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Elusive Feature Of Higgs Boson Just Confirmed By Experiments At CERN


Robin Andrews

Science & Policy Writer


An artist's impression of the Higgs field, properly known as the Brout-Englert-Higgs field. Daniel Dominguez/CERN

Remember the Higgs boson? Well, thanks to an international effort to unlock more of its secrets, it’s back in the news. As announced by CERN, a brand-new property of the all-important particle has finally been observed, precisely as predicted, proving that particle physicists are nailing it at the moment.

In case you’ve forgotten, here is the briefest of summaries of what ol’ Higgsy is, and why understanding it matters. As explained by none other than CERN, our utmost understanding of the basic building blocks of the universe – fundamental particles – and how they interact and are governed by four fundamental forces is encapsulated in the Standard Model of particle physics.


There’s a lot going on in this ever-evolving model, but the key component for us at this present moment is the Higgs field: a hypothesized, omnipresent quantum field that gave these fundamental particles their mass.

The particle linked to this field is termed the Higgs boson – and is used in major particle physics experiments, including the ATLAS and CMS experiments at CERN’S Large Hadron Collider. As noted by Scientific American, the mass of the Higgs boson could be inferred by assessing the effect it would have on other particles and fields, and their properties.

Back on July 4, 2012, after a long series of experiments – and plenty of quadruple checking – it was announced at CERN that a new particle had been spotted. It came in at a mass of 125 billion electronvolts, consistent with what the Standard Model predicted for the Higgs boson.

Its official discovery didn’t mean the world of particle physics was done with poking it around, though. Experiments designed to probe its properties and behaviors have been near-continuously carried out over the past few years, and this latest suite has managed to uncover a key characteristic of the particle that has been long predicted but never observed.


These experiments looked at how the Higgs boson interacts with quarks, subatomic particles far tinier than atoms. There’s a variety of quarks – up, down, bottom, top, strange, and charm – with the “top” flavor being the heaviest. Its mass means that scientists expect it to interact with the Higgs most strongly, but the nature of this cooperative framework has been fairly elusive.

In order to uncover this, the team required a Higgs boson to be produced together with a top quark and its antimatter equivalent, a top anti-quark, a process known as ttH production. This wasn’t exactly easy: only 1 percent of Higgs bosons are made in this way. Even then, these quarks quickly annihilate each other and the Higgs boson turns into other particles within the merest of moments.

Thankfully, the CMS and ATLAS experiments managed it. Their data, which first started appearing in April, revealed that this particular interaction had been directly observed.

Now, in line with the LHCP conference in Bologna this week, CERN has confidently declared that “the findings of the two experiments are consistent with one another and with the Standard Model, and give us new clues for where to look for new physics.”


The CMS results have been published in Physical Review Letters, with the ATLAS experiment’s data up for publication soon, although they are already available to look through on arXiv.

Imperial College London physicist and lead researcher on the CMS experiments, Dr Thomas Strebler, said in a statement that “it’s very nice to look up for a moment and realize we have made a fundamental contribution to understanding the origin of mass.”


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