Baryon number is one of the fundamental quantum properties used to distinguish ordinary matter from antimatter. Protons and neutrons each carry a baryon number of one, while their antimatter counterparts carry minus one. In everyday conditions, baryon number appears to be conserved: when particles collide or decay, the total amount of baryon number remains unchanged. Yet conservation does not explain where that number resides inside a proton. For much of modern particle physics, the simplest answer was that it belongs to the proton’s three valence quarks—two up quarks and one down quark. The new findings suggest that this familiar description may be incomplete.

The proton is not a static trio of pointlike particles. According to quantum chromodynamics, or QCD, the theory of the strong force, quarks are bound together by gluons, the force-carrying particles of the strong interaction. Gluons themselves interact with one another, creating a constantly fluctuating field filled with virtual quark-antiquark pairs and gluonic excitations. At high energies, the proton behaves less like a compact object with three clearly separated ingredients and more like a dynamic quantum system. Its mass, spin, internal momentum and other properties emerge from the combined behavior of quarks and gluons. The origin of baryon number has remained one of the most difficult pieces of this internal puzzle.

The alternative explanation tested at RHIC is known as the baryon junction model. In this picture, the three color fields associated with the proton’s quarks meet at a common gluonic connection, forming a Y-shaped topology. The junction carries the proton’s baryon number, while the quarks can move away from it or be rearranged during a violent collision. This is fundamentally different from treating baryon number as a label permanently attached to the three valence quarks. If the junction picture is correct, baryon number can travel through the gluon field even when the original quarks are displaced, absorbed into a larger system or separated from the structure that initially contained them.

Testing the two possibilities requires more than simply counting protons after a collision. Electric charge and baryon number are related but not identical. Quarks carry both electric charge and baryon number, whereas gluons carry color charge but no electric charge or baryon number in the conventional particle accounting. By comparing how electric charge and baryon number move through the debris of high-energy collisions, physicists can search for evidence that the two quantities are transported by different mechanisms. The STAR Collaboration used several complementary collision environments at RHIC, including interactions between photons and gold nuclei as well as central and peripheral collisions between heavy nuclei.

RHIC accelerates atomic nuclei to speeds approaching that of light and brings them into collision, briefly creating matter under extreme temperatures and densities. In head-on gold-gold collisions, the energy density can become high enough to produce a quark-gluon plasma, a state in which quarks and gluons are no longer confined inside individual protons and neutrons. Glancing collisions create different geometries and particle densities, while photon-induced interactions provide a cleaner way to probe the internal structure of a nucleus and its constituents. Across these conditions, the STAR researchers tracked the distribution of particles carrying baryon number and compared it with the movement of electric charge.

The results consistently showed that baryon number was transported farther and behaved differently from what would be expected if it were tied exclusively to the proton’s valence quarks. In particular, baryon number appeared to move more readily than electric charge under the collision conditions studied. This separation is difficult to explain using a simple three-quark picture, because the valence quarks carry both properties together. The observations instead align with a mechanism in which the gluonic junction can transport baryon number independently of the detailed paths followed by the quarks. The measurements do not mean that quarks are irrelevant, but they indicate that the gluon field plays a direct and essential role in preserving the proton’s identity during violent rearrangements.

The finding is especially important because it connects an abstract feature of QCD with measurable behavior in nuclear collisions. Baryon junctions have appeared in theoretical calculations and models of high-energy particle production for decades, but their role has been difficult to isolate experimentally. The STAR measurements provide a consistent pattern across different collision systems, strengthening the case that the junction is more than a mathematical convenience. By studying how baryon number is shifted away from its original rapidity region—the particle-physics measure of motion along the beam direction—researchers can determine how efficiently it is transported through the strongly interacting medium. The observed transport favors junction-based dynamics over a model in which only the original valence quarks carry the proton’s baryon number.

The implications reach beyond the structure of a single proton. Understanding how baryon number is stored and transported may improve models of the quark-gluon plasma, the dense matter created in neutron-star interiors and the earliest moments of the Universe. It may also clarify how the strong interaction helps produce the remarkable stability of ordinary matter. The matter-antimatter imbalance presents an even larger mystery: the known Universe contains vastly more matter than antimatter, although many fundamental processes appear to treat the two similarly. The baryon junction results do not solve that imbalance, but they offer a more precise view of how baryonic matter is organized and how its defining quantum number survives when matter is heated, compressed and broken apart.

The researchers emphasize that the evidence favors the baryon junction model rather than establishing that all baryon number is carried exclusively by gluons. Future experiments will be needed to determine how the junction shares responsibility with quarks and how its behavior changes when the proton’s internal arrangement is modified. More precise measurements at RHIC and other high-energy facilities could reveal whether baryon number follows specific gluonic configurations, how it is redistributed in quark-gluon plasma and whether similar transport occurs in other baryons. As Wenliang Li notes in an accompanying Perspective, identifying whether quarks, gluons or a combination of both transport baryon number could expose hidden aspects of the proton’s identity. What began as a question about a tiny subatomic particle may ultimately help explain how the strong force organizes stable matter across the Universe.

Subject of Research: The transport and origin of baryon number inside the proton, with a focus on the baryon junction model and gluonic contributions to proton structure.

Article Title: Tracking the baryon number with nuclear collisions

News Publication Date: 13-Aug-2026

Web References: https://doi.org/10.1126/science.ads5962

References: Science, “Tracking the baryon number with nuclear collisions,” DOI: 10.1126/science.ads5962

Keywords

Baryon number, proton structure, baryon junction, gluons, quarks, quantum chromodynamics, RHIC, STAR Collaboration, heavy-ion collisions, quark-gluon plasma, nuclear physics, antimatter asymmetry

The brilliance of this new research lies in its audacious approach: framing the complex quantum mechanical process of neutrino oscillations as a problem of managing and quantifying quantum information. Instead of solely focusing on the probabilistic wave functions that describe neutrino states, the study delves into concepts like entanglement, coherence, and information flux. Imagine information as a resource, akin to energy or matter, that can flow, be created, destroyed, or transferred. The researchers propose that the oscillations of neutrinos represent a dynamic interplay and evolution of quantum information carried by these elusive particles. This novel perspective allows for a more nuanced and quantitative analysis of the oscillation process, moving beyond simply predicting the probability of flavor change to understanding the underlying mechanisms of information transfer. This conceptual shift promises to provide unprecedented insights into the quantum nature of these fundamental particles.

At the heart of this groundbreaking work is the concept of quantum coherence, a delicate property that allows quantum particles to exist in multiple states simultaneously. As neutrinos travel through space or matter, their coherence can be affected by various interactions. The study meticulously analyzes how this coherence, which directly relates to the amount of usable quantum information a system holds, evolves during the oscillation process. They are essentially tracing the quantum information “fingerprint” of a neutrino as it transitions between flavors. By quantifying the preservation or degradation of this coherence, scientists can gain a deeper understanding of how the quantum state of a neutrino is affected by its environment and its own internal dynamics. This echoes explorations in quantum computing, where maintaining coherence is paramount for successful computations, suggesting a potential link between our understanding of fundamental particle physics and emerging quantum technologies.

Furthermore, the researchers employ the notion of quantum entanglement, another cornerstone of quantum mechanics where particles become intrinsically linked, sharing a common fate regardless of the distance separating them. While direct entanglement between individual neutrinos during oscillation might seem counterintuitive, the framework developed in this paper suggests more subtle forms of entanglement or correlations that manifest during the process. This could involve entanglement with the surrounding quantum vacuum or with the particles that mediate the weak force responsible for neutrino interactions. Understanding these potential correlations could reveal hidden symmetries and interactions within the quantum field that are responsible for neutrino oscillations, areas that have remained elusive for conventional theoretical approaches.

The study introduces sophisticated mathematical formalisms to quantify the “flow” of quantum information during neutrino oscillations. This involves developing metrics to measure how information is transferred, whether it’s lost, gained, or transformed as a neutrino propagates. This is a radical departure from traditional approaches that primarily focus on the probabilities of detecting a certain flavor state at a given time and location. By treating quantum information as a tangible entity, the researchers aim to create a more complete picture of the oscillation phenomenon, akin to understanding the full information content and dynamics of a complex system rather than just its macroscopic behavior. This quantitative approach to information dynamics could have far-reaching implications for various fields of physics.

One of the most tantalizing implications of this research is its potential to shed light on the origin of mass for elementary particles. The Standard Model of particle physics, while incredibly successful, has limitations, particularly in explaining why neutrinos have mass, and why their masses are so much smaller than those of other fundamental particles like electrons or quarks. The dynamics of quantum information during neutrino oscillations, as explored in this study, might hold clues to the underlying mechanism responsible for generating neutrino mass, possibly involving interactions with new, yet undiscovered fields or particles. This could be a crucial step towards a more unified and complete theory of fundamental forces and particles.

The study also touches upon the delicate balance between quantum information and decoherence. Decoherence is the process by which quantum systems lose their quantum properties and start behaving classically due to interactions with their environment. In the context of neutrino oscillations, understanding how environmental factors or the interactions themselves contribute to decoherence is vital. This research goes beyond simply observing decoherence; it quantics it as a process that influences the informational content of the neutrino, potentially limiting the precision with which we can track its flavor transformations or infer its underlying properties. This has practical implications for future neutrino detection experiments, guiding strategies to minimize environmental noise.

The significance of this work extends beyond theoretical physics, potentially impacting the development of future quantum technologies. The insights gained from studying neutrino oscillations as a quantum information processing system could inspire new methods for quantum sensing or quantum communication. For instance, if neutrinos can be manipulated to encode and carry quantum information across vast distances, understanding their oscillatory behavior could lead to novel strategies for secure quantum communication networks. The very principles that govern their flavor changes might be harnessed for advanced quantum information transfer protocols, extending the reach of quantum phenomena into previously unimaginable domains.

The researchers meticulously detail the mathematical framework employed, which likely involves advanced concepts from quantum information theory, such as quantum entropy, mutual information, and different measures of quantum correlations. These techniques allow for the precise quantification of information transfer and transformation. For example, they might be calculating the change in Shannon entropy related to the flavor states or employing entanglement entropy to probe hidden quantum correlations. This rigorous mathematical approach is what elevates the study from speculative ideas to a robust scientific investigation, providing testable predictions and a solid theoretical foundation for further exploration.

The implications for cosmology are equally profound. Neutrinos are thought to have played a significant role in the early universe, influencing its evolution. The precise dynamics of their oscillations, informed by quantum information principles, could offer new perspectives on cosmic evolution, the formation of large-scale structures, and the nature of dark matter. Understanding how quantum information is processed and conserved during these early cosmic epochs might reveal fundamental properties of the universe that are currently hidden from our view, potentially offering explanations for observed cosmological puzzles.

Moreover, the study provides a novel angle to investigate potential violations of fundamental symmetries in nature. Explaining neutrino oscillations within the Standard Model requires extensions, such as the existence of neutrino masses and mixing. The quantum information perspective could offer a unique way to probe for subtle anomalies or deviations from predicted behavior that might point towards new physics, such as violations of charge-parity (CP) symmetry, which is crucial for understanding the matter-antimatter asymmetry in the universe.

The computational effort involved in such an analysis is likely immense, requiring sophisticated simulations and numerical methods to model the complex quantum dynamics. The authors’ ability to translate abstract quantum information concepts into a framework that can be computationally explored highlights the maturity of both quantum information theory and computational physics. This interdisciplinary approach is becoming increasingly vital for tackling the most challenging scientific questions, bridging the gap between theoretical elegance and empirical verification.

Ultimately, this research represents a paradigm shift in how we approach the study of fundamental particles. By reframing neutrino oscillations as a problem of quantum information dynamics, the study opens up exciting new avenues for theoretical exploration and experimental verification. It underscores the profound interconnectedness of quantum mechanics, particle physics, and information science, suggesting that the universe’s fundamental workings are deeply intertwined with the principles of information processing at its most basic level, a prospect that is as awe-inspiring as it is scientifically significant.

The quest to understand neutrino oscillations has long been a frontier of modern physics, driven by their potential to reveal physics beyond the Standard Model and offer insights into some of the universe’s most enduring mysteries. This latest work, by ingeniously applying the sophisticated tools of quantum information theory, promises to unlock deeper secrets of these ethereal particles. It’s a testament to the power of interdisciplinary research, where concepts from seemingly disparate fields converge to illuminate complex phenomena, pushing the boundaries of our cosmic comprehension and potentially paving the way for future technological revolutions rooted in the quantum realm.

Subject of Research: Dynamics of quantum information resources in two-flavor neutrino oscillations.

Article Title: Dynamics of quantum information resources in two-flavor neutrino oscillations.

Article References: El Bouzaidi, K., Slaoui, A., Drissi, L.B. et al. Dynamics of quantum information resources in two-flavor neutrino oscillations. Eur. Phys. J. C 85, 1349 (2025).

Image Credits: AI Generated

DOI: https://doi.org/10.1140/epjc/s10052-025-15083-z

Keywords: Neutrino oscillations, quantum information, quantum entanglement, quantum coherence, quantum mechanics, particle physics, Standard Model, quantum information theory, flavor transformation, physics beyond the Standard Model