We present a blind search for resonant top-antitop pair production  and subsequent decay in the all-hadronic channel. We apply a powerful reconstruction technique where the observed event kinematics are constrained according to the full standard model top-antitop production and decay matrix element.

Probability density from the per-event matrix element calculation is used as discriminant to reduce and control the large backgrounds of the all-hadronic channel. The discriminant serves as an input to neural net with other kinematic variables.

We test Mtt spectrum for possible resonant production using a Bayesian approach that yields the posterior probability that the data contains resonant events produced with a given mass and a given cross section.

We compare the 95% C.L. points for these posterior probabilities for the data with those expected from SM sources only and determine how likely it is for the SM to fluctuate to the data for each mass point. A very unlikely fluctuation could then indicate the presence of New Physics in the sample.

We test for vector resonances with masses between 450 and 900 GeV and widths equal to 1.2% of their mass. We select events with 6,7 jets and 1 or 2 tags. The dataset corresponds to an integrated luminosity of 2.8 fb-1.

The data is consistent with the Standard Model and we can set the limit on Z' production at 805GeV.

Mtt distribution from data vs expected SM background in the >400 GeV search region

Mtt distribution from data vs expected SM background in the >400 GeV search region(fine binning)

95% CL upper limits on the cross section for resonance production

Yuri Oksuzian (last update June 2nd 2009) -- oksuzian@fnal.gov