The Higgs boson, a fundamental particle theorized in the framework of the Standard Model of particle physics, stands as a cornerstone in our understanding of mass generation for elementary particles. It plays a pivotal role in the mechanism of electroweak symmetry breaking, which postulates that particles acquire mass through their interactions with the Higgs field. As research into the Higgs continues to evolve, experiments like those conducted by the ATLAS collaboration at the Large Hadron Collider (LHC) are crucial for measuring these interactions with unprecedented precision. A recent presentation at the International Conference on High-Energy Physics (ICHEP) 2024 highlights significant strides in understanding the Higgs boson’s coupling to the heaviest quarks—top, bottom, and charm.
In particle collisions, particularly those involving the Higgs boson, quarks emerge from the decay process, resulting in what physicists call jets. Jets are essentially collimated sprays of particles that arise as a consequence of quark fragmentation, predominantly manifesting as hadrons. Understanding the nature of these jets is fundamental for deciphering the types of quarks generated during a collision. This brings us to the concept of jet tagging, which is a technique employed to identify the “flavor” of the quark that produced a specific jet. Advanced tagging methods are essential for increasing the sensitivity of analyses that measure Higgs boson interactions, enabling researchers to distinguish between the different types of quarks involved in decays.
The ATLAS collaboration’s recent endeavors to refine their analysis techniques have yielded significant advancements in the sensitivity of their measurements. By reanalyzing data from LHC Run 2 (2015-2018) with improved jet tagging methods, researchers have successfully enhanced their ability to measure the strength of Higgs interactions with the top, bottom, and charm quarks. Particularly noteworthy are the developments in identifying jets produced by bottom and charm quarks. With these bespoke tagging techniques, the team increased their sensitivity to Higgs decays into bottom quarks (H→bb) and charm quarks (H→cc) by 15% and three times, respectively. Such improvements represent a meaningful leap forward in the precision of Higgs boson measurements at the LHC.
Significant Discoveries in Higgs Production Processes
Among the remarkable findings presented by the ATLAS collaboration is the first observation of Higgs boson production associated with a W boson, subsequently decaying into bottom quarks, achieving a significance of 5.3 sigma. Furthermore, the collaboration reported a significance of 4.9 sigma for the associated production of a Higgs boson with a Z boson, also decaying into bottom quarks. These results constitute some of the most accurate examinations of Higgs interactions to date. However, the decay of the Higgs boson into charm quarks remains elusive due to its suppressed occurrence—predicted to be twenty times less likely than its decay into bottom quarks. As a result, the ATLAS collaboration has set an upper limit on the Higgs decay into charm quarks associated with vector bosons.
Another pivotal aspect of the ATLAS presentation was the measurement of the Higgs boson’s interaction with the top quark. This analysis involved studying the production of Higgs in conjunction with top quarks (ttH) and its subsequent decay into a pair of bottom quarks. The complexity inherent in this process, compounded by substantial background noise, demands exceptional analytical skills. The ATLAS collaboration’s refined understanding of dominant background processes allowed them to bolster their sensitivity to this challenging measurement, demonstrating a signal strength for ttH, H→bb production at 0.81 ± 0.21 against Standard Model expectations.
The Path Forward: Future Prospects with HL-LHC
As the ongoing exploration of Higgs physics continues to unveil deeper layers of understanding, the High-Luminosity LHC (HL-LHC) sets the stage for even more refined measurements. Improved analysis techniques and an influx of new data promise to enhance our capability to probe the elusive H→cc process, which remains critical to establishing a comprehensive picture of Higgs boson interactions. The excitement surrounding these advancements underscores the importance of these exploratory efforts in shaping the future of particle physics and refining our understanding of the universe.
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