Muons can be ‘seen’ – here the Moon's cosmic ray shadow, as seen in secondary muons detected 700m below ground, at the Soudan II detector

Its existence was predicted over 50 years ago - muonium is a theoretical atom that has yet to be created, detected or observed. True muonium is made of a muon and a counterpart anti-muon. These particles are commonplace in nature and are found when energetic particles from space strike the Earth’s atmosphere. However, muons and anti-muons have a momentary existence – their combination, true muonium, decays naturally into other particles in a few trillionths of a second. This makes observation of muonium extraordinarily difficult.

Theoreticians have delved into the world of experiment to try and design methods using particle accelerators to catch muonium before it decays. The first method they suggest has an electron and positron beam merging at a glancing angle to produce a muonium atom that would be thrown clear of any other particles in the accelerator. Ensuring the newly created muonium atoms are travelling very fast means that relativity slows the decay time making detection easier.

“We don’t usually work in this area, but one day we were idly talking about how experimentalists could create exotic states of matter,” said SLAC theorist Stanley Brodsky. “As out conversation progressed, we realised we just figured out how to make true muonium.”

Their second proposed method lets the electron and positron beams collide head on producing a muonium atom and photon mixed up in a cloud of particle debris. The muonium and photon would recoil against each other in the debris cloud and produce a unique signature that has not been previously looked for.

“It’s very likely that people have already created true muonium in this second way,” said Brodsky. “They just haven’t detected it yet.”

The group now hope that one of the world’s colliders will perform the experiments. After all – “who doesn’t want to see a new form of matter that no one’s even seen before?”

By Leila Sattary