On October 31, 2019, graduate student Christian Weber successfully defended his thesis, “New Search for H→ZZd→4l using pp collision data at √s=13 TeV with the ATLAS detector” (advisor O. Keith Baker).
Weber explained, “We are now in a peculiar era of particle physics. In 2012, we discovered the Higgs boson, which explains why particles have mass and completed the standard model. That means we now have a consistent explanation for the dynamics of matter on the smallest scales. However, we also know that this picture is incomplete in several ways. One of them is, for example, that it does not include dark matter, of which there is six times as much as regular matter in the universe. Now there are scientists all over the world that look for dark matter possible related particles in various ways and my work can be viewed in that ‘tradition’. Specifically, I am studying the Higgs boson with the goal to infer something meaningful about new, speculative particles that might stand in relation to dark matter. The idea here is that the Higgs boson is unique in the way it coupled to particles. Instead of coupling to any kind of charge, like all the other particles that we know, it couples to mass. So if there are any new particles that appear ‘dark’ as the lack any kind of charge, we might be able to detect them as long as they have mass. This research is only possible via the large collaborative efforts that stand behind the LHC and the ATLAS experiment, and a good example of Wright Lab’s mission to explore the invisible universe.”
In November, Weber will continue this research as a Research Associate in Physics in the ATLAS group at Brookhaven National Laboratory. He will also build toward the future of the ATLAS experiment and US particle physics by partaking in the preparations for the Snowmass 2021 meeting, which will advise on physics research policy within the US.
Thesis abstract: In 2012 the ATLAS and CMS experiments both reported the discovery of a new particle in the remnants of high-energy proton-proton collisions. The particles properties were consistent with the ones of the Standard Model Higgs boson. Its discovery, 58 years after its postulation, marked the completion of the Standard Model of Particle Physics.
Subsequent data taking at both experiments continued to record Higgs boson decays. With this increased dataset, we are now able to probe for new physics by studying the Higgs boson itself in ever greater detail. Specifically, the unique properties of the Higgs boson, it being chargeless, having sping-0, and coupling to mass, allow us now to probe previously inaccessible sectors of particle physics. That is, potential new particles whose interaction with Standard Model particles is otherwise forbidden or suppressed by lack of standard model charge or other symmetry considerations.
In this presentation I will detail the search for a beyond Standard Model gauge boson, that is not directly charged under the standard model. Specifically, the search for ‘dark’ Z-boson via the exotic Higgs boson decay H→ZZd→4l. I will give an overview of the machinery used to produce Higgs boson as well as the detector used to measure its decay products, the LHC and the ATLAS detector. In addition to that I will present limits on the cross section H→ZZd→4l and detail the statistical methods used in inferring the cross section limits from the recorded data.
Photos from the event: