Spin Identification of the Mono-Z′ Resonance in Muon-Pair Production at the ILC with Simulated Electron–Positron Collisions at √s = 500 GeV

Abstract In this analysis, we examine the angular distribution of low-mass dimuon pairs produced in simulated electron–positron collisions at the proposed International Linear Collider (ILC), which operates at a center-of-mass energy of 500 GeV and has an integrated luminosity of 4 ab$^{-1}$. Our focus is on the $\cos\theta _{\text{CS}}$ variable, which is defined in the Collins–Soper frame. In the Standard Model, the production of low-mass dimuon pairs is primarily driven by the Drell–Yan process, which exhibits a notable forward–backward asymmetry. However, many scenarios beyond the Standard Model predict different shapes for the $\cos\theta _{\text{CS}}$ distribution. This angular distribution can be valuable for distinguishing between these models, especially in the event of observing excesses beyond the Standard Model expectations. We utilized the mono-Z$^{\prime }$ model to interpret the simulated data. In the absence of any discoveries of new physics, we establish upper limits at the 95% confidence level on the masses of various particles in the model, which includes the spin-1 $\mathrm{Z}^{\prime }$ boson and fermionic dark matter.