High-energy heavy ion collisions reveal subtleties of nuclear structure at US lab
Scientists used high-energy heavy ion collisions to reveal subtle details about the shapes of atomic nuclei.
They demonstrated the new way to use high-energy p smashups at the Relativistic Heavy Ion Collider (RHIC), a world-class p accelerator at Brookhaven National Laboratory. Scientists claimed that the new measurement not only quantifies the overall shape of the nucleus — whether it's elongated like a football or squashed down like a tangerine — but also the subtle triaxiality, the relative differences among its three principle axes that characterize a shape in between the 'football' and 'tangerine.
Robust way to image nuclear structure
Published in a paper in Nature, the method is claimed to be complementary to lower energy techniques for determining nuclear structure. It will add depth to scientists' understanding of the nuclei that make up the bulk of visible matter. "The best way to demonstrate the robustness of nuclear physics knowledge gained at RHIC is to show that we can apply the technology and physics insights to other fields," said Jiangyong Jia, a professor at Stony Brook University (SBU) who has a joint appointment at Brookhaven Lab and is one of the principal authors on the STAR Collaboration publication. "Now that we've demonstrated a robust way to image nuclear structure, there will be many applications."
Deciphering nuclear shapes has relevance to a wide range of physics questions
Scientists claimed that deciphering nuclear shapes has relevance to a wide range of physics questions, including which atoms are most likely to split in nuclear fission, how heavy atomic elements form in collisions of neutron stars, and which nuclei could point the way to exotic p decay discoveries. Leveraging improved knowledge of nuclear shapes will also deepen scientists' understanding of the initial conditions of a p soup that mimics the early universe, which is created in RHIC's energetic p smashups, said a press release . The method can be applied to analyzing additional data from RHIC as well as data collected from nuclear collisions at Europe's Large Hadron Collider (LHC). It will also have relevance to future explorations of nuclei at the Electron-Ion Collider, a nuclear physics facility in the design stage at Brookhaven Lab.
"Ultimately, since 99.9% of the visible matter that people and all the stars and planets of the cosmos are made of resides in the nuclei at the center of atoms, understanding these nuclear building blocks is at the heart of understanding who we are," added the press release.
Method can be used to determine shapes of other nuclei
Researchers maintained that the method can also be used to determine shapes of other nuclei, especially those where the low-energy experiments yielded limited understanding.
example would be to apply the method to so-called isobar nuclei — nuclei with the same total number of protons and neutrons (nucleons), but different proportions of each type, according to researchers.
Such pairs are involved when two neutrons in a higher-neutron-number "parent" nucleus transform into protons via a nuclear weak decay process to create the lower-neutron-number "daughter" — a process known as double beta decay, claimed researchers.
They stressed that knowing the shape differences between parent and daughter nuclei could help reduce model uncertainties in experiments searching for an unseen type of decay known as neutrinoless double beta decay.
