Or it might mean that something else is going on, for example an additional new particle involved in Higgs decays, making the Higgs decay more frequently into two photons. The errors are large so this could just be a fluke. "ATLAS found the frequency of excess photons produced to be twice that expected by the standard model Higgs. "The decay into two photons is the most egregious channel," says Allanach. another new particle in addition to the Higgs. And excitingly, the slightly unexpected results for one mode of decay, where the Higgs boson decays into two photons, might indicate something new. "Sometimes you need closer inspection to find out whether it's really your best friend, or actually your best friend's twin." And if it does turn out to be a sibling of the Higgs then we will need new physics to account for it.Īccording to Allanach, however, we can be sure we've found a Higgs boson-like particle. "It's a bit like spotting a familiar face from afar," said CERN Director General Rolf Heuer. Today's evidence shows that a new particle has indeed been discovered, but physicists won't rest easily until more analysis has confirmed it as the Higgs boson described by Higgs' theory or if it's a new exotic particle. The data from the ATLAS detector for decays into two photons also shows a peak at 125-126GeV, further proof of the presence of the new particle. This means that the chance that ordinary background processes that do not involve a Higgs fluctuate by the amount seen is only about one in 3.5 million. Today's evidence weighs in at the five sigma level for both the ATLAS and CMS experiments. Such indirect observations don't give us 100% certainty of course, so physicists quantify their certainty using sigma levels.
#HIGGS BOSON PLUS#
(See the Plus article Countdown to the Higgs for more detail.) And if the actual data looks different from the predicted background data in the right way (if it agrees with the predictions of the standard model plus the Higgs) then that counts as evidence that the Higgs does exist. Using the standard model, which doesn't include the Higgs boson, it is possible to predict what the data collected by the LHC should look like as a result of the behaviour of all the other particles in the standard model (referred to as the background in the presentation today). It is the properties and behaviour of the particles it decays into that can be detected by the ATLAS and CMS experiments at the LHC. Physicists could not hope, however, to see the Higgs boson directly, as it decays into other particles immediately. The bump at 125-126GeV indicates the presence of the new particle.
The data from the CMS detector for decays into two photons. Higgs said at the end of the seminar: "For me the really incredible thing is that it's happened in my lifetime." " And this has meant they have been able to discover the Higgs boson far quicker than anyone, including Peter Higgs himself, dreamed. We're operating beyond the design, beyond the expectations. As Fabiola Gianotti, the head of the ATLAS experiment, said: "It's a miracle. "It's a very exciting time." The data has come in far quicker than anyone expected. "We now have more than double the data we had last year," said CERN Director for Research and Computing, Sergio Bertolucci before the announcement. It could be something else but all this particle's properties are consistent with a standard model Higgs boson."īetween April and June 2012 the LHC delivered more data than during all of 2011, and it's the results from analysing this data that were presented to the seminar today, webcast around the world.
"They know it's a particle and they are just being really strict. "They know they've found something that hasn't been found before," says Ben Allanach, a theoretical particle physicist and one of the many people who has been a part of this long search. It has a mass of 125-126 GeV and all its properties are consistent with the Higgs boson predicted by the standard model of particle physics. (Image ATLAS)Īlthough they were being careful not to say definitively they had obseved the Higgs boson in the ATLAS and CMS experiments at the LHC, both teams announced they have indisputably discovered a new particle. An event recorded by the ATLAS detector in 2012 showing the characteristics expected from a Higgs boson decaying into four electrons.
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