  The interpretation of data obtained from particle image/tracking velocimetry
in the study of superfluid flows has been so far a challenging task. Tracking
particles (as solid hydrogen or deuterium) are attracted to the cores of
quantized vortices, so that their dynamics can be strongly affected by the
surrounding vortex tangle. Previous phenomenological arguments indicate that
tracking particles and micro-sized vortex rings could form bound states
(denoted here as VRP states). While a comprehensive description of the vortex
ring-particle bonding mechanism has to deal with somewhat involved flow
configurations, we introduce a simplified two-dimensional model of VRP states,
which captures essential qualitative features of their three-dimensional
counterparts. Besides an account of known experimental and numerical
observations, the model proves to be of great heuristic interest. In
particular, it sheds light on the important role played by viscous dissipation
(due to the normal component of the fluid), the Magnus force, and
topologically-excited vortex rings in the stability and dynamics of VRP states.
