Nuclear physicists at the Thomas Jefferson National Accelerator Facility have observed the production of lambda particles, also known as “strange matter,” through semi-inclusive deep inelastic scattering for the first time ever. The experiment sheds light on the process of forming strange matter from ordinary matter and shows that the building blocks of protons, quarks, and gluons can sometimes march through the nucleus of an atom in pairs referred to as diquarks. The analysis suggests that the current theory used to describe the strong interaction between these particles may be incomplete.
Nuclear physicists at the Thomas Jefferson National Accelerator Facility have observed the production of lambda particles, also known as “strange matter,” for the first time ever. The experiment sheds light on the process of forming strange matter from ordinary matter and suggests that the current theory used to describe the strong interaction between these particles may be incomplete.
The story of the discovery of strange matter by nuclear physicists at Jefferson Laboratory is a tale of hard work and dedication spanning over a decade. The findings have challenged the current understanding of the strong interaction between particles and opened up new avenues for research in this field.
The Formation of Strange Matter
The experiment was carried out by shooting the Continuous Electron Beam Accelerator Facility (CEBAF) electron beam at different targets, including carbon, iron, and lead. When a high-energy electron from CEBAF reaches one of these targets, it breaks apart a proton or neutron inside one of the target’s nuclei. After the electron interacts with a quark or quarks via an exchanged virtual photon, the “struck” quark(s) begins moving as a free particle in the medium, typically joining up with other quark(s) it encounters to form a new composite particle as they propagate through the nucleus. And some of the time, this composite particle will be a lambda.
Unlike protons and neutrons, which only contain a mixture of up and down quarks, lambdas contain one up quark, one down quark, and one strange quark. Physicists have dubbed matter that contains strange quarks “strange matter.” But the lambda is short-lived – after formation, it will swiftly decay into two other particles: a pion and either a proton or neutron.
The data that was used in this study was originally gathered in 2004, but it took several years for Lamiaa El Fassi and her group to re-analyze the data and extract these unprecedented measurements. Lamiaa El Fassi, who is currently serving as an associate professor of physics at Mississippi State University and is the lead researcher of this project, initially analyzed these data while she was working on her thesis project to obtain her graduate degree on a different topic.
Nearly a decade after completing her initial research with these data, El Fassi revisited the dataset and led her group through a careful analysis to yield these unprecedented measurements. The dataset comes from experiments in Jefferson Lab’s Continuous Electron Beam Accelerator Facility (CEBAF), a DOE user facility. In the experiment, nuclear physicists tracked what happened when electrons from CEBAF scatter off the target nucleus and probe the confined quarks inside protons and neutrons.
New Insights into Strong Interaction
The experiment has challenged the current theory used to describe the strong interaction between particles. Comparing measurements to models of quantum chromodynamics (QCD)’s predictions allows physicists to test this theory. However, the diquark finding differs from the model’s current predictions, suggesting that something about the model is off.
“There is an unknown ingredient that we don’t understand. This is extremely surprising since the existing theory can describe essentially all other observations, but not this one,” said co-author William Brooks, professor of physics at Federico Santa María Technical University and co-spokesperson of the EG2 experiment. “That means there is something new to learn, and at the moment, we have no clue what it could be.”
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The researchers’ discovery suggests that there may be new phenomena and mechanisms underlying the formation of strange matter from ordinary matter, providing opportunities for future research. The upcoming Electron-Ion Collider (EIC) at DOE’s Brookhaven National Laboratory will provide a new opportunity to continue studying this strange matter and quark pairing structure of the nucleon with greater precision. The research could help us better understand the strong interaction between particles, which has a range of applications, including nuclear energy, nuclear weapons, and medical imaging.
How can you contribute?
The research in this field requires expertise in nuclear physics and particle physics. However, aspiring researchers can also explore this field to gain a better understanding of the strong interaction and contribute to the development of new theories and models. The scientific community also uses various digital tools such as Python libraries, particle tracking software, and data analysis software to analyze and interpret experimental data.