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A new subatomic particle discovered at the world's most powerful particle accelerator is indeed a much sought-after Higgs boson, scientists confirmed Thursday.
"To me it is clear that we are dealing with a Higgs boson, though we still have a long way to go to know what kind of Higgs boson it is," said Joe Incandela, spokesperson for CMS, in a statement. CMS is one of the two experimental efforts at the Large Hadron Collider near the French-Swiss border that have been hunting for the elusive particle.
The statement accompanied the release of the latest results from both CMS and ATLAS, the LHC's other Higgs boson-hunting experiment, at the Moriond physics conference in the Italy.
According to the Standard Model of Physics, the prevailing theory explaining the physical laws of nature, the Higgs boson imparts mass to other particles. The Higgs boson, nicknamed "the God particle" is the only particle in the Standard Model of Physics that had never been observed.
However, Higgs bosons also exist in some other models of physics that have been proposed, and it is not yet possible to rule out one of the lightest Higgs bosons that exist in a theory called supersymmetry, said Richard Teuscher, the deputy spokesperson for the Canadian scientists involved in ATLAS. Supersymmetry allows for the existence of multiple Higgs bosons, while the Standard Model allows for only one.
The results released Thursday by CERN, the European Organization for Nuclear Research that runs the LHC, include an analysis of all the data collected by CMS and ATLAS in 2012.
Back in July, CERN announced that researchers had found a Higgs-like particle with the right mass to be a Higgs boson, but stopped short of saying they had discovered a Higgs boson.
At that time, Teuscher said in an interview from CERN, researchers had collected only 65 per cent of the 2012 data. With the data gathered during the rest of the year, they were able to reduce the margin of error in the signals and measure not only the mass of the particle, but some other characteristics that are key to identifying it.
For example, researchers have been able to measure a property called spin, and based on that, they have just about ruled out the possibility that the particle they're seeing is something called a graviton, said Teuscher, an associate professor of physics at the University of Toronto and a research scientist with the Canadian Institute of Particle Physics.
"It's a beginning. And it so far looks like a Standard Model Higgs," he said. "But there's still many properties that we just don't have the data [for] yet. And there might still be surprises in the future."
The researchers are hoping to get that better data when the LHC is back up and upgraded to run at a higher energy in 2015, following a two-year shut-down that started late last year. In the meantime, they are continuing to analyze data that was already collected and are upgrading their particle detectors.
The ATLAS and CMS experiments hunt for the Higgs boson by smashing larger particles together at high speeds so that they break apart into smaller particles. Some of those particles decay into even smaller particles. Detectors look for signals left by the particles, and reconstruct what happened in a way that is similar to the way police reconstruct a vehicle collision based on the evidence at the scene. The two experiments use different techniques and detectors to home in on different kinds of signals.
Initially, with just a small amount of data, the signals had a large margin of error, giving a somewhat "blurry" picture of what the researchers may have found. However, the error decreases and the signals come into sharper focus as more and more data is gathered.