The study of fundamental particles has captivated physicists for decades, with one of the most significant milestones being the discovery of the Higgs boson at CERN’s Large Hadron Collider (LHC) in 2012. As part of an ongoing effort to deepen our understanding of the universe’s building blocks, the ATLAS collaboration is focused on measuring the interactions of the Higgs boson with elementary particles, particularly fermions and bosons. This article explores the implications of recent findings presented at the International Conference on High-Energy Physics (ICHEP) 2024, particularly concerning the interaction strengths between the Higgs boson and the heaviest quarks: top, bottom, and charm.
At the heart of particle physics lies the theory of electroweak symmetry breaking, which posits that the Higgs boson is pivotal in conferring mass to elementary particles through its interactions. When the Higgs boson interacts with quarks, such as the top, bottom, and charm quarks, it produces significant insights into the fundamental nature of mass. By studying how the Higgs boson is produced and how it decays into other particles, researchers can quantify these interaction strengths, enhancing our grasp of particle physics in the process.
The recent ATLAS results, derived from a reanalysis of data from the LHC’s Run 2 (2015-2018), underscore the collaboration’s quest for precision measurement in Higgs physics. Employing advanced analysis techniques, including refined jet tagging methods, researchers were able to draw conclusions about Higgs interactions that were not previously feasible. Understanding jet formation during Higgs boson decay provides a pathway to identifying the types of quarks involved—an essential factor for accurate measurement.
One of the significant advancements made during this research involves the process of jet tagging. When a Higgs boson decays into quarks, each quark creates a “jet,” a concentrated spray of particles that can be tracked and analyzed. ATLAS’s new tagging methods are specifically tailored to distinguish between charm and bottom quarks, which are crucial for the accurate assessment of Higgs decays into these states.
The results speak volumes about the improvement in sensitivity for the decay processes H→bb and H→cc. These improvements—15% for bottom quarks and a staggering threefold for charm quarks—illustrate how technological advancements in jet identification techniques can bolster detection capabilities in particle physics.
The culmination of these analysis methodologies was the 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 metrics represent some of the most precise measurements achieved in this domain. Despite this progress, challenges remain. The decay of the Higgs boson into charm quarks is considerably less frequent, exhibiting a suppression factor of 20 compared to that of bottom quarks. As a result, ATLAS established an upper limit on the rate of the VH, H→cc process, indicating room for further investigation.
Simultaneously, ATLAS researchers concentrated on interactions involving the top quark. Given the complexity and high background noise associated with the ttH, H→bb process, this endeavor posed significant challenges. Nonetheless, advancements in understanding the dominant background processes led to a twofold sensitivity improvement, allowing for a signal strength measurement that aligns with Standard Model predictions.
As the ATLAS collaboration anticipates the continued unfolding of the LHC Run 3 data and the subsequent High-Luminosity LHC (HL-LHC) phase, there is a palpable excitement in the scientific community regarding the potential for breakthroughs in Higgs physics. The prospect of detecting the elusive H→cc decay is becoming increasingly viable, promising to fill existing gaps in our understanding of particle interactions.
The journey of exploring Higgs boson interactions is not merely an academic pursuit but a significant step toward unraveling the universe’s deepest secrets. With remarkable advancements in analysis techniques and a commitment to precision, the ATLAS collaboration is at the forefront of this exciting field, pushing the boundaries of what we know about the fundamental forces that shape our reality. The implications of these studies resonate far beyond the confines of particle physics, contributing to broader inquiries into the nature of mass, matter, and the structure of the universe itself.