Researchers at CERN have discovered the first evidence for the direct decay of the Higgs boson into fermions, a strong indication that the particle found two years ago is the Higgs boson.

The discovery confirms that the bosons decay to fermions - which is a group of particles that includes all quarks and leptons - as previously predicted by the Standard Model of particle physics, according to a CERN press release.

"This is an enormous breakthrough," said Markus Klute, an assistant professor of physics at Massachusetts Institute of Technology (MIT), according to the release. "Now we know that particles like electrons get their mass by coupling to the Higgs field, which is really exciting." 

Researchers from the ATLAS and Compact Muon Solenoid (CMS) conducted experiments at the European Organisation for Nuclear Research (CERN). They said that they observed a new particle in the mass region of 125 to 126 gigaelectronvolts (GeV). 

Studies showed that the new particle's properties were consistent with those predicted for the Higgs boson by the Standard Model. Before they were able to confirm the discovery, they had to conduct more research first.

The researchers wanted to determine if there was a single Higgs or a number of different Higgs particles, as previously predicted by a number of extensions of the Standard Model, according to the release.

"What we are trying to do is establish whether this particle is really consistent with the Higgs boson, the particle we predict in our Standard Model, and not one of many Higgs bosons, or an imposter that looks like it but has a different origin," Klute said. 

Previous experiments conducted at CERN's Large Hadron Collider, in Switzerland, showed that the new particles have no spin, and rapidly decay by splitting into pairs of Z bosons, W bosons, and photons, just like the Higgs boson of the Standard Model.

It remained unclear whether or not they could also decay into fermion pairs, according to Klute.

The team from the CMS Collaboration has demonstrated that the bosons also decay to fermions in a fashion that matches up with the Standard Model Higgs, according to the release.

"We have now established the main characteristics of this new particle, in its coupling to fermions and to bosons, and its spin-parity structure; all of these things are consistent with the Standard Model," Klute said. 

To figure out if the particles could decay to fermions, researchers fired protons at each other in a 6-meter-diameter solenoid and used specialized detectors to determine the particles that were produced in the collisions, according to the release.

Researchers were hunting for particles called tau leptons, which have a mass of around 1.7 GeV. This makes them around 3,500 times heavier than an electron. 

The researchers were able to confirm the presence of decay to tau leptons with a confidence level of 3.8 standard deviations, a one in 10,000 chance that the signal discovered would appear if there wasn't Higgs particles, according to the release.

Research was posted in the journal Nature Physics.

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