New results from a joint ATLAS-CMS study at CERN’s Large Hadron Collider (LHC) provide intriguing hints that Higgs particles interact, a process that could reveal whether the Standard Model picture of the universe is complete.
Display of candidate double Higgs boson production events recorded by ATLAS (left) and CMS (right). Image credit: CERN.
The discovery of the Higgs boson at the LHC in 2012 marked the beginning of a new era in particle physics.
Since then, LHC researchers have investigated and measured how the Higgs boson interacts with other particles, a key mechanism by which these particles gain mass.
However, physicists have not yet observed the Higgs particle interacting with itself.
Understanding this process will not only test the limits of the Standard Model, currently the most valid theory in particle physics, but also help reveal whether the vacuum of the universe is stable.
The main challenge in studying Double Higgs production is that the process is incredibly rare.
The exact production rate has not yet been determined, but based on Standard Model predictions, physicists can expect that only one pair of Higgs particles will be produced for every approximately 1,500 single Higgs particles produced in an LHC collision.
To look for double Higgs production, the ATLAS and CMS teams look for signs of two Higgs particles decaying into other particles.
The physicists investigated a specific decay channel in which one side of the Higgs boson decays into a bottom quark and antiquark, and the other into a tau particle and its antiparticle. This is one of the best ways to study double Higgs production.
They had already explored double Higgs production using data from previous LHC runs.
Now, by combining these data with the latest third run of the LHC and introducing new machine learning techniques into their analysis, the researchers were able to more sensitively search for the double Higgs as the particle decays into two bottom quarks and two tau particles.
They identified more events than previously that appeared to be consistent with Double Higgs production, but still not enough events to observe the process.
However, they were able to set new constraints on the double Higgs production rate.
The ATLAS team sees 2.6 standard deviations above what would be expected without the Double Higgs formation.
In other words, the data suggests that pairs of Higgs bosons are being produced, even though the signal is not yet strong enough to be observed.
The CMS team ruled out a Double Higgs production rate that is more than four times the current prediction from the standard model.
Both collaborations also set limits on the Higgs self-coupling parameter, which determines how strongly a Higgs boson interacts with other Higgs bosons.
“These results are a promising sign for future analyzes combining the LHC’s complete Run 2 and Run 3 datasets and all decay modes, which could provide an interesting picture of the production of double Higgs bosons,” the scientists said.
“Looking further ahead, the high-luminosity LHC will be able to increase the number of collisions and record about six times as much data in experiments, bringing us even closer to observing double Higgs production.”
Source: www.sci.news
