After an almost fifty year-long search, the Higgs boson’s discovery was finally announced in 2012. But even six years after the discovery of the elusive particle, many mysteries remain associated with the Higgs boson’s properties and our understanding of the way mass is generated, not only concerning the Higgs boson’s own mass - the theory predicts a mass for the Higgs boson that is in striking disagreement with the measured value -, but also how the other elementary particles obtain their mass due to the Higgs field or the Higgs (BEH) mechanism.
A new result could give new clues on these remaining mysteries and, at the same time, offer hints to new physics.
The ATLAS and CMS experiments at the Large Hadron Collider at CERN have observed the top quark, the most massive known elementary particle, discovered in 1995 at Fermilab in the US, directly interacting with the Higgs field.
This is a very important result ... one of the milestones in high-energy physics.Fabio Cerutti
The discovery was announced on Monday 4th of June at the Large Hadron Collider Physics (LHCP) 2018 conference in Bologna. Both the ATLAS and the CMS experiment had searched for this phenomenon and both found clear evidence that it occurs.
The presented results describe the observation of the so-called "ttH production" process, the associated production of the Higgs boson from two top quarks, a top and a top antiquark.
One of the most important features of the Higgs boson is how it couples to other particles because all elementary particles should obtain their mass due to the interaction with the Higgs field.
To study this interaction, the ATLAS and CMS researchers looked at how the Higgs boson decays, by measuring the probabilities of the Higgs boson decaying in different ways to other particles.
Since the decay into a top quark pair is not possible because even a single top quark is much heavier than the Higgs boson, they looked at the production of Higgs bosons from top quarks, for a Higgs boson and a top and top antiquark, found in a collision, so-called associated production of the Higgs boson with two top quarks, tth for short.
But measuring the ttH production process is difficult because it is rare: only 1% of all Higgs bosons are produced in association with two top quarks and, in addition, top quarks and Higgs bosons are never directly detected because they decay too rapidly and in many ways.
Using data from proton – proton collisions collected at energies of 7-13 TeV, the ATLAS and CMS teams performed several independent searches for ttH production, each targeting different Higgs-decay modes (to W bosons, Z bosons, photons, τ leptons, and bottom-quark jets). To maximize the sensitivity, each experiment then combined the results from all of its searches.
ATLAS physicists for example examined five years of collision data to achieve this result. “This was one of the most demanding searches ever carried out by the ATLAS Collaboration, requiring a concerted effort from several analysis teams,” said Fabio Cerutti, ATLAS Higgs working group convener.
The findings of the two experiments were found to be consistent with one another and with the standard model.
Together, these results are a great step forward in studying the properties of the Higgs boson and the origins of mass, and on the other hand, they could give clues for where to look for new physics.
Since the Higgs boson interacts most strongly with top quarks and because of the strength of this interaction, the results are an ideal laboratory to study the detailed nature of the origins of mass and have the potential to answer the remaining mysteries.
Yet undiscovered heavy particles referring to new physics could likewise participate in the studied process and alter the result. In this respect, the Higgs boson could also be seen as a portal to new physics.
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"The Mystery of the Higgs Boson"!