Search for the neutral current top quark decay t-->Zc using the ratio of Z-boson+4 jets to W-boson+4 jets production
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Aaltonen-2009-Search for the neutr.pdf
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Author(s)
Xie, Si
Knuteson, Bruce O.
Henderson, C.
Hahn, Kristian Allan
Gomez-Ceballos, Guillelmo
Choudalakis, Georgios
Paus, Christoph M. E.
Makhoul, Khaldoun
Goncharov, Maxim
Bauer, Gerry P
Alternative Title
Search for the neutral current top quark decay t→Zc using the ratio of Z-boson+4 jets to W-boson+4 jets production
Date Issued
September 2009
Journal
Physical Review D
Publisher
American Physical Society
Citation
CDF Collaboration et al. “Search for the neutral current top quark decay t-->Zc using the ratio of Z-boson+4 jets to W-boson+4 jets production.” Physical Review D 80.5 (2009): 052001. © 2009 The American Physical Society
Version
Final published version
Abstract
We have used the Collider Detector at Fermilab (CDF-II) to search for the flavor-changing neutral-current (FCNC) top-quark decay t→Zc using a technique employing ratios of W and Z production, measured in pp̅ data corresponding to an integrated luminosity of 1.52 fb[superscript -1]. The analysis uses a comparison of two decay chains, pp̅ →tt̅ →WbWb→ℓνbjjb and pp̅ →tt̅ →ZcWb→ℓℓcjjb, to cancel systematic uncertainties in acceptance, efficiency, and luminosity. We validate the modeling of acceptance and efficiency for lepton identification over the multiyear data set using another ratio of W and Z production, in this case the observed ratio of inclusive production of W to Z bosons. To improve the discrimination against standard model backgrounds to top-quark decays, we calculate the top-quark mass for each event with two leptons and four jets assuming it is a tt̅ event with one of the top quarks decaying to Zc. For additional background discrimination we require at least one jet to be identified as originating from a b quark. No significant signal is found and we set an upper limit on the FCNC branching ratio Br(t→Zc) using a likelihood constructed from the ℓℓcjjb top-quark mass distribution and the number of ℓνbjjb events. Limits are set as a function of the helicity of the Z boson produced in the FCNC decay. For 100% longitudinally-polarized Z bosons we find limits of 8.3% and 9.3% (95% C.L.) depending on the assumptions regarding the theoretical top-quark pair production cross section.
MIT Department
Massachusetts Institute of Technology. Department of Physics
Massachusetts Institute of Technology. Laboratory for Nuclear Science
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DOI of Published Version
http://dx.doi.org/10.1103/PhysRevD.80.052001
