A team of researchers led by Colorado School of Mines Postdoctoral Researcher Joseph Smolsky and Associate Professor of Physics Kyle Leach, alongside a significant undergraduate and graduate student team, has made advancements in understanding neutrinos — mysterious particles that are among the most abundant in the universe but poorly understood. Their findings will be published in the journal Nature’s Feb. 13 issue.
The research provides the first direct experimental constraints on the spatial extent, or “quantum size,” of a neutrino using a novel precision measurement technique. This approach differs from traditional particle physics experiments that depend on large, high-energy colliders. Instead, the team is part of the BeEST (pronounced “beast”) experiment, which utilizes “tabletop-scale” precision measurements of radioactive decay to gain insights into fundamental particles.
By embedding radioactive beryllium atoms into superconducting sensors thinner than a human hair, the researchers track the decay process with high accuracy. “Our work is a prime example of how small-scale, high-precision experiments can complement the discoveries made at large particle colliders,” said Leach. “By precisely measuring the behavior of lithium atoms produced in the decay of beryllium, we gain direct access to quantum properties of neutrinos—particles that are notoriously difficult to detect.”
Studying neutrinos presents challenges due to their rare interaction with other particles. The BeEST experiment addresses this by leveraging quantum entanglement. When a lithium nucleus and a neutrino are produced simultaneously in radioactive decay, precise measurements of the lithium nucleus allow researchers to infer otherwise inaccessible properties of the neutrino. With just one superconducting sensor measuring for 20 hours, the researchers improved upon all previous limits on neutrino spatial extent.
These results offer insights for theoretical models of neutrino behavior and may influence future studies of subatomic particles. “This is just the tip of the iceberg,” Leach said. “Our findings could have far-reaching implications, from refining the standard model of particle physics to improving methods for detecting neutrinos from nuclear reactors and astrophysical sources. We are excited for what comes next.”
The BeEST experiment is a collaborative effort involving Mines’ Physics Department and Quantum Engineering and Nuclear Engineering programs, with contributions from Lawrence Livermore National Laboratory, Pacific Northwest National Laboratory, TRIUMF (Canada), and various institutions across Europe. This work is supported by the U.S. Department of Energy and the Gordon and Betty Moore Foundation.
