Pear-shaped Atoms Test Standard Model of Physics, Offers Big Bang Clues

An international team of researchers has found direct evidence of pear-shaped nuclei in atoms. It might not seem like much, but it could be big news, as the discovery that some atoms' nuclei can be lopsided not only contributes to the canon of science, but also challenges the Standard Model of particle physics.

The findings could advance the search for a new fundamental force in nature that could explain why there is more matter than antimatter, according to University of Michigan physicist Tim Chupp, who co-authored the paper on the find.

"If equal amounts of matter and antimatter were created at the Big Bang, everything would have annihilated, and there would be no galaxies, stars, planets or people," said Chupp, in a UM news release.

Chupp said the pear shape is special because it means the protons and neutrons, which compose the nucleus, are in slightly different places along an internal axis.

In the pear-shaped nuclei, nuclear forces push protons away from the center of the atom, making them lopsided.

Most nuclei that exist naturally are basically spherical or rugby-ball shaped, but the new research from the CERN facility suggests that some atoms are lopsided like pears, with more mass at one end than the other. The experimental observations at CERN will help physicists better understand the theory of nuclear structure and help refine searches for electric dipole moments (EDM) in atoms.

The Standard Model of particle physics predicts that the value of the EDM is so small that it cannot be observed. However there are many theories that suggest that there is a way to measure the EDM. The pear-shaped atom gives physicists the best known example to test these theories and get closer to obtaining observable measurements of the EDM.

"Our findings contradict some nuclear theories and will help refine others. The measurements will also help direct the searches for atomic EDMs currently being carried out in North America and in Europe, where new techniques are being developed to exploit the special properties of radon and radium isotopes," said Peter Butler, the physicist from the University of Liverpool who carried out the measurements and led the research.

"Our expectation is that the data from our nuclear physics experiments can be combined with the results from atomic trapping experiments measuring EDMs to make the most stringent tests of the Standard Model, the best theory we have for understanding the nature of the building blocks of the universe," Butler said in a release from University of Liverpool.

The pear shape was observed in two sort-lived isotopes, 220Rn and 224Ra, after using the particle accelerator to blast the atoms at eight percent of the speed of light. The data show that while 224Ra is pear-shaped, 220Rn does not assume the fixed shape of a pear but rather vibrates about this shape.

With two known pear-shaped nuclei, physicists can now start to tease apart the theoretical models and further our understanding of particle physics.

The findings are published in Nature in a paper called "Studies of nuclear pear-shapes using accelerated radioactive beams."

The photo above shows a graphical representation of the pear-shaped nucleus of an exotic atom, the video below animates the object.