  We study the feasibility to observe sterile neutrinos with masses in the
range 5 GeV $< m_N < 20$ GeV at the LHC, using exclusive semileptonic modes
involving pions, $W\to \ell N \to \pi \ell\ell, 2\pi \ell\ell$ and $3\pi
\ell\ell$. We thus cover a mass window that is between what can be studied in
meson factories and high energy colliders. We run simulations for these
exclusive events, where pions should be distinguished from the background
provided the neutrino decay exhibits a vertex displacement from its production
point. In a previous work we have estimated the theoretical rates and here we
analyze the observability of the processes at the LHC, given the fact that
exclusive hadronic states may be difficult to identify.
  We study the sensitivity bounds for the observation and discovery of sterile
neutrinos in the above mass range. By the end of Run-3, current bounds on
heavy-to-light lepton mixings in the lower mass end ($\sim 5$ GeV) could be
improved by about an order of magnitude to $|U_{\ell N}|^2\sim 5\times
10^{-6}$, and the High-Luminosity LHC could reach $|U_{\ell N}|^2 \lesssim
3\times 10^{-7}$ in the mass range below 11 GeV. Studying in addition equal
sign and opposite sign dileptons, the Majorana or Dirac character of the
sterile neutrino could be revealed.
