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Search for the neutral current top quark decay t-->Zc using the ratio of Z-boson+4 jets to W-boson+4 jets production

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; ... Show more Show less
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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
Terms of use
Article is made available in accordance with the publisher's policy and may be subject to US copyright law. Please refer to the publisher's site for terms of use.
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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.
Date issued
2009-09
URI
http://hdl.handle.net/1721.1/51837
Department
Massachusetts Institute of Technology. Department of Physics; Massachusetts Institute of Technology. Laboratory for Nuclear Science
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
ISSN
1550-2368
1550-7998

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