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An unexpected result allows researchers to narrow the scope on the quest for the chiral magnetic effect



A long-awaited quest for the “chiral magnetic effect (CME),” which could explain the dominance of matter over antimatter in our universe, has been released after years of research with the Relativistic Heavy Ion Collider (RHIC), of the U.S. Department of Energy (DOE).  This experiment took place over multiple locations, including Purdue University, and sought to discover evidence of the CME. It is the phenomenon of electric charge separation, due to imbalanced chirality (a term referring to the numbers of left-handed and right-handed particles), along a magnetic field as strong as 1014 Tesla created in relativistic heavy ion collisions at a speed that is 99.995% of the speed of light. 

Results from this study were not as predicted. Initially, researchers expected to reveal the CME, but instead, they learned where better to look for it.  According to Dr. Fuqiang Wang, Purdue University Professor of Physics, this study was a blind analysis and results were not revealed until the very end after all signals were submitted.

“The data were taken in 2018 with the two species of isobar nuclei, Ruthenium and Zirconium” says Wang. “A blind analysis scheme was put in place such that the nuclear species is unknown to the analysts. All analysis codes were frozen in advance and then executed. At end the nuclear species are revealed and only at that point we know which species has a bigger signal.”

The entire process took three years. Five independent groups participated in the blind analysis, including Wang, Jie Zhao, postdoctoral scientist of Purdue University, and graduate student Yicheng Feng. This study was part of a broader effort in the quest for symmetry breaking phenomena in heavy ion collisions, which began over ten years ago.

“We are a leading institution in this physics,” says Wang. “The challenge is to fight the large background in the measurements. The latest result was that there may be a symmetry violating signal at 95% confidence level in the gold-gold collision data accumulated before 2018. The 2018 isobar data with the two nuclear species, different from gold, are predicted to yield a stronger signal. However, it turned out to be not as strong as predicted.”

As with any science, an unexpected outcome doesn’t mean the pursuit has ended.  In fact it’s the opposite.  Now researchers are better equipped to discover the CME because they have ruled out certain aspects of the research.  They are now armed with new clues in terms of the strength of the symmetry breaking effect and where to better look for it. 


Faculty Source: Fuqiang Wang

Media source:

Writer: Cheryl Pierce

Last Updated: Sep 3, 2021 1:34 PM

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