Human error's being blamed for the breakdown of the world's largest atom-smasher.
The European Organisation for Nuclear Research says it looks as though one of the 10 thousand connections in the 27km Large Hadron Collider overheated, and made a hole that leaked helium into the tunnel.
The head of the project, Lyn Evans says the atom-smasher won't be up and running before the end of April.
Buried underground in Geneva, the LHC took nearly 20 years to complete and at six billion Swiss francs ($A7.12 billion) is one of the costliest and most complex scientific experiments ever attempted.
It aims to resolve some of the greatest questions surrounding fundamental matter, such as how particles acquire mass and how they were forged in the Big Bang that created the universe 13 billion years ago.