Announced today (from the BBC):
LHC claims new particle discovery
Cern scientists reporting at conferences in the UK and Geneva claim the discovery of a new particle consistent with the Higgs boson.
The particle has been the subject of a 45-year hunt to explain how matter attains its mass.
Both of the two Higgs-hunting experiments at the Large Hadron Collider have reached a level of certainty worthy of a "discovery".
More work will be needed to be certain that what they see is a Higgs, however.
The CMS team claimed they had seen a "bump" in their data corresponding to a particle weighing in at 125.3 gigaelectronvolts (GeV) - about 133 times heavier than the proton at the heart of every atom.
The result announced at Cern, home of the LHC in Geneva, was met with applause.
The CMS team claimed that by combining two of its data sets, they had attained a confidence level just at the "five-sigma" point - about a one-in-3.5 million chance that the signal they see would appear if there were no Higgs particle.
However, a full combination of the CMS data brings that number just back to 4.9 sigma - a one-in-2 million chance.
Joe Incandela, spokesman for CMS, was unequivocal.
"The results are preliminary but the five-sigma signal at around 125 GeV we're seeing is dramatic. This is indeed a new particle," he told the Geneva meeting.
Atlas results were even more promising.
"We observe in our data clear signs of a new particle, at the level of five sigma, in the mass region around 126 GeV," said Fabiola Gianotti, spokeswoman for the Atlas experiment at the LHC.
Massive problem
Anticipation had been high and rumours were rife before the announcement.
Indications are strong, but it remains to be seen whether the particle the team reports is in fact the Higgs - those answers will certainly not come on Wednesday.
A confirmation would be one of the biggest scientific discoveries of the century; the hunt for the Higgs has been compared by some physicists to the Apollo programme that reached the Moon in the 1960s.
Two different experiment teams at the LHC observe a signal in the same part of the "search region" for the Higgs - at a rough mass of 125 Gigaelectronvolts (GeV).
Hints of the particle, revealed to the world by teams at the LHC in December 2011, have since strengthened markedly.
The $10bn LHC is the most powerful particle accelerator ever built: it smashes two beams of protons together at close to the speed of light with the aim of revealing new phenomena in the wreckage of the collisions.
The Atlas and CMS experiments, which were designed to hunt for the Higgs at the LHC, each detect a signal with a statistical certainty of more than 4.5 sigma.
Five sigma is the generally accepted benchmark for claiming the discovery of a new particle. It equates to a one in 3.5 million chance that there is no Higgs and the "bump" in the data is down to some statistical fluctuation.
Statistics of a 'discovery'
- Particle physics has an accepted definition for a discovery: a "five-sigma" (or five standard-deviation) level of certainty
- The number of sigmas measures how unlikely it is to get a certain experimental result as a matter of chance rather than due to a real effect
- Similarly, tossing a coin and getting a number of heads in a row may just be chance, rather than a sign of a "loaded" coin
- A "three-sigma" level represents about the same likelihood as tossing eight heads in a row
- Five sigma, on the other hand, would correspond to tossing more than 20 in a row
- Independent confirmation by other experiments turns five-sigma findings into accepted discoveries
Prof Stefan Soldner-Rembold, from the University of Manchester, told BBC News earlier this week: "The evidence is piling up... everything points in the direction that the Higgs is there."
The Higgs is the cornerstone of the Standard Model - the most successful theory to explain the workings of the Universe.
But most researchers now regard the Standard Model as a stepping stone to some other, more complete theory, which can explain phenomena such as dark matter and dark energy.
Once the new particle is confirmed, scientists will have to figure out whether the particle they see is the version of the Higgs predicted by the Standard Model or something more exotic.
Scientists will look at how the Higgs decays or - transforms - into other, more stable particles after being produced in collisions at the LHC.
"We'll look at how often it decays into a pair of photons, how often it decays into Z bosons, how often it decays into W bosons," said Dr Tara Shears, from the University of Liverpool.
"It could match what the Standard Model predicts, but if there are deviations, that means there is new physics at work. That would be the first glimpse through the window at what lies beyond our current understanding."