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

We study the feasibility of detecting the stau neutralino ((tau) over tilde (1)-(X) over tilde (0)(1)) coannihilation region at the LHC using tau (T) leptons. The signal is characterized by multiple low energy tau leptons from (X) over tilde (0)(2) -> tau(tau) over tilde (1) -> tau tau(X) over tilde (0)(1) decays, where the (tau) over tilde (1) and (X) over tilde (0)(1) mass difference (Delta M) 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 tau's can be identified with 50% efficiency for visible P-T > 20 GeV the observation of such signals is possible in the final state of two tau leptons plus large missing energy and two jets. With a gluino mass of 830 GeV the signal can be observed with as few as 3-10 fb(-1) of data (depending on the size of Delta M). Using a mass measurement of the tau pairs with 10 fb(-1) we can determine Delta M with a statistical uncertainty of 12% for Delta M = 10 GeV and an additional systematic uncertainty of 14% if the gluino mass has an uncertainty of 5%. (c) 2006 Elsevier B.V. All rights reserved.