Large Hadron Collider Detects Bowling Pin-Shaped Atomic Nuclei

Scientists operating the Large Hadron Collider (LHC) at CERN have uncovered compelling evidence suggesting that the atomic nucleus of neon is not spherical, but rather possesses a distinct shape resembling a bowling pin. This groundbreaking discovery, made by the CMS Collaboration, challenges traditional textbook depictions of atomic nuclei and opens new avenues for understanding nuclear physics, particularly the behavior of matter forged in high-energy particle collisions.

For decades, atomic nuclei have been commonly illustrated as round, dense spheres. However, this simplified model doesn't capture the full complexity of nuclear structures. Just as some atoms deviate from perfect spheres, exhibiting shapes like pears, neon's nucleus appears to adopt a more complex form. Understanding these non-spherical shapes is crucial for predicting how atomic nuclei will behave under extreme forces.

Visualizing the precise shape of an atomic nucleus is a significant challenge due to their minuscule size and quantum properties. In standard observations, a nucleus's quantum state averages out its potential orientations, making even a non-spherical nucleus appear spherical. This is where the immense power of particle colliders like the LHC becomes indispensable. By colliding nuclei at nearly the speed of light, physicists can infer their intrinsic structure from the resulting patterns of ejected particles.

Probing Nuclear Geometry Through Collisions

The CMS Collaboration conducted experiments comparing collisions involving oxygen-16 and neon-20 nuclei. While not directly smashing oxygen into neon, they analyzed the outcomes of separate oxygen-oxygen and neon-neon collisions. The choice of these elements is significant because while they are similar in mass, their predicted internal structures differ substantially. Theoretical models and prior research suggest oxygen-16 nuclei possess a tetrahedral shape, whereas neon-20 nuclei are predicted to resemble a bowling pin.

Researchers meticulously analyzed the flow of particles emerging from these high-energy collisions. They looked for specific directional patterns, such as elliptic and triangular flow, which are indicators of the initial geometry of the colliding nuclei. The hypothesis was that if the underlying nuclear structures were indeed different, subtle but detectable variations would manifest in these flow patterns. Specifically, differences in the strength of elliptic flow, particularly in head-on collisions, were expected to correlate with the nuclei's shapes.

The experimental results showed promising indications. While quantitative discrepancies were observed between measured triangular flow patterns and theoretical predictions, the overall findings strongly support the sensitivity of particle flow to nuclear geometry. This means that the arrangement of protons and neutrons within an atomic nucleus can leave a discernible signature in the complex spray of particles produced during collisions. This discovery suggests that particle colliders can serve as powerful tools for probing the intricate structures of atomic nuclei.

The research team stated in their findings, "These results establish the sensitivity of collective flow in light ion collisions to both the initial geometry and the hydrodynamic medium response." They further noted that the study "provide[s] stringent constraints on models of small-system collectivity and offer valuable implications for nuclear structure studies." This work could revolutionize how scientists study the fundamental building blocks of matter.