Title: Measurement of Relic Density at the LHC 

Abstract: 
Recent cosmological observations? have introduced tremendous
constraint on supersymmetry models. The minimal supergravity
(mSUGRA) model explains the observed dark matter content of the
universe and requires stau-neutralino co-annihilation mechanism in
the early universe for a large region of supersymmetry parameter
space. This co-annihilation region is characterized by a small mass
difference (~5-15 GeV) between the lightest stau and the lightest
neutralino. An accurate measurement of the small mass difference at
a collider is crucial to confirm the co-annihilation mechanism.
We  show that from measurements at the LHC it is possible to confirm 
this mechanism and using these measurements one can predict the dark 
matter relic density with an uncertainty of 6% with 30 fb-1 of data. 
This is possible by introducing measurements involving b-quark jets 
to determine the SUGRA parameters A0 and tan(beta) without direct 
measurements of the stop and sbottom masses. We measure all the mSUGRA 
parameters with high accuracy and our methods provide precision mass 
measurements of the gauginos, squark, and lighter stau without the 
mSUGRA assumption.

This talk is based on the following papers: arXiv:0802.2968;
Phys.Lett.B649:73-82,2007, Phys.Lett.B639:46-53,2006.