For decades, physicists have grappled with a puzzling question: How can we reconcile the two different pictures we have of the atomic nucleus?
On one hand, we see nuclei as collections of protons and neutrons. On the other, at higher energies, they appear as a sea of quarks and gluons.
This disparity has been a sticking point in nuclear physics, but a recent development might just have the answer.
High-tech, innovative approach
One physicist determined to solve this mystery is Dr. Aleksander Kusina, a theoretician from the Nuclear Physics Institute of the Polish Academy of Sciences .
He's part of an international team that's been working tirelessly to bring these two worlds together. With over 20 years in the field, Dr. Kusina has dedicated his career to understanding the fundamental aspects of matter.
Alongside fellow scientists from the international nCTEQ collaboration on quark-gluon distributions, Dr. Kusina and his colleagues have achieved something remarkable.
They've managed to reproduce the properties of atomic nuclei using quark-gluon models , something that had eluded physicists for years.
Mystery of atomic nuclei
But why has this been such a tough nut to crack? At low energies, atomic nuclei behave as if they're made up of protons and neutrons -- particles we can detect and study.
These particles were discovered almost a century ago and were once thought to be indivisible. However, as scientists probed deeper, they realized there was more to the story.
Protons, neutrons, quarks, and gluons
Back in the 1960s, scientists proposed that protons and neutrons weren't indivisible after all. They suggested that inside these particles were even smaller components -- quarks held together by gluons.
This idea was confirmed through high-energy experiments, where particles were smashed together at incredible speeds.
At these energies, the internal structure of protons and neutrons becomes apparent, revealing the quarks and gluons within.
Combining two models
Despite knowing about quarks and gluons for decades, integrating them fully into our understanding of atomic nuclei proved challenging.
Models based on protons and neutrons worked well at low energies, while quark-gluon models were effective at high energies.
But bringing the two together into a single, coherent picture was like trying to fit a square peg into a round hole.
"Until now, there have been two parallel descriptions of atomic nuclei, one based on protons and neutrons which we can see at low energies, and another, for high energies, based on quarks and gluons," says Dr. Kusina. "In our work, we have managed to bring these two so far separated worlds together."
Role of parton distribution functions
The team's approach was to extend parton distribution functions (PDFs), which are used to describe how quarks and gluons are distributed inside protons and neutrons.
They drew inspiration from nuclear models used for low-energy collisions, where protons and neutrons form strongly interacting pairs.
Parton distribution functions are essential tools in high-energy physics . They provide a probabilistic description of the momentum and spin of quarks and gluons inside a proton or neutron.
By adjusting these functions, physicists can predict the outcomes of high-energy collisions, like those occurring in particle accelerators.
Nucleon pairing at the parton level
From a theoretical standpoint, the team's innovation was to simulate the phenomenon of nucleon pairing at the parton level.
In low-energy nuclear physics, it's well-known that protons and neutrons can pair up, affecting the behavior of the nucleus .
By incorporating this effect into the PDFs, the team was able to bridge the gap between the two models.
"In our model, we made improvements to simulate the phenomenon of pairing of certain nucleons," explains Dr. Kusina. "This is because we recognized that this effect could also be relevant at the parton level."
Better atomic nucleus alignment
This novel approach allowed the researchers to determine, for 18 different atomic nuclei, the parton distribution functions in atomic nuclei, parton distributions in correlated nucleon pairs, and even the numbers of such correlated pairs.
Their results confirmed that most correlated pairs are proton-neutron pairs, which is particularly interesting for heavy nuclei like gold or lead.
Another advantage of their method is that it provides a better description of experimental data than traditional models. By aligning theoretical predictions with actual observations, the team has strengthened the validity of their approach.
"Interestingly, this allowed for a conceptual simplification of the theoretical description, which should in future enable us to study parton distributions for individual atomic nuclei more precisely," says Dr. Kusina.
Why does this matter?
So, what does all this mean for the field of nuclear physics? By successfully combining the two models, the team has opened the door to a unified understanding of atomic nuclei.
This could have far-reaching implications, from refining our knowledge of fundamental forces to impacting practical applications like nuclear energy .
Understanding the structure of atomic nuclei is crucial for many areas of science and technology. It influences how we model nuclear reactions, how we develop medical imaging techniques, and even how we approach the search for new materials.
Unified picture of the atomic nucleus
This breakthrough isn't just a win for theoretical physics. It sets the stage for future research that could delve even deeper into the mysteries of matter.
With this new approach, scientists can explore the nuances of nucleon interactions and parton distributions in ways that were previously out of reach.
Moreover, it could help in interpreting data from current and future particle accelerators. As we push the boundaries of high-energy physics, having a unified model of atomic nuclei becomes increasingly important.
"Science is a team effort," says Dr. Kusina. "By working together, we can achieve things that would be impossible alone."
The full study was published in the journal Physical Review Letters .
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