We search for resonant production of ttbar in the lepton+jets decay channel. A matrix element reconstruction technique is used for each event a probability density function of the ttbar invariant mass is sampled.

These pdfs are used to construct a likelihood function, whereby the cross section for resonant ttbar production, given a hypothetical resonance mass and width, is estimated.

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 1500 GeV and widths equal to 1.2% of their mass.

We examine 4.8/fb of data and find no evidence of resonant production of ttbar candidate events.

We exclude at 95% CL a Z' with M_Z' < 900 GeV for Γ_Z' = 0.012 M_Z'

Mtt distribution from data vs expected SM background

Signal and dominant background templates

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

Yuri Oksuzian (last update July 22 2010) -- oksuzian@fnal.gov