Dark matter-motivated searches for exotic fourth-generation mirror quarks in Tevatron and early LHC data

We determine the prospects for finding dark matter at the Tevatron and LHC through the production of exotic fourth-generation mirror quarks T^' that decay through T^'→tX, where X is dark matter. The resulting signal of tt̄+E\;T has not previously been considered in searches for fourth-generation quarks, but there are both general and specific dark matter motivations for this signal, and with slight modifications, this analysis applies to any scenario where invisible particles are produced in association with top quarks. Current direct and indirect bounds on such exotic quarks restrict their masses to be between 300 and 600 GeV, and the dark matter's mass may be anywhere below m_T^'. We simulate the signal and main backgrounds with MadGraph/MadEvent-Pythia-PGS4. For the Tevatron, we find that an integrated luminosity of 20 fb^-1 will allow 3σ discovery up to m_T^'=400 GeV and 95% exclusion up to m_T^'=455 GeV. For the 10 TeV LHC with 300 pb^-1, the discovery and exclusion sensitivities rise to 490 GeV and 600 GeV. These scenarios are therefore among the most promising for dark matter at colliders. Perhaps most interestingly, we find that dark matter models that can explain results from the DAMA, CDMS, and CoGeNT collaborations can be tested with high statistical significance using data already collected at the Tevatron and have extraordinarily promising implications for early runs of the LHC.