  The identity of Dark Matter (DM) is one of the most captivating topics in
particle physics today. The R-parity conserving Minimal Supersymmetric Standard
Model (MSSM), which naturally provides a DM candidate in the form of the
lightest neutralino ($\tilde{\chi}_{1}^{0}$), is used as a benchmark scenario
to show that a measurement of $\Omega_{\tilde{\chi}_{1}^{0}}h^{2}$ can be
achieved from measurements at the CERN Large Hadron Collider. Focus is placed
on compressed mass spectra regions, where the mass difference between the
$\tilde{\chi}_{1}^{0}$ and the $\tilde{\tau}_{1}$ is small and where the
$\tilde{\tau}_{1}$-$\tilde{\chi}_{1}^{0}$ coannihilation (CA) mechanism of the
early Universe plays an important role. The technique for measuring
$\Omega_{\tilde{\chi}_{1}^{0}}h^{2}$ relies on two proposed searches for
compressed Supersymmetry (SUSY): 1) production via Vector Boson Fusion (VBF)
processes; and 2) production with associated energetic jets from initial state
radiation (ISR). These approaches allow for the determination of the relic
abundance at the LHC for any model where CA is an important DM reduction
mechanism in the early Universe. Thus, it is possible to confirm that the DM we
observe today were $\tilde{\chi}_{1}^{0}$'s created in the early Universe. We
show that from measurements in the VBF and ISR SUSY searches at the LHC, the
dark matter relic density can be measured with an uncertainty of 25\% with 3000
fb$^{-1}$ of 13 TeV proton-proton data.
