At the subatomic level, the notion of solid matter collapses under the weight of complexity. Within hadrons—protons and neutrons that constitute the nucleus of an atom—lies a chaotic amalgamation of quarks and gluons. These particles, collectively referred to as partons, are not mere constituents; they are dynamic players in a dance dictated by the strong force, one of nature’s four fundamental forces. The HadStruc Collaboration, a consortium of nuclear physicists, has embarked on a groundbreaking journey to elucidate the formation and interaction of these partons. Based at the Thomas Jefferson National Accelerator Facility (Jefferson Lab), this interdisciplinary group integrates expertise from several academic institutions to develop a sophisticated mathematical framework aimed at understanding hadronic structure.
Joseph Karpie, a postdoctoral researcher within the HadStruc Collaboration, highlights the team’s mission: to uncover the distributions and interactions of quarks and gluons inside protons. Utilizing lattice quantum chromodynamics (QCD), the physicists aim to construct a detailed portrait of the proton, moving away from traditional methods that offer a limited, one-dimensional perspective. Instead, the group has proposed a three-dimensional approach through the lens of generalized parton distributions (GPDs). This innovative framework not only expands the analytical horizon but also lays the groundwork for tackling some of the pressing questions surrounding proton spin—a mystery that has puzzled scientists since experimental evidence revealed in 1987 that quarks contribute less than half of the proton’s total spin.
The innovative use of GPDs facilitates a more nuanced understanding of how the proton’s spin emerges. Dutrieux, another member of the collaboration, underscores the advantages of GPDs over one-dimensional parton distribution functions (PDFs). This shift in perspective allows researchers to analyze various domains of the proton’s interior, including contributions from gluons and orbital angular momentum, which account for the remaining portion of the proton’s spin. This associative understanding could significantly enrich our grasp of proton dynamics, prompting further inquiries into the fabric of matter.
In addition to exploring spin dynamics, the HadStruc Collaboration focuses on the energy-momentum tensor, a critical component that reveals how energy and momentum are allocated within the proton. Gaining insights into this tensor could illuminate the proton’s interactions with gravity and expand our understanding of fundamental forces. Delving into these calculations demands the power of advanced supercomputers, as the complexity of quantum chromodynamics requires robust computational resources to yield meaningful results.
The collaborative effort has led to astounding computational achievements. Over 65,000 simulations tested their new theoretical framework and facilitated a rigorous evaluation of assumptions. Conducted on state-of-the-art facilities, including Frontera at the Texas Advanced Computer Center and the Frontier supercomputer at Oak Ridge National Laboratory, these massive undertakings required millions of hours of collective processing time. The results generated from these simulations are poised to contribute significantly to the field of quark-gluon tomography (QGT)—a sub-discipline focused on visualizing the internal structure of hadrons.
The promise of the HadStruc Collaboration extends beyond theoretical work. Their insights are finding practical applications in high-energy experimental facilities that are currently poised to advance our understanding of hadronic structures. Developments at Jefferson Lab and other institutions include investigating hadron structure through processes like deeply virtual Compton scattering (DVCS) and deeply virtual meson production (DVMP). The Electron-Ion Collider (EIC), an upcoming particle accelerator at Brookhaven National Laboratory, is also expected to leverage these theoretical advancements, enabling physicists to probe deeper into hadronic structures than ever before.
Moreover, Karpie expresses the ambition of anticipating experimental trends, rather than merely reacting to them. Historically, the field of quantum chromodynamics has often been seen as trailing behind experimental discoveries, engaging in “post-dicting” rather than “predicting.” The HadStruc team seeks to reverse this trend by developing predictive models that will inform future discoveries and lead the path in hadrons research.
The exploration of partons within hadrons ignites a fascinating journey into the heart of matter. The HadStruc Collaboration’s groundbreaking work exemplifies the intersection of computational prowess and theoretical insight, pushing the boundaries of what we know about protons and neutrons. As researchers unravel the intricacies of quark-gluon interactions and advance our understanding of the fabric of the universe, we find ourselves not only witnessing a scientific evolution but also laying the groundwork for a future where the mysteries of matter may finally be revealed. The legacy of this collaboration is poised to resonate well beyond its immediate findings, inspiring generations of physicists to delve into the enigmatic world of particles that build the very essence of our reality.
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