God particle - basis for the Big Bang theory.

* Higgs boson is missing link of Standard Model of particle physics
* Boson posited to give energy and mass to other particles
* Results are not yet conclusive proof that particle exists

GENEVA, Dec 13 (Reuters) - International scientists said on Tuesday they had found signs of the Higgs boson, an elementary sub-atomic particle believed to have played a vital role in the creation of the universe after the Big Bang.

Peter Higgs, the 82-year-old British theoretical physicist who first proposed the existence of the particle in 1964 as the missing link of a grand theory of matter and energy, was watching the announcement on a webcast with colleagues at Edinburgh University, where he is an emeritus professor.

"I won't be going home to open a bottle of whisky to drown my sorrows, but on the other hand I won't be going home to open a bottle of champagne either," his colleague Alan Walker quoted him as saying after the announcement.

The leaders of two experiments, Atlas and CMS, revealed their findings to a packed seminar at the CERN physics research centre near Geneva, where they have tried to find traces of the elusive boson by smashing particles together at near light-speed in the Large Hadron Collider.

The experiments generated such excitement by independently reaching very similar conclusions. But the scientists were quick to warn that their results have not yet reached the level of certainty that would let them claim a discovery -- hence Higgs's caution.

Under what is known as the Standard Model of Physics, the boson is posited to have been the agent that gave mass and energy to matter after the creation of the universe 13.7 billion years ago - leading some to nickname it the "God particle".

Its discovery would fill the last remaining hole in the model. However, that does not mean it must exist, and some eminent physicists such as Stephen Hawking believe it does not.

"If the Higgs observation is confirmed ... this really will be one of the discoveries of the century," said Themis Bowcock, professor of particle physics at Britain's Liverpool University.

"Physicists will have uncovered a keystone in the makeup of the universe ... whose influence we see and feel every day of our lives."

BIG BANG CONDITIONS
The Large Hadron Collider at CERN, a vast underground particle accelerator that costs 200,000 Swiss francs ($215,000) an hour to run, is designed to recreate the conditions of the Big Bang to allow particles such as the Higgs boson to be found and studied.

While the boson's discovery would cement current knowledge about particles such as electrons and photons, proof that it does not exist would undermine the foundations of accepted theories of the make-up of the universe.

The particle is so short-lived that it can only be detected from the particles that it decays into. In the course of millions of collisions, the scientists are hunting for a significant excess of a particular combination of decay particles.

Although they are now converging on a particular profile for the Higgs, they will need another year's worth of such collisions to rule out a statistical fluke.

"The window for the Higgs mass gets smaller and smaller," said CERN Director General Rolf Heuer. "But please be prudent. Remember, we have not found it yet, nor have we excluded it yet. There is still Higgs hunting to be done."
Oliver Buchmueller, senior physicist on the CMS experiment, said: "It can still happen that it is a fluctuation, but all we see from both experiments is compatible with what we would expect for a Higgs signal to build up...

"But we really need the data from next year to be sure of what we're seeing."

Claire Shepherd-Themistocleus, head of the CMS Group at the STFC Rutherford Appleton Laboratory, said: "We are homing in on the Higgs ...

"We have had hints today of what its mass might be and the excitement of scientists is palpable. Whether this is ultimately confirmed or we finally rule out a low-mass Higgs boson, we are on the verge of a major change in our understanding of the fundamental nature of matter."