Scientists at the European Organization for Nuclear Research (better known by its French acronym CERN) announced on Wednesday that they have observed a new subatomic particle consistent with a Higgs boson. However, it is not yet clear what kind of Higgs boson has been found.
The experimental results have a significance level of five-sigma, meaning they are regarded as discoveries. (A one-sigma result could simply be a random fluctuation in the data while a three-sigma result counts as an observation.)
The Higgs boson was postulated as a means of providing mass to other subatomic particles, but until now it has not been detected experimentally. It cannot be detected directly, but must be identified indirectly, from detecting the predicted combinations of different particles it decays into.
CERN operates the giant Large Hadron Collider (LHC) particle accelerator located about 100 m underground on the Franco-Swiss border. Scientists from two of the LHC experiments, the Compact Muon Solenoid (CMS) and Atlas, made presentations at a seminar at CERN which was webcast live.
The first presentation was made by CMS scientist and spokesperson Joe Incandela, professor of physics at the University of California Santa Barbara, who stressed that the CMS collaboration involved 3 300 scientists around the world.
“We have observed a new boson at 125.3±0.6 GeV,” he announced. (GeV means giga-electron volt; although this is a measure of energy, because of Einstein’s famous equation E=mc2, where E stands for energy, m for mass and c for the speed of light in a vacuum, GeVs are used to express the mass of elementary particles.)
The second presentation was by Dr Fabiola Gianotti, senior research physicist at CERN and spokesperson for the Atlas experiment. She highlighted that the data from Atlas was processed at 80 sites around the world, often by young researchers.
The Atlas results established, with a confidence level of 95%, that the Higgs could not be in the mass ranges of 110 GeV to 122.6 GeV and 129.7 GeV to 558 GeV. “The best-fit [Higgs] signal strengths, normalised to the Standard Model expectations, for all studied [decay] channels [was] at mass equalling 126.5 GeV,” she stated.
“It was a global effort, it is a global effort, it is a global success,” enthused CERN director general Professor Rolf Heuer.