The atom Photo: VCG

Chinese scientists have for the first time directly observed the Migdal effect in neutron-nucleus collisions in an experiment, confirming a quantum-mechanical prediction made 87 years ago of Migdal effect and providing crucial experimental evidence for the search for lighter dark matter particles in the universe, Science and Technology Daily reported on Thursday.

The related research findings were published on Wednesday in the journal Nature.

The Migdal effect was proposed in 1939 by Soviet theoretical physicist Arkady Migdal. It describes a quantum phenomenon in which, when a particle strikes an atomic nucleus, there is a small probability that the atom will emit a high-energy electron. This process can convert otherwise extremely faint signals into detectable electrical signals, offering a possible pathway for detecting light dark matter.
 
Zheng Yangheng, corresponding scientist of the study and a professor at the University of the Chinese Academy of Sciences, said the study overcomes a long-standing threshold bottleneck in light dark matter detection. He noted that future international dark matter experiments could use the Migdal effect to improve signal discrimination and extend the detectable mass range of dark matter, per report.
 
According to Science and Technology Daily, Zheng further explained that the Migdal effect has long been regarded as a key theoretical route for breaking through the energy-threshold limits of light dark matter searches. "However, for more than 80 years, the Migdal effect in neutral-particle collisions had never been directly confirmed experimentally," he said. "This left dark matter experiments relying on the effect facing persistent doubts due to the lack of experimental validation."
 
To achieve the breakthrough, the team developed a specialized gaseous pixel detector designed for high-precision imaging of nuclear recoil (NR) and Migdal electron tracks, and exposed it to neutrons produced by a compact D-D neutron generator, with the detector filled with a mixture of 40 percent helium and 60 percent dimethyl ether, according to Nature.
 
The authors noted that confirming the Migdal effect requires "the simultaneous observation of both the recoil nucleus and the Migdal electron, with the two tracks forming a topological structure with a common vertex." 
 
After collecting data for about 150 hours, the team identified six recoil nucleus-electron common-vertex events that met all selection criteria. "The observed signals have a statistical significance exceeding five standard deviations," the study reports, strongly indicating that the detected event topology originates from the Migdal effect rather than background processes.
 
Based on these observations, the researchers measured the ratio of the Migdal cross-section to the nuclear recoil cross-section, a result that is "in good agreement with the theoretical prediction within the experimental uncertainties."
 
Future work can build on these results to refine detection strategies and potentially enhance the sensitivity of dark matter searches, per article.
 
Global Times