The CMS Collaboration is presenting six new results at the 19th International Workshop on Top Quark Physics (TOP2026), held from October 5 to 9, 2026, in the Antalya Region of Türkiye.
The results cover precision cross section measurements, novel extractions of top quark properties, and studies of rare production modes observed for the first time. These results use data from both Run 2 and Run 3 of the LHC.
Among the highlights is a new determination of the coupling strength of a W boson to bottom and charm quarks. This coupling determines how often a bottom quark transforms into a charm quark through the weak interaction. The measurement analyzes events with top quark pairs recorded in 2024 and identifies the rare W decays with advanced jet flavor tagging algorithms. Thanks to these advances in machine-learning-based techniques, it is possible to determine this fundamental parameter using top quark decays. The result follows a measurement of the same coupling using Run 2 data presented earlier this year and provides an important complementary approach to measurements based on decays of B hadrons.
CMS also presents two new cross section measurements using Run 3 data, employing the data sample recorded in 2022 and 2023. One analysis measures the electroweak production of a single top quark, which can be used to infer information about the internal structure of the proton and the strength of the weak interaction involving the top quark. The second analysis measures the production of a top quark pair together with a W boson and compares the result with the most precise theoretical predictions currently available. Both results are the first measurements of these processes at the Run 3 center-of-mass energy.
Using the Run 2 data set, CMS is also performing precision cross section measurements of top quark pair production. One analysis studies extensively the orientation of the top quark spins, as well as the correlations between the spins of the top quark and antiquark. These measurements provide a detailed test of the Standard Model description of top quark production and reveal some differences between the data and theoretical predictions. Another result studies top quark pairs produced together with additional charm or bottom quarks, where in particular the identification of charm quark jets is experimentally challenging. For the first time, several observables relating to the charm quark jets are studied, providing an important test of the modelling of heavy flavour production.
Finally, CMS presents the first measurement of the rare production of a single top quark in association with both a W boson and a photon. The analysis uses a machine-learning technique to distinguish the signal from background processes. The measured rate agrees with the Standard Model prediction within uncertainties, and the signal is seen with strong statistical significance. The result opens a new experimental window on the electroweak interactions of the top quark.