, the implications extend far beyond fundamental physics; they resonate through a variety of fields poised for disruption.

The integration of insights from disparate fields exemplifies how interconnected the fabric of scientific inquiry has become. As researchers delve deeper into the intersection of magnetism and excitonic behavior, they will inevitably yield findings that could transform our understanding of materials at both fundamental and applied levels. With each significant discovery, we inch closer to realizing the full potential of quantum technologies.

As we look towards the future, the synergy of innovative research, inter-institutional collaboration, and the unyielding pursuit of knowledge will be the driving forces behind the next generation of scientific breakthroughs.

Subject of Research:
Article Title: Magnetically confined surface and bulk excitons in a layered antiferromagnet
News Publication Date: 19-Feb-2025
Web References: Nature Materials
References:
Image Credits: Yinming Shao and team/Penn State

Keywords