  Delayed single- and few-electron emissions plague dual-phase time projection
chambers, limiting their potential to search for light-mass dark matter. This
paper examines the origins of these events in the XENON1T experiment.
Characterization of the intensity of delayed electron backgrounds shows that
the resulting emissions are correlated, in time and position, with high-energy
events and can effectively be vetoed. In this work we extend previous S2-only
analyses down to a single electron. From this analysis, after removing the
correlated backgrounds, we observe rates < 30 events/(electron*kg*day) in the
region of interest spanning 1 to 5 electrons. We derive 90% confidence upper
limits for dark matter-electron scattering, first direct limits on the electric
dipole, magnetic dipole, and anapole interactions, and bosonic dark matter
models, where we exclude new parameter space for dark photons and solar dark
photons.
