August 28, 2018

The pixel detector used in this discovery that was built by Aaron Dominguez and his team.
The pixel detector used in this discovery that was built by Aaron Dominguez and his team. Photo credit: S. Hasegawa

Scientists now know the fate of the vast majority of all Higgs bosons produced in CERN

In late August at CERN (the European Organization for Nuclear Research), the Large Hadron Collider (LHC) experiments ATLAS and CMS jointly announced the discovery of the Higgs boson transforming into bottom quarks as it decays. This is predicted to be the most common way for Higgs bosons to decay, yet was a difficult signal to isolate because it closely mimics ordinary background processes. This new discovery is a big step forward in the quest to understand how the Higgs enables fundamental particles to acquire mass.

A Higgs boson is an elementary particle; a particle that is not made up of other particles, but which interacts with the other elementary particles. It is this interaction with the Higgs bosons’ associated field that creates the masses of the other elementary particles.

After several years of refining their techniques and gradually incorporating more data, both experiments at CERN have finally seen  evidence of the Higgs decaying to bottom quarks that exceeds the threshold of statistical significance typically required to claim a discovery. Both teams found their results were consistent with predictions based on the Standard Model.

This most recent discovery were made possible thanks to the work of Aaron Dominguez, dean of Catholic University’s School of Arts and Sciences, and his team working on the CMS pixel detector. That device acts like a super-fast digital camera which takes pictures of the radiation coming from the explosions that occur when proton beams collide 40 million times a second. This data was then used to find the most prevalent decay of the Higgs boson, which is difficult to spot because it mimics many ordinary background processes.

“Being able to identify and isolate bottom quarks in the experimental data is a huge challenge and required precise detector calibration and sophisticated b-quark tagging,” said Giacinto Piacquadio, a physicist at Stony Brook University who co-leads the Higgs-to-bottom-quarks analysis group. “We were only able to do these analyses thanks to years of work that came before.”

Higgs bosons are only produced in roughly one out of a billion LHC collisions and live only one-septillionth of a second before their energy is converted into a cascade of other particles. Because it’s impossible to see Higgs bosons directly, scientists use these secondary particles to study the Higgs’ properties. Since its discovery in 2012, scientists have been able to identify only about 30 percent of all the predicted Higgs boson decays. According to Viviana Cavaliere, a physicist at the U.S. Department of Energy’s Brookhaven National Laboratory, finding the Higgs boson decaying into bottom quarks has been priority number one for the last several years because of its huge favorability.

“Theory predicts that 60 percent of Higgs bosons decay into bottom quarks,” said Cavaliere, who is using this process to search for new physics. “Finding and understanding this channel is critical because it opens up the possibility for us to examine the behavior of the Higgs, such as whether it could interact with new, undiscovered particles.”

“I am thankful for having been able to contribute to this discovery and for being part of this large team of scientists from around the world working peacefully together on understanding the fundamental building blocks of creation,” said Dominguez.  When asked the impact of this result he continued, “By making this measurement of the interaction of the Higgs boson with bottom quarks, we have opened up a new window to see if it could also be interacting with new undiscovered particles, which would change our view of the universe.”

The next step is to increase the precision of these measurements so that scientists can study this decay mode with a much greater resolution and explore what secrets the Higgs boson might be hiding. Dominguez’s research group is currently working on research and development for this third-generation pixel detector to do just that. That detector will be built (in part) at Catholic University.