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Higgs boson resurfaces in LHC data

The Higgs appeared in the second run of the LHC about twice as fast as it did in the first.

The Higgs boson is peeking out of the new data collected during the second run of the Large Hadron Collider, scientists reported today at the International Conference on High Energy Physics in Chicago.

The Higgs boson is a short-lived particle that transforms into a cascade of more stable particles immediately after it is produced. Because scientists cannot measure the Higgs directly, they look instead at the more stable particles it leaves behind.

In 2012, during the LHC’s first run, scientists discovered the Higgs boson based on its decay into three different types of particles: photons, W bosons and Z bosons. In the data from the second run, which began in 2015, scientists have reconfirmed its decay into photons and Z bosons.

The Standard Model predicts that the Higgs boson can transform into at least eight different pairs of particles. The most common transformation should be the Higgs transforming into bottom quarks; this has not yet been observed.

Particle collisions during the LHC’s second run have been 1.6 times more energetic than those produced during the first run. The higher-energy collisions produce Higgs bosons more than twice as fast. This rediscovery in the new data looked at around 1500 trillion collisions recorded during 2015 and 2016 and saw the Higgs re-emerge exactly where expected with unmistakable significance.

But finding the Higgs boson is only the beginning. Now that scientists have re-established its existence, they want to use the new data to study its properties more in depth.

“The particle itself is just one of the little elements,” says Ivan Pogrebnyak, a graduate student at Michigan State University who worked on the ATLAS two-photon rediscovery analyses. “The ultimate goal is to understand the laws of nature—not just discover a particle but measure its properties and how it fits inside the whole scheme.”

The Higgs boson helps explain the masses of certain elementary particles and is a cornerstone of the Standard Model of particle physics, the best model scientists have to explain the fundamental interactions of the subatomic universe.

In addition to measuring its predicted properties, physicists want to push beyond the Standard Model and see if the Higgs holds any clues to new physics.

“We can use the Higgs as a key to look beyond the Standard Model,” says Andrea Massironi, a postdoctoral researcher at Northeastern University who presented some of the CMS experiment’s latest Higgs results today at ICHEP. “We’ve only begun to study the Higgs, and don’t know what secrets it might hold.”