  Liquid Argon Time Projection Chamber (LArTPC) detectors observe ionization
electrons to measure charged particle trajectories and energy. In a LArTPC, the
long time ($\sim$ms) between when the ionization is produced and when it is
collected means that diffusion can smear the charge by an amount comparable to
the spatial resolution of the detector, given by the spacing between charge
sensing channels ($\sim$mm). This smearing has an impact on the distribution of
energy losses measured by each channel. In particular, the smearing increases
the length of the charged particle trajectory observed by each channel, and
therefore the most-probable-value (MPV) of particle energy loss recorded by
that channel. We find, for example, that this effect shifts the MPV $dE/dx$ of
a muon with an energy of 1 GeV by ${\sim}4$% for a 2 ms drift time and 4.7 mm
wire spacing, as in the DUNE-FD LArTPC. This has implications for the
energy-scale calibration and electron lifetime measurements in a LArTPC, which
both use the MPV of the muon energy loss distribution as a "standard candle".
The impact of diffusion on these calibrations is assessed.
