  We develop a technique to directly study spinons (emergent spin S = 1/2
particles) in quantum spin models in any number of dimensions. The size of a
spinon wave packet and of a bound pair (a triplon) are defined in terms of
wave-function overlaps that can be evaluated by quantum Monte Carlo
simulations. We show that the same information is contained in the spin-spin
correlation function as well. We illustrate the method in one dimension. We
confirm that spinons are well defined particles (have exponentially localized
wave packet) in a valence-bond-solid state, are marginally defined (with
power-law shaped wave packet) in the standard Heisenberg critical state, and
are not well defined in an ordered N\'eel state (achieved in one dimension
using long-range interactions).
