  In this paper, we consider the possibility that a new stage of matter,
stemming from hidden/dark sectors beyond the Standard Model, to be formed in
$pp$ collisions at the LHC, can significantly modify the correlations among
final-state particles. In particular, two-particle azimuthal correlations are
studied by means of a Fourier series sensitive to the near-side ridge effect
while assuming that hidden/dark particles decay on top of the conventional
parton shower. Then, new (fractional) harmonic terms should be included in the
Fourier analysis of the azimuthal anisotropies, encoding the hypothetical new
physics contribution enabling its detection in a complementary way to other
signatures.
