Search for ttbar production in the all-hadronic channel in ATLAS with sqrt{s} = 7 TeV data

We present a search for ttbar production in the all-hadronic channel. The analysis is performed using 36 pb−1 of pp collisions produced at the LHC with a center-of-mass energy of sqrt{s} =7 TeV and recorded with the ATLAS detector. In this analysis the signal events are characterized by the presence of at least six jets, of which two are required to be identified as originating from a b-quark using a secondary vertex b-tagging algorithm. A data-driven method, based on the parametrization of the b-tagging rate determined in a control region, is used to model the QCD multijet background. A binned likelihood fit is performed to search for the signal where the background normalization is unconstrained. The fit is based on aχ^2 variable that uses the reconstructed masses of the top quark and W boson as constraints. The observed (expected) upper limit is set at 261 (314) pb at 95% confidence level, where the expected Standard Model cross-section for the ttbar process is 165^{+11}_{−16} pb.