Probing the Chern-Simons Portal at the HL-LHC through Displaced Vertices from W Boson Associated Production

Abstract

This study explores the Chern-Simons portal model, an extension of the Standard Model that introduces a massive neutral vector boson $X$ associated with a $U_X(1)$ gauge symmetry. Motivated by gauge anomaly cancellation, the model incorporates heavy chiral fermions that induce observable effects through topological Chern-Simons interactions, despite being inaccessible at Large Hadron Collider energies. We investigate the associated production of the $X$ boson with a $W$ boson and jets at the High-Luminosity LHC with a center-of-mass energy of 14 TeV, considering different $X$ masses benchmarks. A multivariate analysis using Boosted Decision Trees is employed to separate signal from background processes. Detector effects are modeled using a fast simulation tuned to the HL-LHC environment, including realistic pile-up conditions with an average of 200 interactions per bunch crossing. We derive expected $95\%$ confidence level exclusion limits in two-dimensional parameter spaces involving the $X$ boson couplings. Our results demonstrate that the HL-LHC can achieve high sensitivity to gauge-anomaly-induced interactions, setting robust constraints on the $X$ boson coupling to the $W$ boson down to $\mathcal{O}(10^{-4})$, depending on $m_X$.