GENEVA (Reuters) - Tests have cleared the way for the start-up next month of an experiment to restage a mini-version underground of the "Big Bang" which created the universe 15 billion years ago, the project chief said on Monday.

Lyn Evans of the European Organisation for Nuclear Research (CERN) said weekend trials in the vast underground LHC machine in which the particle-smashing experiment will take place over the coming months and years "went without a hitch".

"We look forward to a resounding success when we make our first attempt to send a beam all the way round the LHC," said Evans, who heads the multinational team of scientists that shaped the project and the machine, the Large Hadron Collider.

The final tests involved pumping a single bunch of energy particles from the project's accelerator into the 27-km (17-mile) beam pipe of the collider and steering them counter- clockwise around it for about 3 kms (2 miles).

Earlier in the month a clockwise trial in the LHC -- which runs deep under French and Swiss territory between the Jura mountains and Lake Geneva -- had been equally successful, CERN said.

The LHC team now plans to send a full particle beam all the way around the collider pipe in one direction on September 10 as a prelude to sending beams in both directions and smashing them together later in the year.

That collision, in which both particle clusters will be traveling at the speed of light, will be monitored on computers at CERN and laboratories around the world by scientists looking for, among other things, a particle that made life possible.

The elusive particle, which has been dubbed the "Higgs boson" after Scottish physicist Peter Higgs who first postulated nearly 50 years ago that it must exist, is thought to be the mysterious factor that holds matter together.

Recreating a "Big Bang," which most scientists believe is the only explanation of an expanding universe, ought to show how stars and planets came together out of the primeval chaos that followed, the CERN team believes.

Efforts to track it down in a predecessor to the LHC at CERN, and in another experiment in the United States, failed. But scientists are confident that the vast leap in technologies represented by the LHC will make the difference.

Higgs, a 79-year-old Edinburgh University professor who as an atheist angrily rejects the idea of calling the boson the "God particle" -- believes it will show up very quickly once the beams are colliding in the LHC.

"If it doesn't," he said during a visit to CERN earlier this year, "I shall be very, very puzzled."