"A search is reported for the pair production of a new quark b' with at least one b' decaying to a Z boson and a bottom quark. The data, corresponding to 2.0 fb(-1) of integrated luminosity, were collected from pp collisions at root s = 7 TeV with the ATLAS detector at the CERN Large Hadron Collider. Using events with a b-tagged jet and a Z boson reconstructed from opposite-charge electrons, the mass distribution of large transverse momentum b' candidates is tested for an enhancement. No evidence for a b' signal is detected in the observed mass distribution, resulting in the exclusion at a 95% confidence level of b' quarks with masses m(b)' < 400 GeV that decay entirely via b' -> Z + b. In the case of a vectorlike singlet b' mixing solely with the third standard model generation, masses m(b)' < 358 GeV are excluded."
Aad, G., Abbott, B., Abdallah, J., Khalek, S.a., Abdelalim, A.a., Abdesselam, A., et al. (2012). Search for Pair Production of a New b ' Quark that Decays into a Z Boson and a Bottom Quark with the ATLAS Detector. PHYSICAL REVIEW LETTERS, 109(7), 1-19 [10.1103/PhysRevLett.109.071801].