CDF t' Search Public page

Search for Heavy Top t'->Wq In Lepton Plus Jets Events
in 760 pb^-1
J. Conway, R. Erbacher, A. Ivanov
University of California, Davis
A. Lath
Rutgers University
R. Roser
Fermilab
R. Hughes, K. Lannon, B. Winer
Ohio State University

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 (H_T,M_reco) distribution to discriminate the new physics signal from Standard Model backgrounds.

We exclude Standard Model fourth-generation t' quark with mass below 256 GeV at 95% CL.

CDF public conference note
pdf

	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)
(EPS)

m_t'	Expected Limit (pb)					Observed
(GeV)	2.3%	15.9%	median	84.1%	97.7%	Limit (pb)
175	2.863	3.268	4.017	4.961	6.437	5.205
200	1.753	1.902	2.362	2.968	3.769	2.569
225	1.052	1.109	1.338	1.700	2.153	1.132
250	0.620	0.657	0.799	1.026	1.313	0.720
275	0.432	0.457	0.555	0.717	0.906	0.595
300	0.304	0.321	0.394	0.503	0.657	0.412
350	0.189	0.198	0.241	0.315	0.408	0.322
400	0.134	0.138	0.167	0.213	0.281	0.252

Distributions of H_T (left) and M_reco (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.


(EPS)	(EPS)

2D-distribution of H_T and M_reco 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.


(EPS)	(EPS)

In order to estimate possible excess of events in the tails of H_T and M_reco 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.
We also use our likelihood as a goodness-of-fit by drawing pseuodexperiments from SM distributions. We obtain that 31% of pseudoexperiments are less likely than data.


(EPS)	(EPS)

	"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.
(EPS)

Event Displays of four high-mass events

(EPS)

Last modified on 06/27/07 by Andrew Ivanov

Search for Heavy Top t'->Wq In Lepton Plus Jets Events in 760 pb-1 J. Conway, R. Erbacher, A. Ivanov University of California, Davis A. Lath Rutgers University R. Roser Fermilab R. Hughes, K. Lannon, B. Winer Ohio State University

We exclude Standard Model fourth-generation t' quark with mass below 256 GeV at 95% CL.

CDF public conference note pdf

Event Displays of four high-mass events

Search for Heavy Top t'->Wq In Lepton Plus Jets Events
in 760 pb^-1
J. Conway, R. Erbacher, A. Ivanov
University of California, Davis
A. Lath
Rutgers University
R. Roser
Fermilab
R. Hughes, K. Lannon, B. Winer
Ohio State University

CDF public conference note
pdf