The Higgs boson is a hypothetical massive elementary particle that is predicted to exist by the Standard Model of particle physics. The Higgs boson plays a crucial role in the Higgs mechanism responsible for breaking the electroweak symmetry of the Standard Model . If shown to exist, it would help explain why other elementary particles have mass. It is the only elementary particle predicted by the Standard Model that has not yet been observed in particle physics experiments. In the popular media, the particle is sometimes referred to as the God particle. They're not claiming the discovery yet, but physicists at the CERN laboratory in Switzerland may have finally found the Higgs boson. Just as the rumors suggested, both teams report tantalizing signs that the Higgs is there and that it has a mass about 133 times that of the proton. But one team sees additional oddities, so the results are far from clear.
The Higgs boson is a hypothetical massive elementary particle that is predicted to exist by the Standard Model of particle physics. The Higgs boson plays a crucial role in the Higgs mechanism responsible for breaking the electroweak symmetry of the Standard Model . If shown to exist, it would help explain why other elementary particles have mass. It is the only elementary particle predicted by the Standard Model that has not yet been observed in particle physics experiments. In the popular media, the particle is sometimes referred to as the God particle. They're not claiming the discovery yet, but physicists at the CERN laboratory in Switzerland may have finally found the Higgs boson. Just as the rumors suggested, both teams report tantalizing signs that the Higgs is there and that it has a mass about 133 times that of the proton. But one team sees additional oddities, so the results are far from clear.
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As of December 2011, the Higgs boson has yet to be confirmed experimentally, despite large efforts invested in accelerator experiments at CERN and Fermilab.
The good news is that the two groups see consistent signals at roughly the same energy, reinforcing each other's results. They also see those signs via different decay channels, the combinations of detectable particles that result when the Higgs falls apart.
However, one team's data plots also show peaks and wiggles at other masses. In effect, that team sees too many signs of possible Higgses, at various masses, and that has some physicists worrying that even the cluster of hints that coincide may be a mirage created by statistical fluctuations.
The data come from two gargantuan particle detectors, called ATLAS and CMS, fed by the $5.5 billion LHC. The collider smashes protons together in the centers of the two detectors to try to blast massive new particles into existence. ATLAS and CMS search for signs of Higgses popping into existence and decaying less than a trillionth of a second later into telltale combinations of familiar particles as predicted by prevailing theory.
Expectations had been running high. After 2 years of operation, ATLAS and CMS should have enough data to see some evidence of the Higgs if it is there. At first blush, both teams appear to have fulfilled that expectation, reporting possible signs—too weak to claim discovery—of the Higgs decaying into more than one combination of particles.
However, ATLAS researchers also searched for the Higgs decaying into two particles called Z bosons, each of which then decayed into either an electron and an antielectron or a muon (a cousin of the electron) and an antimuon. They see three candidate Higgs decays at 125 GeV with no other events in the vicinity. Taken together, the two types of decay neatly suggest that the Higgs might be there at 126 GeV; the chances that statistical noise could produce both signs are 1%.
At first glance, CMS appears to see something quite similar. CMS experimenters have looked for the Higgs decaying in the same two ways as their ATLAS counterparts, and into three other combinations that provide less mass resolution. CMS researchers see peaks in all five decay channels, and that's strong evidence that they're on to something, says Guido Tonelli of the University of Pisa in Italy, spokesperson for the CMS experiment. Taken altogether, the five decay combinations show a signal around 124 GeV, basically in agreement with ATLAS's signal, and the chances that background could cause such a signal are about 1 in 35.
But a closer look at CMS's mass plots for the individual channels reveals extra humps that give some physicists pause.
So the mystery of the Higgs boson still holds for the moment. It may be a lost particle hidden in the background noise. Or it may be smirking within the noise.
A Standard Model Higgs boson would confirm a theory first put forward in the 1960s, but there are other possible forms the Higgs boson could take, linked to theories that go beyond the Standard Model. A Standard Model Higgs could still point the way to new physics, through subtleties in its behavior that would only emerge after studying a large number of Higgs particle decays. A non-Standard Model Higgs, currently beyond the reach of the current experiments with data so far recorded, would immediately open the door to new physics, whereas the absence of a Standard Model Higgs would point strongly to new physics within the scope of the present study design.
For further information: http://news.sciencemag.org/sciencenow/2011/12/in-search-for-higgs-boson-physic.html?rss=1 or http://press.web.cern.ch/press/PressReleases/Releases2011/PR25.11E.html
Photo: http://en.wikipedia.org/wiki/File:CMS_Higgs-event.jpg
