Measurement of the Invisible Width of the Z Boson Using Open Data from the CMS Experiment

This work presents a measurement of the invisible width of the \( Z \) boson, a fundamental parameter of the Standard Model, using CMS Open Data from proton-proton collisions at a center-of-mass energy of \( \sqrt{s} = 13\,\text{TeV} \), corresponding to an integrated luminosity of \( 16{,}290\,\text{fb}^{-1} \). The invisible width, associated with the decay \( Z \to \nu \bar{\nu} \), is inferred from the missing transverse momentum observed in \( Z + \text{jets} \) events. This measurement provides valuable insight into the coupling between the \( Z \) boson and neutrinos. The result is compared with previous measurements published by the CMS Collaboration. In addition, the study explores event selection techniques using machine learning, specifically employing Graph Neural Networks (GNNs) as an alternative to traditional cut-based methods. Furthermore, the research includes technical contributions to the upgrade of the CMS muon system, focusing on the assembly and testing of the Improved Resistive Plate Chambers (iRPCs). These gaseous detectors, designed for high-precision timing, will be installed in the detector’s endcap regions to extend pseudorapidity coverage and significantly enhance muon detection and tracking efficiency, especially in the high-luminosity environment anticipated in future LHC upgrades.