CERN scientists reporting at conferences in the UK and Geneva, Switzerland, 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.
Both teams claimed they had seen a “bump” in their data corresponding to a particle weighing in at about 125-126 gigaelectronvolts (GeV) – about 130 times heavier than the proton at the heart of every atom.
The results announced at CERN, home of the LHC in Geneva, were each met with thunderous applause.
Prof. Peter Higgs, the former University of Edinburgh theoretician who with five others predicted the Higgs particle’s existence in 1964, praised the LHC teams, calling the results “a testament to the expertise of the researchers”.
“I never expected this to happen in my lifetime and shall be asking my family to put some champagne in the fridge,” he said.
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.
Fabiola Gianotti, spokeswoman for the ATLAS experiment, announced even more irrefutable results.
“We observe in our data clear signs of a new particle, at the level of five sigma, in the mass region around 126 GeV,” she said.
Anticipation had been high and rumors 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 GeV.
Hints of the particle, revealed to the world by teams at the LHC in December 2011, have since strengthened markedly.
The $10 billion 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.
Prof. Stefan Soldner-Rembold, from the University of Manchester, said 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.
The Standard Model is the simplest set of ingredients – elementary particles – needed to make up the world we see in the heavens and in the laboratory
• Quarks combine together to make, for example, the proton and neutron – which make up the nuclei of atoms today – though more exotic combinations were around in the Universe’s early days
• Leptons come in charged and uncharged versions; electrons – the most familiar charged lepton – together with quarks make up all the matter we can see; the uncharged leptons are neutrinos, which rarely interact with matter
• The “force carriers” are particles whose movements are observed as familiar forces such as those behind electricity and light (electromagnetism) and radioactive decay (the weak nuclear force)
• The Higgs boson came about because although the Standard Model holds together neatly, nothing requires the particles to have mass; for a fuller theory, the Higgs – or something else – must fill in that gap