Why is the Higgs boson so important?

It has been called "the brick that built the universe", "the angel of creation" and "the god particle".

It is thought to have emerged from the Big Bang 13.7 billion years ago and have brought much of the rest of the flying debris together to form galaxies, stars and planets.

It is a key component of the "Standard Model" - the all-encompassing theory developed by physicists of how the cosmos as we know it works at its basic level of particles and forces.

But until now, in the four decades since it was first posited, no one has convincingly claimed to have glimpsed the Higgs Boson, let alone proved that it actually exists.

At an eagerly awaited briefing on Tuesday at the CERN research centre near Geneva, two independent teams of "Higgs Hunters" - a term they themselves hate - were widely expected to suggest they were fairly confident they had spotted it.

But not confident enough, in the physics world of ultra-precision where certainty has to be measured at nothing less than 100 percent, to announce "a discovery".

In the jargon, this level is described as 5 sigma, which would exclude the possibility that the results recorded by the ATLAS and CMS teams at CERN - the 21-nation European Organisation for Nuclear Research - are a fluke.

A million apples

As one scientist explained, that level of accuracy would equate to the 17th-century discoverer of gravity, Isaac Newton, sitting under his apple tree and a million apples one after another falling on his head without one missing.

Some leading scientists, including Briton Stephen Hawking, doubt that the tiny piece of matter that would be visible only as a trace on a computer screen is out there at all.

But most scientists involved in sifting through vast amounts of data produced in multi-trillions of particle impacts in CERN's Large Hadron Collider (LHC) over the past 20 months seem sure that it is, in one form or another.

As is another Briton, physicist Peter Higgs, who conceived the idea of the boson - a type of particle that carries force - in the mid-1960s to explain why much of the matter produced by the Big Bang has mass, and can therefore coalesce.

"I find it difficult to imagine how the theory (the Standard Model) works without it," he told the London monthly Prospect.

Higgs, now 82 and seen as a Nobel prize contender, conceived of a mechanism that would fit into the Standard Model and allow particles to have mass - which the model had previously failed to explain.

The mechanism, he argued, was a medium - since called the Higgs Field - existing throughout the universe, which gave other particles mass as they passed through it and were brought together by the Higgs boson.

Without this mechanism, a briefing paper by CERN explains, "the universe would be a very different place.... no ordinary matter as we know it, no chemistry, no biology, and no people".

Higgs - who, like the vast majority of particle physicists as shown in surveys, rejects any religious explanation of the origins of life and the cosmos - has no time for the more spiritual epithets applied to his boson.

"For me, it is there because it is there," he once told journalists on a visit to Geneva, where in the 1960s he worked for a while at CERN, adding archly: "As long as we can prove scientifically that it is."

(Editing by Louise Ireland)