Imaging Nuclear Shapes by Smashing Them to Smithereens

Study co-authors Jiangyong Jia and Shengli Huang in front of the STAR detector at RHIC. Photo by Kevin Coughlin/Brookhaven National Laboratory.

SBU scientists use heavy ion collisions to reveal subtleties of nuclear structure with implications for many areas of physics

Stony Brook University scientists have demonstrated a new way to use high-energy particle smashups at the Relativistic Heavy Ion Collider (RHIC) at Brookhaven National Laboratory (BNL) to reveal subtle details about the shapes of atomic nuclei.

The method, described in a paper just published in Nature, is complementary to lower energy techniques for determining nuclear structure, and will add depth to scientists' understanding of the nuclei that make up the bulk of visible matter.

"In this new measurement, we not only quantify 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,'" said Jiangyong Jia, adjunct professor in the Department of Physics and Astronomy who has a joint appointment at BNL and is one of the principal authors on the STAR Collaboration publication.

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 particle decay discoveries.

Leveraging improved knowledge of nuclear shapes will deepen scientists' understanding of the initial conditions of a particle soup that mimics the early universe, which is created in RHIC's energetic particle smashups. 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 BNL. RHIC is a U.S. Department of Energy (DOE) Office of Science user facility for nuclear physics research.

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.

"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," Jia said. "Now that we've demonstrated a robust way to image nuclear structure, there will be many applications."

STAR scientists analyzed the flow and momentum of particles emerging from collisions and compared them with models of hydrodynamic expansion for different quark-gluon plasma (QGP) shapes to arrive at the shapes of the originally colliding nuclei. To show their method worked, they compared central collisions of gold nuclei - which are believed, from low energy studies, to be close to spherical - with central collisions of uranium nuclei, which have a pronounced elongated football-like shape. Because the gold nuclei are nearly spherical, there shouldn't be much variation from collision to collision in the flow patterns of emitted particles.

Read the complete story at the BNL website.

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