  We examine the stau-neutralino coannihilation (CA) mechanism of the early
universe. We use the minimal supergravity (mSUGRA) model and show that from
measurements at the Large Hadron Collider one can predict the dark matter relic
density with an uncertainty of 6% with 30 fb-1 of data, which is comparable to
the direct measurement by Wilkinson Microwave Anisotropy Probe. This is done by
measuring four mSUGRA parameters m0, m1/2, A0 and tan(beta) without requiring
direct measurements of the top squark and bottom squark masses. We also provide
precision measurements of the gaugino, squark, and lighter stau masses in this
CA region without assuming gaugino universality.
