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 $$U_X(1)$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:msub> <mml:mi>U</mml:mi> <mml:mi>X</mml:mi> </mml:msub> <mml:mrow> <mml:mo>(</mml:mo> <mml:mn>1</mml:mn> <mml:mo>)</mml:mo> </mml:mrow> </mml:mrow> </mml:math> 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 $$95\%$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mn>95</mml:mn> <mml:mo>%</mml:mo> </mml:mrow> </mml:math> 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 $$\mathcal {O}(10^{-4})$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mrow> <mml:mi>O</mml:mi> <mml:mo>(</mml:mo> <mml:msup> <mml:mn>10</mml:mn> <mml:mrow> <mml:mo>-</mml:mo> <mml:mn>4</mml:mn> </mml:mrow> </mml:msup> <mml:mo>)</mml:mo> </mml:mrow> </mml:math> , depending on $$m_X$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>m</mml:mi> <mml:mi>X</mml:mi> </mml:msub> </mml:math> .