  Particles with a sub-millimeter decay length appear in many models of physics
beyond the Standard Model. However, their longevity has been often ignored in
their LHC searches and they have been regarded as promptly-decaying particles.
In this letter, we show that, by requiring displaced vertices on top of the
event selection criteria used in the ordinary search strategies for
promptly-decaying particles, we can considerably extend the LHC reach for
particles with a decay length of $\gtrsim 100~\mu{\rm m}$. We discuss a way of
reconstructing sub-millimeter displaced vertices by exploiting the same
technique used for the primary vertex reconstruction on the assumption that the
metastable particles are always pair-produced and their decay products contain
high-$p_{\rm T}$ jets. We show that, by applying a cut based on displaced
vertices on top of standard kinematical cuts for the search of new particles,
the LHC reach can be significantly extended if the decay length is $\gtrsim
100~\mu{\rm m}$. In addition, we may measure the lifetime of the target
particle through the reconstruction of displaced vertices, which plays an
important role in understanding the new physics behind the metastable
particles.
