  In this work, more than a dozen solar energetic particle (SEP) events are
identified where the source region is magnetically well-connected to at least
one spacecraft at 1~au. The observed intensity-time profiles, for all available
proton and electron energy channels, are compared to results computed using a
numerical 1D SEP transport model in order to derive the parallel mean free
paths (pMFPs) as a function of energy (or rigidity) at 1~au. These inversion
results are then compared to theoretical estimates of the pMFP, using observed
turbulence quantities with observationally-motivated variations as input. For
protons, a very good comparison between inversion and theoretical results is
obtained. It is shown that the observed inter-event variations in the inversion
pMFP values can be explained by natural variations in the background turbulence
values. For electrons, there is relatively good agreement with pMFPs derived
assuming the damping model of dynamical turbulence, although the theoretical
values are extremely sensitive to the details of the turbulence dissipation
range which themselves display a high level of variation.
