The ATLAS collaboration at CERN is undertaking a pivotal journey in particle physics aimed at enhancing our comprehension of the Higgs boson and its interactions with fundamental particles. An essential aspect of this endeavor is the accurate measurement of how the Higgs boson interacts with various elementary particles – fermions and bosons alike. The interactions of the Higgs boson are central to the electroweak symmetry breaking theory, which significantly explains how mass is conferred to particles. In this exploration, recent findings shared during the International Conference on High-Energy Physics (ICHEP) 2024 have brought forth notable advancements in this discipline, particularly concerning the heaviest quarks: top, bottom, and charm.
At the heart of the Higgs boson framework is the principle that it is responsible for imparting mass to particles through its interactions. This signifies that measuring these interaction strengths is not merely about gathering data; it’s about revealing the very fabric of the physical laws that govern our universe. Improved techniques for analyzing data from the Large Hadron Collider (LHC) have unveiled significant breakthroughs. The recent re-evaluation of data from the LHC’s Run 2, which spanned from 2015 to 2018, has involved state-of-the-art analysis processes. These processes include sophisticated jet tagging methods, which are essential for mapping the Higgs boson’s decay pathways.
Jet tagging stands as a crucial procedure in particle physics, enabling researchers to identify the originating quarks of particle jets formed when the Higgs boson decays. Upon decaying into quark pairs, these quarks produce jets—narrow streams of particles observable by detectors. However, differentiating among various quark types involves understanding intricate properties of the jets. The introduction of bespoke tagging techniques specifically designed for bottom and charm quarks has significantly elevated the sensitivity of analyses related to Higgs boson decays. This has translated into a remarkable increase in the ability to identify Higgs decay channels: concerning the decay into bottom quarks (H→bb) and into charm quarks (H→cc), sensitivity improved by 15% and a factor of three respectively.
The results emerging from these refined methodologies are compelling. The ATLAS team achieved a groundbreaking observation of the WH, H→bb process, clocking in at a significance of 5.3σ, while ZH, H→bb was found with a significance of 4.9σ. These measurements represent the most precise investigations conducted thus far and align with predictions made by the Standard Model of particle physics. It’s noteworthy that decays into charm quarks remain elusive; their rarity is attributed to a suppression factor relative to bottom quark decays. Consequently, ATLAS has placed an upper limit on charm-related Higgs interactions, adding another layer of insight into these complex phenomena.
An additional highlight from the latest analysis is centered on the interaction of the Higgs boson with the top quark. This investigation revolved around the Higgs production in the presence of two top quarks and its decay into bottom quarks—a process characterized by intricate final states and significant background noise. With enhanced techniques to disentangle these complex interactions, the sensitivity of measuring this process was doubled compared to earlier experiments, yielding a signal strength of 0.81 ± 0.21 relative to Standard Model predictions. The promise that lies in upcoming data from Run 3, coupled with projected advancements in analysis techniques, bodes well for future explorations.
The anticipation surrounding these findings is palpable, especially as we gaze into the future with the High-Luminosity LHC (HL-LHC) on the horizon. As researchers inch closer to detecting elusive processes such as H→cc, the quest for deeper knowledge regarding the Higgs boson’s interactions aims not just for refinement but for redefining our understanding of the governing forces of nature. Each measurement propels us forward, illuminating previously shadowed pathways in the realm of particle physics and potentially leading to breakthroughs that could reshape our comprehension of the fundamental constituents of the universe. The collaboration’s continuous improvements and sustained pursuit of precision underscore the importance of these measurements in the broader framework of physics as we know it.