New results from a joint ATLAS and CMS analysis at CERN’s Large Hadron Collider (LHC) provide intriguing evidence of possible double Higgs boson production—a rare process that could reveal whether the Standard Model of particle physics 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 opened a new era in particle physics.
Since then, researchers have studied how the Higgs boson interacts with other fundamental particles. These interactions are central to the mechanism through which elementary particles acquire mass.
However, scientists have not yet directly observed the Higgs boson interacting with itself. Measuring this process would provide an important test of the Higgs field and the Standard Model, the leading theory describing fundamental particles and their interactions.
Higgs boson self-interaction could also help physicists understand whether the vacuum of the Universe is stable.
The main challenge in detecting double Higgs boson production is its extreme rarity. Although the precise production rate has not yet been measured, Standard Model calculations suggest that only one pair of Higgs bosons is created for approximately every 1,500 individual Higgs bosons produced in LHC collisions.
To search for Higgs boson pairs, the ATLAS and CMS collaborations look for the characteristic products of two Higgs bosons decaying into other particles.
In this analysis, researchers examined a specific decay channel in which one Higgs boson decays into a bottom quark and an antiquark, while the other decays into a tau lepton and an ant tau lepton. This decay channel is among the most promising ways to investigate double Higgs production.
The collaborations had previously searched for Higgs boson pairs using data from earlier LHC runs. By combining those results with data from the LHC’s third run and applying advanced machine-learning techniques, the teams carried out a more sensitive search for events in which the two Higgs bosons ultimately produce two bottom quarks and two tau leptons.
The new analysis identified more candidate events than previous searches. However, the number of events was still insufficient to claim the first definitive observation of double Higgs boson production.
Nevertheless, the researchers established new limits on the rate at which Higgs boson pairs are produced.
The ATLAS collaboration reported an excess corresponding to 2.6 standard deviations above the background expected in the absence of double Higgs production. In other words, the data show a suggestive signal of Higgs boson pairs, but the evidence is not yet strong enough to confirm the process as an observation.
The CMS collaboration excluded a double Higgs production rate greater than approximately four times the current Standard Model prediction.
Both collaborations also established limits on the Higgs self-coupling parameter, which describes the strength of the interaction between Higgs bosons.
“These results are a promising sign for future analyses combining the LHC’s complete Run 2 and Run 3 datasets and all decay modes, which could provide an interesting picture of double Higgs boson production,” the scientists said.
“Looking further ahead, the High-Luminosity LHC will increase the number of collisions and allow experiments to collect approximately six times more data, bringing researchers closer to observing double Higgs boson production and measuring the Higgs self-coupling.”
Source: www.sci.news