Mapping atoms by crushing them into tiny pieces

07.12.2024.
Mapping atoms by crushing them into tiny pieces
The researchers of the STAR experiment have discovered a new tool to explore the details of nuclear structures in high-energy heavy-ion collisions. This new discovery will impact many areas of physics and, in the long term, various other scientific fields. 

An artistic representation of charged particle trajectories resulting from the collision of two uranium nuclei, illustrated on a schematic of the STAR detector at the Relativistic Heavy Ion Collider (RHIC). The incoming clouds of uranium nuclei approach the collision point at nearly the speed of light, where the collision of a single pair of nuclei can be observed. By analyzing the particle flow patterns from many such collisions, researchers can reconstruct the original shape of the colliding nuclei. (Chunqian Zhang/Fudan University and Jianyang Jia/Stony Brook University) 

As described in a public outreach statement by Brookhaven National Laboratory, researchers use nuclear collisions created in the Relativistic Heavy Ion Collider (RHIC) and studied by the STAR experiment (of which ELTE is an active member) to develop new methods for uncovering fine details of nuclear shapes. The latest method, presented in a study recently published in Nature, complements previously known lower-energy techniques for determining nuclear structure and provides new information about the atomic nuclei that make up a large part of visible material. 

“With this new measurement, we can not only quantitatively describe the general shape of the atomic nucleus—whether it is elongated like an American football or compressed like a tangerine—but also its ‘triaxiality,’ the relative differences between the three principal axes of the ellipsoid shape of the nucleus, which characterize the shape between the football and the tangerine,” said Jianyang Jia, a professor at Stony Brook University and one of the lead authors of the STAR collaboration publication at RHIC. 

ELTE is an official participant in the STAR collaboration. The STAR-ELTE research group operates at the Institute of Physics, in the Department of Atomic Physics (led by Máté Csanád, university professor at the department, who also participated in the internal review and verification of the analysis and the publication based on it). The group is part of the Astrophysics and Particle Physics Research Area within the Themes of Excellence Program. Participation in the STAR experiment is currently supported by the NKFIH OTKA K-138136 and PD-146589 projects. Members of the research group are personally involved in data collection. Additionally, a key task for ELTE researchers is data analysis, particularly focusing on femtoscopy measurements. Máté Csanád was also the director of the experiment's data archiving and is currently a member of the committee coordinating invited lectures for the collaboration. 

As Máté Csanád says: "These interdisciplinary researches showcase the richness of high-energy physics. Our research group's focus is on femtoscopy, which is related to the HBT effect known in astrophysics. We hope that this method will soon prove useful in mapping atomic nuclei as well." 

The central collision of elongated uranium nuclei occurs between two extreme orientations: head-on and tip-to-tip (a), resulting in different arrangements. This leads to the creation of quark-gluon plasma (QGP) with varying shapes and sizes (b), which in turn produces different expansion patterns (c), leading to a varied distribution of emitted particles (d). By measuring the change in these "flow" patterns from one collision to another and comparing them to the collisions of nearly spherical gold nuclei, the shape of the uranium atomic nuclei can be determined. (Jianyang Jia/Stony Brook University) 

Unraveling the shape of atomic nuclei is crucial for many questions in physics, such as determining which atoms are most likely to undergo fission in nuclear reactions, how heavy chemical elements are formed in neutron star collisions, and which nuclei might lead to the discovery of exotic particle decay. A better understanding of nuclear shapes also deepens our knowledge of quark matter, which mimics the early universe. This method can be applied to analyze additional data from RHIC, as well as data from collisions studied at the CERN Large Hadron Collider (LHC), and will also be important for research at the upcoming Electron-Ion Collider (EiC) at Brookhaven National Laboratory. 

Ultimately, since 99.9% of the visible material formed by people and all the stars and planets in the universe is found in the atomic nuclei at the center of atoms, understanding these building blocks lies at the heart of understanding ourselves. 

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