  The analysis of angular particle correlations can yield valuable insights
into the initial state of matter in high-energy collisions, thereby potentially
revealing the existence of Beyond the Standard Model scenarios such as Hidden
Valley (HV). In this study, we focus on a QCD-like hidden sector with
relatively massive HV quarks ($\lesssim 100$~GeV) which might enlarge and
strengthen azimuthal correlations of final-state SM hadrons. In particular, we
study the formation and possible observation of \textit{ridge-like} structures
in the angular two-particle correlation function at future $e^+e^-$ colliders,
with a much cleaner environment than in hadron colliders, such as the LHC.
