Detection of SUSY in the stau-neutralino coannihilation region at the LHC

We study the feasibility of detecting the stau neutralino (τ˜1-χ˜10) coannihilation region at the LHC using tau (τ) leptons. The signal is characterized by multiple low energy τ leptons from χ˜20→ττ˜1→ττχ˜10 decays, where the τ˜1 and χ˜10 mass difference (ΔM) is constrained to be 5-15 GeV by current experimental bounds including the bound on the amount of neutralino cold dark matter. Within the framework of minimal supergravity models, we show that if hadronically decaying τ's can be identified with 50% efficiency for visible pT>20GeV the observation of such signals is possible in the final state of two τ leptons plus large missing energy and two jets. With a gluino mass of 830 GeV the signal can be observed with as few as 3-10fb−1 of data (depending on the size of ΔM). Using a mass measurement of the τ pairs with 10fb−1 we can determine ΔM with a statistical uncertainty of 12% for ΔM=10GeV and an additional systematic uncertainty of 14% if the gluino mass has an uncertainty of 5%.