Scientists have directly observed muonic molecules in resonance states for the first time, using a high-resolution X-ray detector, a new Science Advances study reports.

Resonance states are critical in determining the reaction rate of muon catalyzed fusion (µCF), a process that utilizes elementary particles known as muons. Within muonic molecules, the nuclei are confined in extremely close proximity, enabling nuclear fusion to occur even at room temperature without the need for plasma.

Currently, research aimed at the practical application of nuclear fusion is underway worldwide. In principle, fusion offers highly safe energy with no risk of runaway accidents. It utilizes fuel easily extracted from seawater and produces clean energy without carbon dioxide emissions.

When fundamental particles are heavier or lighter than expected, physicists’ understanding of the universe can tip into the unknown. A particle that is just beyond its predicted mass can unravel scientists’ assumptions about the forces that make up all of matter and space. But now, a new precision measurement has reset the balance and confirmed scientists’ theories, at least for one of the universe’s core building blocks.

In a paper appearing in the journal Nature, an international team including MIT physicists reports a new, ultraprecise measurement of the mass of the W boson.

The W boson is one of two elementary particles that embody the weak force, which is one of the four fundamental forces of nature. The weak force enables certain particles to change identities, such as from protons to neutrons and vice versa. This morphing is what drives radioactive decay, as well as nuclear fusion, which powers the sun.

Particle accelerators reveal the heart of nuclear matter by smashing together atoms at close to the speed of light. The high-energy collisions produce a shower of subatomic fragments that scientists can then study to reconstruct the core building blocks of matter.

An MIT-led team has now used the world’s most powerful particle accelerator to discover new properties of matter, through particles’ “near-misses.” The approach has turned the particle accelerator into a new kind of microscope—and led to the discovery of new behavior in the forces that hold matter together.

In a study appearing this week in the journal Physical Review Letters, the team reports results from the Large Hadron Collider (LHC)—a massive underground, ring-shaped accelerator in Geneva, Switzerland. Rather than focus on the accelerator’s particle collisions, the MIT team searched for instances when particles barely glanced by each other.