At the heart of our understanding of matter lies the proton, a seemingly simple particle that plays an indispensable role in the atomic nucleus. Yet, as scientists delve deeper into the proton’s constitution, they find that it is much more complicated than it appears. At the core of the proton are quarks and gluons—tiny particles that interact in ways that are still not fully understood. A group of dedicated researchers known as the HadStruc Collaboration explores this intricate world, striving to map out the myriad interactions among these fundamental constituents. By employing sophisticated mathematical models and high-performance computing, the collaboration aims to illuminate the underlying dynamics that govern the proton’s structure and behavior.
Partons, the collective term for quarks and gluons, are the building blocks of hadrons. Hadrons include all particles made up of quarks, with the proton being one of the most abundant. The strong nuclear force binds these partons, creating a dynamic and ever-shifting landscape. Joseph Karpie, a postdoctoral researcher at the Thomas Jefferson National Accelerator Facility, emphasizes the importance of understanding how these interactions manifest within the proton. Despite significant strides in particle physics, the precise distribution and behavior of quarks and gluons remain elusive, sparking ongoing investigation.
To tackle the complexities of proton structure, the HadStruc team employs a mathematical framework called lattice quantum chromodynamics (QCD). This approach, when executed on high-performance supercomputers, enables researchers to simulate and visualize particle interactions in a three-dimensional context. Hervé Dutrieux, a postdoctoral researcher involved in the collaboration, articulates how generalized parton distributions (GPDs) enhance our understanding compared to traditional one-dimensional parton distribution functions (PDFs). GPDs offer a more comprehensive view of the internal structure of protons and shed light on critical questions concerning their spin.
One of the notable challenges in proton research is the spin crisis, a term that describes the surprising finding that quarks contribute less than half of the proton’s overall spin. This revelation challenges physicists to consider the contributions from gluons and the orbital angular momentum of partons. The intricate relationships between these factors are high on the research agenda for the HadStruc Collaboration. Dutrieux notes that GPDs present an exciting possibility to delve into these questions and contribute vital insights into how spin and momentum are distributed within the proton.
The collaboration’s efforts are underpinned by an enormous amount of computational work. Researchers have conducted over 65,000 simulations to ensure the veracity of their mathematical models. Utilizing supercomputers like Frontera at the Texas Advanced Computer Center and the Frontier supercomputer at Oak Ridge National Laboratory, the collaboration has engaged numerous processors in simulations that demanded millions of computational hours. This meticulous process has yielded promising results, forming a robust foundation for future studies.
The scientific community is particularly enthusiastic about the prospects of translating theoretical work into practical experimentation. The HadStruc Collaboration’s findings are already set to be tested in high-energy facilities around the world. Both deeply virtual Compton scattering and deeply virtual meson production experiments will be conducted at Jefferson Lab and various other locations. As Karpie points out, the collaboration anticipates that its theoretical advancements will align with ongoing experimental data collection, serving to refine and expand their models.
Additionally, there is immense anticipation surrounding the Electron-Ion Collider (EIC), which is being constructed at the Brookhaven National Laboratory. This revolutionary particle accelerator will provide unprecedented capabilities to probe hadronic structures, enabling researchers to extend their investigations into realms that current technologies cannot access.
As the HadStruc Collaboration continues its exploration of proton structure, it recognizes the need to advance beyond mere retrospective analysis. Historically, quantum chromodynamics has often lagged behind empirical findings, and the researchers are keen to shift that dynamic. By enhancing their models and refining predictions, the team hopes to stay one step ahead of experimental outcomes and deepen our understanding of the proton.
The intricate tapestry of quarks, gluons, and their interactions within hadrons represents one of the most challenging yet fascinating areas of modern physics. Through innovative approaches and cutting-edge technology, the HadStruc Collaboration stands at the forefront of this scientific frontier, eager to unearth the secrets of matter at its most fundamental level.