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