The phenomenon of the Higgs boson interactions dramatically influences our understanding of particle physics, especially concerning the mass generation of elementary particles. As one of the central objectives of the ATLAS Higgs physics program, researchers aim to refine their measurements of the Higgs boson’s interactions with various elementary fermions and bosons. Such measurements are not merely for theoretical satisfaction; they provide critical insights into processes governed by the electroweak symmetry breaking.
The Higgs boson, discovered in 2012, acts as a cornerstone in the Standard Model of particle physics, primarily initiating the mass mechanism for other fundamental particles. According to electroweak theory, the interactions of the Higgs boson with fermions (like quarks and leptons) and bosons (like W and Z bosons) effectively produce mass. Consequently, the precision in measuring these interactions becomes paramount in either supporting or challenging existing theoretical frameworks.
During the recent International Conference on High-Energy Physics (ICHEP 2024), the ATLAS collaboration unveiled their latest findings, which showcase efforts to narrow down the measurement uncertainties associated with these interactions, focusing specifically on the three heaviest quarks: top, bottom, and charm. By reanalyzing datasets from the Large Hadron Collider (LHC) collected during Run 2 (2015-2018), the research team honed their analytical methodologies, leveraging enhanced jet tagging techniques essential for identifying decay products.
To grasp the significance of the latest findings, it’s pivotal to understand the role of jet tagging in collider physics. Jets emerge when unstable particles like quarks fragment post-decay, producing tightly packed sprays of hadrons detectable by sophisticated particle detectors. Identifying which quark flavor gives rise to a specific jet is central to determining the characteristics of events involving Higgs bosons.
By employing novel flavors of jet tagging that specifically cater to bottom and charm quarks, the ATLAS team dramatically improved their analyses’ sensitivity. Their innovations resulted in enhanced detection rates of Higgs decays, notably H → bb (Higgs to bottom quark pair) and H → cc (Higgs to charm quark pair). They reported a 15% increase in sensitivity to the former and a remarkably high threefold increase for the latter, providing unprecedented resolution into the Higgs boson’s decay pathways.
The ATLAS collaboration’s recent findings marked pivotal advancements in measuring Higgs production processes. Notably, they achieved their first observation of the WH, H → bb decay process with a statistical significance of 5.3σ and the ZH, H → bb decay with 4.9σ significance. These results not only enrich our understanding of Higgs interactions but also align closely with predictions offered by the Standard Model.
Interestingly, the decay of the Higgs boson into charm quarks remains extremely rare, with ATLAS establishing a limit on the rate of the VH, H → cc process, estimating it to be 11.3 times higher than Standard Model predictions. This underlines the challenges faced when probing lighter quark flavors and cements the necessity for further refined measurement techniques.
Future Prospects and Enhancing Precision
In advancing Higgs boson physics, the current measurements of Higgs interactions with the top quark reveal significant progress. Researchers concentrated on production processes that involve two top quarks, subsequently decaying into a bottom quark pair. Despite the complexity, which is exacerbated by substantial background noise from competing processes, updates to analysis strategies have doubled sensitivity to this critical interaction channel.
With the initiation of LHC Run 3 and the eventual prospects of the High-Luminosity LHC (HL-LHC), the prospect for detecting rare Higgs decay modes like H → cc appears considerably brighter. The ongoing commitment to refining analysis methods will likely yield deeper insights into the nature of Higgs boson interactions.
The latest strides made by the ATLAS collaboration reflect a blend of innovative approaches and comprehensive analysis, pushing the boundaries of what we understand about the Higgs boson. The pursuit of a more profound understanding of Higgs interactions holds implications that extend far beyond particle physics, potentially reshaping our grasp of the universe at its most fundamental level.