Search for a Time-Dependent Z' Resonance in the Dimuon Channel

Abstract

We present a time-domain search strategy for resonances with periodically varying masses in high-energy collider data. Conventional resonance searches rely on time-integrated event samples and are therefore insensitive to signals whose properties evolve during data taking. To address this limitation, we develop a two-dimensional unbinned likelihood framework in invariant mass and time, allowing the reconstruction of signals that trace nontrivial trajectories in the $(m,t)$ plane rather than appearing as stationary resonances. As a benchmark scenario, we consider a $Z'$ boson arising from a gauged $U(1)_{B-L}$ extension of the Standard Model and introduce a phenomenological model in which the mediator mass undergoes periodic temporal modulation. The resulting signal manifests as a resonance whose position changes with time, producing distinctive patterns that are inaccessible to conventional analyses based solely on invariant-mass information. The method is implemented using dimuon events from the CMS Open Data corresponding to the Run~G data-taking period at $\sqrt{s}=13~\mathrm{TeV}$, with an integrated luminosity of $7.54~\mathrm{fb}^{-1}$. We derive upper limits on the gauge coupling $g'$ as a function of the $Z'$ mass for several choices of the modulation amplitude. The results demonstrate that incorporating temporal information can enhance sensitivity relative to standard time-integrated searches, particularly in regions with sufficient signal statistics.