  Based on large-scale quantum Monte Carlo simulations, we examine the
dynamical spin structure factor of the Balents-Fisher-Girvin kagome lattice
quantum spin-$1/2$ model, which is known to harbor an extended $Z_2$ quantum
spin liquid phase. We use a correlation-matrix sampling scheme combined with a
stochastic analytic continuation method to resolve the spectral functions of
this anisotropic quantum spin model with a three-site unit-cell. Based on this
approach, we monitor the spin dynamics throughout the phase diagram of this
model, from the XY-ferromagnetic region to the $Z_2$ quantum spin liquid
regime. In the latter phase, we identify a gapped two-spinon continuum in the
transverse scattering channel, which is faithfully modeled by an effective
spinon tight-binding model. Within the longitudinal channel, we identify gapped
vison excitations and exhibit indications for the translational symmetry
fractionalization of the visons via an enhanced spectral periodicity.
