  We show that in TeV-scale left-right (L-R) symmetric seesaw models, there are
new dominant contributions to the collider signals of heavy Majorana neutrinos
arising from the heavy-light neutrino mixing, which directly probe the seesaw
matrix in a certain class of models. We propose a way to distinguish this
contribution from the widely discussed one that only probes the Majorana nature
of the heavy right-handed neutrinos, by analyzing some simple kinematical
variables. We find that in this class of L-R seesaw models the existing LHC
data already yield slightly stronger constraints on the heavy-light neutrino
mixing than those derived for standard seesaw models, and the improvement will
be significant as more data are collected.
