Scientists at CERN said they had trapped dozens of hydrogen “antimatter” atoms, a technical feat that boosts research into one of the great puzzles of particle physics.

Under a theory expounded in 1931 by the eccentric British physicist Paul Dirac, when energy transforms into matter, it produces a particle and its mirror image – called an anti-particle – which holds the opposite electrical charge.

When particles and anti-particles collide, they annihilate each other in a small flash of energy.

If everything were equal at the birth of the cosmos, matter and anti-matter would have existed in the same quantities. The observable Universe would have had no chance of coming into being, as these opposing particles would have wiped each other out.

In reality, though, matter came to be far more dominant, and antimatter is rare.

But understanding why there is this huge imbalance presents a daunting technical challenge.

Until now, experiments have produced anti-atoms, namely of hydrogen, but only in a free state. That means they instantly collide with ordinary matter and get annihilated, making it impossible to measure them or study their structure.

In a paper published on Wednesday by the British journal Nature, a team at the European Organisation for Nuclear Research in Geneva, explain a method of snaring these so-called antihydrogen atoms.