The tWZ process and the couplings of the top quark

Since the start of the Large Hadron Collider (LHC) at 13 TeV, the CMS experiment recorded a proton- proton collisions data set amounting to 150/fb. The heaviest known elementary particle of the standard model, the top quark, has been observed again, and first measurements of its properties enter the precision regime. The standard model of particle physics has been confirmed and, so far, no physics beyond the standard model has been found. Therefore, we now test any theoretically viable potential deviation. That`s interesting, because many such tests are conducted for the first time. For the top quark, there are plenty of predictions for deviations in the electroweak couplings. Those lead to changes in the decay products that we can test in the experiment. Events with a top quark, a W boson, and a Z boson have peculiar properties. They depend sensitively on many hypothetical deviations, and we can learn the most from them. And that`s precisely the plan. Small deviations in the decay products` kinematic properties are used to tackle the big questions of particle physics. Is the standard model valid after all, or do we have to replace it with something new? Moreover, this "tWZ" process has not been observed and is a worthwhile target in its own right. In this way, the top quark allows us an in-depth view into the physics beyond the standard model.

Using data from the CMS Experiment from Runs II-III of the Large Hadron Collider at CERN, we measured the rates of the ttZ, tWZ, and WZ processes with high precision. To make this possible, we designed multilepton selections and robust data-driven controls that cleanly separated the signal from look-alike processes. Advanced machine-learning techniques-developed and validated by the team-provided the decisive discrimination while remaining transparent and reproducible. We interpreted the results within the Standard Model Effective Field Theory, setting new, complementary constraints on several top-quark couplings. The analysis produced reusable software and open documentation that other LHC groups and students are already using. Alongside the research, we trained early-career scientists in modern analysis methods, statistics, and open science, with several now leading related efforts in CMS. We shared the excitement with the public through talks, media features, and student exercises explaining how we find extremely rare signals in trillions of collisions. The project strengthened Austria's role in precision top-quark physics and showcased the value of sustained investment in accelerator science and computing. Most importantly, it delivered a new, incisive test of nature's fundamental laws and opened fresh pathways to search for physics beyond the Standard Model.