Search for Heavy Top t'>Wq In Lepton Plus Jets Events

Contents:
Introduction
We search for the heavy top (t') quark pair production decaying to Wq
final states in 2.8 fb^{1} of the CDF Run 2 data sample of
lepton+jets (no btagging requirements). We reconstruct the mass of the
t' quark and perform a 2Dfit of the observed (H_{T},M_{reco})
distribution to discriminate the new physics signal from standard model
backgrounds. H_{T} is defined here as the
sum of the Jet E_{T}s, lepton E_{T} and Missing E_{T}. M_{reco} is the
reconstructed mass of the t'.
We assume that the t' quark
The search has
theoretical motivation from several different sources.
m_{t'}  Q^{2} 
(GeV) 
(pb) 
180 
0.065 
200 
0.044 
220 
0.021 
240 
0.011 
260 
0.013 
280 
0.009 
300 
0.007 
320 
0.005 
340 
0.006 
360 
0.005 
380 
0.003 
400 
0.003 
450 
0.003 
500 
0.002 
m_{t'}  IFSR  

(GeV)  offset 
slope 
180  0.125 
0.026 
200  0.125 
0.024 
220  0.125 
0.022 
240  0.110 
0.020 
260  0.080 
0.018 
280  0.060 
0.017 
300  0.035 
0.014 
320  0.025 
0.011 
340 
0.015 
0.009 
360 
0.010 
0.008 
380 
0.007 
0.007 
400 
0.005 
0.006 
450 
0.004 
0.005 
500 
0.003 
0.004 
mass 
positive uncertainty 
negative uncertainty 
top 

175 
+0.007 
0.008 
t' 

180 
+0.007 
0.008 
200 
+0.004 
0.005 
220 
+0.005 
0.005 
240 
+0.003 
0.003 
260 
+0.003 
0.003 
280 
+0.002 
0.003 
300 
+0.001 
0.003 
320 
+0.001 
0.002 
340 
+0.002 
0.002 
360 
+0.003 
0.002 
380 
+0.002 
0.002 
400 
+0.005 
0.002 
450 
+0.004 
0.005 
500 
+0.015 
0.013 
m_{t'}  Expected Limit (pb)  Observed  

(GeV)  2.3%  15.9%  median  84.1%  97.7%  Limit (pb) 
180 
1.900 
2.362 
2.954 
3.772 
4.540 
3.759 
200 
1.066 
1.434 
1.959 
2.828 
3.682 
1.595 
220 
0.360 
0.486 
0.693 
1.002 
1.579 
0.355 
240 
0.248 
0.306 
0.406 
0.558 
0.743 
0.258 
260 
0.183 
0.216 
0.288 
0.390 
0.498 
0.254 
280 
0.135 
0.161 
0.208 
0.280 
0.370 
0.237 
300 
0.089 
0.116 
0.150 
0.202 
0.268 
0.188 
320 
0.063 
0.081 
0.112 
0.156 
0.202 
0.165 
340 
0.050 
0.064 
0.088 
0.120 
0.164 
0.133 
360 
0.041 
0.050 
0.070 
0.096 
0.128 
0.112 
400 
0.031 
0.040 
0.056 
0.077 
0.103 
0.109 
450 
0.020 
0.025 
0.033 
0.045 
0.058 
0.083 
500 
0.019 
0.022 
0.028 
0.039 
0.055 
0.073 
Distributions of H_{T} (left) and M_{reco} (right) showing result of the no signal fit. 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.  
(epsf) 
(epsf) 
Distributions of H_{T} (left) and M_{reco}
(right)
showing distributions with
t' mass of 450 GeV (the t' mass sample with the higest likelihood).
Using the t' cross section at which the likelihood was maximized. 

(EPS) 
(EPS) 
2Ddistribution of H_{T} and M_{reco} of data (black circles) and the fitted number of background events: QCD (purple circle), W+jets (light green squares) and top (blue triangles). 
(EPS) 
As in the previous version of the
analysis, in order to
estimate possible excess of events in the tails
of
H_{T} and M_{reco}
we count the number of events in groups of n x n of
our standard 25 GeV bins in these quantities, and compare the number
predicted from a zerosignal fit to the full two dimensional
spectrum with the number seen in data. For each nxn bin one can then
calculate the pvalue for
having observed that number or greater, given the prediction. The most significant n x n bin is that where n = 10; the probablility for observing 29 or more events given 18.03 expected is 0.01 (Assuming systematic uncertainty on the background). 
(eps) 