Search for Heavy Top t'->Wq In Lepton Plus Jets Events
We search for the heavy top (t') quark pair production decaying to Wq final states in 760 pb-1 of the CDF Run 2 data sample of lepton+jets. We reconstruct the mass of the t' quark and perform a 2D-fit of the observed (HT,Mreco) distribution to discriminate the new physics signal from Standard Model backgrounds.
|Upper limit, at 95% CL, on the production rate for t' as a function of t' mass (red). The purple curve is a theoretical cross section. The blue band represents +/-1 standard deviation expectation limit (light blue corresponds to +/- 2 standard deviation)|
|mt'||Expected Limit (pb)||Observed|
Distributions of HT (left) and Mreco (right) showing result of the fit for m(t')=250 GeV. The normalizations of the various sources and distortions of kinematic distributions due to systematic effects are those corresponding to the maximum likelihood when the cross section for t' is set to its 95% CL upper limit.
2D-distribution of HT and Mreco of data and simulated physics processes for m(t')=250 GeV (left) and m(t')=400 GeV (right). Number of points in scattered distributions of physics processes correspond to 10 times more data (100 times more for m(t')=400 GeV ). Dashed line represent the fitting box. The ticks at the axes represent the binning used in the fit. The edge bins are overflow bins and include information outside of the box.
In order to estimate possible excess of events in the tails of
HT and Mreco
we a-priori selected signal box (the area outside of dashed region
in the left plot)
with ~ 1% of SM events.
We expect 6.8 events from SM processes, and observe 7.
|"Temperature" plot showing the significance of observed deviation from the expectation (blue is the deficit, and red is the excess of events) in each bin.|