  The use of charged pileup tracks in a jet to predict the neutral pileup
component in that same jet could potentially lead to improved pileup removal
techniques, provided there is a strong local correlation between charged and
neutral pileup. In Monte Carlo simulation we find that the correlation is
however moderate, a feature that we attribute to characteristics of the
underlying non-perturbative dynamics. Consequently,
`neutral-proportional-to-charge' (NpC) pileup mitigation approaches do not
outperform existing, area-based, pileup removal methods. This finding contrasts
with the arguments made in favour of a new method, "jet cleansing", in part
based on the NpC approach. We identify the critical differences between the
performances of linear cleansing and trimmed NpC as being due to the former's
rejection of subjets that have no charged tracks from the leading vertex, a
procedure that we name "zeroing". Zeroing, an extreme version of the
"charged-track trimming" proposed by ATLAS, can be combined with a range of
pileup-mitigation methods, and appears to have both benefits and drawbacks. We
show how the latter can be straightforwardly alleviated. We also discuss the
limited potential for improvement that can be obtained by linear combinations
of the NpC and area-subtraction methods.
