The hunt for the fabled "God particle" that lends mass to matter and holds the universe together could soon be over.
Scientists giving a progress report on the search today are expected to say they are almost at the point of confirming the existence of the Higgs boson.
Almost, but not quite. The process of proving the Higgs is real is a gradual one, similar to getting closer to a familiar face seen from afar.
In December last year scientists at the Large Hadron Collider (LHC) - the "Big Bang" particle accelerator which recreates conditions a billionth of a second after the birth of the universe - revealed they had caught a first tantalising glimpse of the Higgs.
Since then they have sifted through vast quantities of data from innumerable high energy collisions in an effort to reduce the odds of being wrong.
A statistical standard of proof known as "five sigma" would be the ultimate confirmation of a discovery. In this case, the chances of a mistake are one in a million.
Today, scientists are expected to announce a significant step further towards the five sigma goal.
Possibly, they might even be at "four sigma", a hair's-breadth away from having the Higgs in their grasp.
In that case the final "discovery" of the Higgs particle will be virtually a foregone conclusion.
At the Large Hadron Collider , scientists shoot two beams of protons - the "hearts" of atoms - at each other round 27 kilometres of circular tunnels at almost the speed of light.
When the protons smash together the enormous energies involved cause them to decay into an array of more fundamental particles. These may then decay further into yet more particles.
By following the decay patterns, scientists hope to see the "fingerprint" of the Higgs boson.
Physicists need the Higgs to plug a gaping hole in the "Standard Model", the theory that explains all the particles, forces and interactions making up the universe.
So far nothing has been observed to account for mass, and the fact that some particles weigh more than others.
According to the theory, the Higgs boson is the emissary of an all-pervading "Higgs field" that gives matter mass. The more particles interact with the field, the more massive they become and the heavier they are.
A Standard Model universe without the Higgs boson could not exist.
Everything would behave as light does, floating freely and not combining with anything else. There would be no atoms, made from conglomerations of protons, neutrons and electrons, no ordinary matter, and no us.
Finding no evidence of the Higgs would mean tearing up the Standard Model and going back to the drawing board with a completely new set of theories.
Professor Higgs, 83, who is retired from the University of Edinburgh, is fast becoming a global celebrity as creator of the theory behind the "God particle".
He dreamed up the concept in a moment of inspiration while walking in the Cairngorms in 1964.
Prof Higgs's groundbreaking proposal was that particles acquire mass by interacting with an all-pervading field spread throughout the universe. The more they interact, the more massive and heavy they become.
A "boson" particle was needed to carry and transmit the effect of the field - the Higgs boson.
Peter Higgs was born in Newcastle in 1929. He studied theoretical physics at King's College London.
In 2006, Prof Higgs retired from the University of Edinburgh, assuming the title of emeritus professor.
Prof Higgs is described by friends and colleagues as "very unassuming" and shy. Some believe his retiring nature might even have held back his career.
Now, despite his best efforts to keep a low profile, the spotlight is turning on him.
The Standard Model is a beautiful mathematical construction that seems to be a good reflection of reality. But it contains a gaping hole.
While nearly all the building blocks of the universe it predicts have been observed, one very important particle is missing. The Higgs boson, or rather the field associated with it, is said to be what gives matter mass and weight.
It is because of the Higgs, says the theory, that some particles weigh more than others.
Describing how the Higgs gives matter mass requires some imaginative analogy. The Higgs field has been described as a kind of all-pervading "cosmic treacle" spread throughout the universe.
Particles moving through the "treacle" stick to it , slow down, lose energy, and become heavier.
In particle physics, force-carrying particles are called "bosons". The Higgs boson acts as an emissary of the Higgs field, helping to transmit its mass-giving force.
Scientists have filled the hall at Cern where the announcement will be made shortly.
Auditorium filling up fast for #Higgs seminar, first in line were physicists from @princeton & @Cornell - they arrived at 10:45 last night!by CERN via twitter 7/4/2012 6:27:10 AM
The auditorium at CERN is packed - I understand loads couldn't get in. There's a quiet anticipation. #Higgsby BobEagle2 via twitter 7/4/2012 6:59:38 AM
