  A variety of new-physics models predict metastable particles whose decay
length is $\lesssim 1$ mm. Conventional displaced-vertex searches are less
sensitive to this sub-millimeter decay range, and thus such metastable
particles have been looked for only in usual prompt decay searches. In this
paper, we show that an additional event-selection cut based on the vertex
reconstruction using charged tracks considerably improves the sensitivity of
ordinary searches which rely only on kinematic selection criteria, for
particles with a decay length of $\gtrsim 100$ $\mu \text{m}$. To that end, we
consider a metastable gluino as an example, and study the impact of this new
event-selection cut on gluino searches at the LHC by simulating both the signal
and Standard Model background processes. Uncertainty of the displaced-vertex
reconstruction due to the limited resolution of track reconstruction is taken
into account. We also discuss possibilities for optimization of the kinematic
selection criteria, which takes advantage of significant reduction of
background through the requirement of displaced vertices. In addition, we
demonstrate that using the method discussed in this paper it is possible to
measure the lifetime of metastable particles with an ${\cal O}(1)$ accuracy at
the high-luminosity LHC. Implications for a future 100 TeV collider are also
studied, where produced particles tend to be more boosted and thus it is easier
to detect the longevity of metastable particles.
