2012-07-04 12:26:24
Scientists find new particle, probably the Higgs
By Chris Wickham and Rosalba O'Brien | Reuters
GENEVA/LONDON (Reuters) - Scientists at Europe's CERN research center have found a new subatomic particle that could be the Higgs boson, the basic building block of the universe.
"We have indeed discovered a particle consistent with the Higgs boson," John Womersley, head of a British public research body, told journalists and scientists in London on Wednesday.
"These results mark a significant breakthrough in our understanding of the fundamental laws that govern the universe."
Joe Incandela, spokesman for one of the two teams hunting for the Higgs particle told an audience at CERN near Geneva: "This is a preliminary result, but we think it's very strong and very solid."
CERN's director general Rolph Heuer said: "As a layman, I would say I think we have it."
Addressing the scientists assembled in the CERN auditorium, Heuer asked: "Would you agree?" They burst into applause.
Peter Higgs, the 83-year-old British physicist who proposed the existence of the Higgs boson in the 1960s, was at CERN to welcome the news. Clearly overwhelmed, his eyes brimming, he told the symposium: "It is an incredible thing that it has happened in my lifetime."
UNIVERSAL THEORY
The Higgs theory explains how particles clumped together to form stars, planets and life itself.
Without the Higgs particle, the particles that make up the universe would have remained like a soup, the theory goes.
It is the last undiscovered piece of the Standard Model that describes the fundamental make-up of the universe. The model is for physicists what the theory of evolution is for biologists.
What scientists do not yet know from the latest findings is whether the particle they have discovered is the Higgs boson as described by the Standard Model. It could also be a variant of the Higgs idea or an entirely new subatomic particle that could force a rethink on the fundamental structure of matter.
The last two possibilities are, in scientific terms, the most exciting.
Packed audiences of particle physicists, journalists, students and even politicians filled conference rooms in Geneva and London to hear the announcement.
Despite the excitement, physicists cautioned that there was still much to learn.
"We still much we don't know about particles - this is only the beginning of a new journey. We have closed one chapter and opened another," Peter Knight of Britain's Institute of Physics told Reuters.
Oliver Buchmueller, a senior physicist on one of the research teams, told Reuters: "If I were a betting man, I would bet that it is the Higgs.
"But we can't yet say that definitely yet. It is very much a smoking duck that walks and quacks like the Higgs. But we now have to open it up and look inside before we can say that it is indeed the Higgs."
Higgs called it a great achievement for the Large Hadron Collider, the 27-km (17-mile) long particle accelerator built in a tunnel underneath the French-Swiss border where experiments to search for the Higgs boson have taken place.
In a statement, he added: "I never expected this to happen in my lifetime and shall be asking my family to put some champagne in the fridge."
(Additional reporting by Robert Evans in Geneva; Editing by Janet Lawrence and Alastair Macdonald)
By Paul Rincon Science editor, BBC News website, Geneva
Cern scientists revealing results from the Large Hadron Collider have claimed 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 LHC on the Franco-Swiss border 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 the European Organization for Nuclear Research (Cern) were met with thunderous applause.
At the meeting, Prof Peter Higgs, the former University of Edinburgh theoretician who with five others predicted the Higgs particle's existence in 1964, praised the efforts of the LHC teams.
Start Quote
I think we have it - we have a discovery
Rolf Heuer Cern director-general
"It's really an incredible thing its happened in my lifetime," 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.
Massive problem
Anticipation had been high and rumours were rife before the announcement.
Peter Higgs Along with five other theoreticians, Peter Higgs predicted the particle in the 1960s
Indications are strong, but it remains to be seen whether the particle the team reports is in fact the simplest "standard model" Higgs, rather than something more complex - and those answers will certainly not come on Wednesday.
Cern director-general Rolf Heuer summed up the two presentations succinctly, saying: "I think we have it - we have a discovery. We have an observation consistent with a Higgs boson - but which one?"
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 $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'
Swiss franc coin
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.
Scientists will look at how the new particle decays -or transforms - into other, more stable particles after being produced in collisions at the LHC to figure out whether the particle they see is the version of the Higgs predicted by the Standard Model or something more exotic. .
"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."
The Standard Model and the Higgs boson
Standard model
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