  We investigate non-standard interaction effects in antineutrino-electron
scattering experiments with baselines short enough to ignore standard
oscillation phenomena. The setup is free of ambiguities from the interference
between new physics and oscillation effects and is sensitive to both
semileptonic new physics at the source and purely leptonic new physics in the
weak interaction scattering at the detector. We draw on the TEXONO experiment
as the model system, extending its analysis of non-standard interaction effects
at the detector to include the generally allowed non-standard interaction phase
at the detector and both non-universal and flavor changing new physics at the
reactor source. We confirm that the current data allows for new physics
constraints at the detector of the same order as those currently published, but
we find that constraints on the source new physics are at least an order of
magnitude weaker. The new physics phase effects are at the 5% level, noticeable
in the 90% C.L. contour plots but not significantly affecting the conclusions.
Based on projected increase in sensitivity with an upgraded TEXONO experiment,
we estimate the improvement of sensitivity to both source and detector
non-standard interactions. We find that the bounds on source parameters improve
by an order of magnitude, but do not reach parameter space beyond current
limits. On the other hand, the detector new physics sensitivity would push
current limits by factors 5 to 10 smaller.
