Researchers from the Niels Bohr Institute, together with colleagues from the international ALICE collaboration, have come one step closer to understanding matter from the Universe’s first millionth of a second, challenging previous assumptions about how to simulate the Big Bang. By colliding oxygen-16 and neon-20 nuclei at CERN, researchers succeeded in creating the primordial matter, thought to be the earliest form of matter, using significantly smaller nuclei than previously believed possible.
“We have pushed the boundary for how small the atomic nuclei can be while still recreating this primordial matter – what you could call a Little Big Bang,” says Associate Professor You Zhou, who led the experiment. Analyzing particle movement after these collisions revealed the shape of the original nuclei, offering new insights into nuclear physics and the Universe’s origins.
Oxygen-16 and Neon-20 Collisions Recreate Early Universe Matter
The geometric shape of atomic nuclei directly influences the particles created in high-energy collisions, a finding that refines understanding of the Universe’s earliest moments. Researchers discovered that collisions involving oxygen-16 and neon-20 nuclei produce distinct patterns of particle movement, revealing information about the nuclei’s form during the fleeting existence of quark-gluon plasma. While oxygen nuclei yield a more rounded pattern after collision, neon nuclei create a pattern resembling bowling pins, a difference directly linked to their initial shapes.
If the two nuclei we smash together are spherical, we get one pattern. If they are shaped like bowling pins, we get another,” explained a researcher. The CERN facility’s Large Hadron Collider enabled these collisions, providing the energy needed to briefly simulate the extreme temperatures present after the Big Bang. Researchers from the Niels Bohr Institute, together with colleagues from the international ALICE collaboration, have come one step closer to understanding them.
Analyzing the resulting particle trajectories allows physicists to indirectly “see” the shape of the colliding nuclei, a technique likened to observing a shadow to discern an object’s form. “It is a bit like shining light on an object and seeing its shadow. You cannot see the object directly, but its shadow reveals its shape.
In the same way, the movement of the particles reveals the geometric shape of the atomic nuclei that was present at the beginning of the collision,” a researcher stated. This method offers a novel approach to studying nuclear structure, complementing traditional low-energy investigations and providing insights into the strong force governing these interactions, ultimately helping to understand how the initial plasma evolved into the matter composing everything around us.
What is fascinating is that we can use the same experiment both to learn about the structure of atomic nuclei and to gain a better understanding of what happened during the birth of the Universe. These two things turn out to be much more closely connected than one might initially think.
You Zhou, Associate Professor
Quark-Gluon Plasma Formation with Reduced Atomic Nuclei
The ability to discern the shape of colliding nuclei stems from analyzing the resulting particle trajectories, a technique previously limited to heavier nuclei. Researchers from the Niels Bohr Institute, together with colleagues from the international ALICE collaboration, have now succeeded in creating the primordial matter by smashing oxygen-16 and neon-20 nuclei together, challenging the long-held assumption that lead nuclei were necessary for its formation. This achievement opens new avenues for investigating the strong force and the earliest moments of the Universe using smaller, more manageable systems.
This novel approach relies on interpreting the movement patterns of particles emitted after the collisions; these patterns indirectly reveal the geometry of the original nuclei. The implications extend beyond nuclear physics, offering a unique connection between the microscopic structure of nuclei and the conditions of the early Universe. “What is fascinating is that we can use the same experiment both to learn about the structure of atomic nuclei and to gain a better understanding of what happened during the birth of the Universe.
These two things turn out to be much more closely connected than one might initially think,” Zhou adds. Future experiments will explore even lighter nuclei, such as helium-4, to further refine the boundary conditions for quark-gluon plasma creation and deepen our understanding of the primordial matter that once filled the cosmos.
We have pushed the boundary for how small the atomic nuclei can be while still recreating this primordial matter – what you could call a Little Big Bang. We now know more about the fundamental conditions required for matter to transition into this extreme state.
Associate Professor You Zhou, who led the experiment and until recently was employed at the Niels Bohr Institute at the
Bowling-Pin Shape Reveals Nuclei Geometry in Collisions
Collisions involving neon-20 nuclei consistently produce a distinct, bowling-pin-shaped pattern in the resulting particle trajectories, a contrast to the more rounded patterns observed when colliding oxygen-16 nuclei. Researchers at the Niels Bohr Institute, together with colleagues from the international ALICE collaboration, cannot directly observe the fleeting quark-gluon plasma formed in these collisions, but instead interpret the dispersal of particles emerging from it as a reflection of the original nuclei’s form.
This approach builds on the legacy of Aage Bohr, whose work on nuclear structure earned him the 1975 Nobel Prize in Physics. Understanding nuclear shape is not simply a matter of geometry; it provides important information about how protons and neutrons organize themselves and, critically, how the strong force operates within the nucleus. Previously, investigations into nuclear structure largely focused on low-energy studies of nuclear rotation and vibration, but this new method offers a complementary perspective through ultra-high energy collisions. Macquarie University builds chips for CERN’s hunt for universe origins.
The particles from the primordial matter are directly governed by the geometric shape of the atomic nucleus. If the two nuclei we smash together are spherical, we get one pattern. If they are shaped like bowling pins, we get another. By studying how the particles move after the collision, we can gain insights into atomic nuclei that are otherwise difficult for physicists to obtain.
Emil Gorm Dahlbæk Nielsen, Postdoctoral Researcher
Niels Bohr Institute Extends Legacy of Nuclear Structure Research
Recent analysis of particle movement following collisions at CERN reveals that neon-20 nuclei consistently exhibit a bowling-pin shape, a pattern previously unexpected in the creation of quark-gluon plasma. This finding challenges the long-held assumption that creating this plasma required collisions between very heavy atomic nuclei such as lead. Associate Professor You Zhou, formerly of the Niels Bohr Institute at the University of Copenhagen, led the experiment that produced these results as part of the international ALICE collaboration, recently publishing the findings in Physical Review Letters.
The ability to recreate quark-gluon plasma using lighter nuclei expands the scope of research into the earliest moments of existence, offering a new avenue for understanding the evolution of matter. This approach allows scientists to probe fundamental conditions governing the transition of matter into this extreme state, potentially providing new knowledge about the Universe’s initial formation. Postdoctoral Researcher Emil Gorm Dahlbæk Nielsen from the Niels Bohr Institute explains that analyzing particle trajectories after these collisions provides a unique method for determining the shape of atomic nuclei.
A precise understanding of nuclear structure helps us understand the strong force. But instead of carefully investigating nuclei at low energies, we smash them together at the highest energies we can create and can now read their shape from the imprint they leave behind.
You Zhou, Associate Professor
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