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

• Main Authors: Xie, Si (Contributor), Makhoul, K. (Contributor), Knuteson, Bruce O. (Contributor), Henderson, C. (Contributor), Hahn, Kristian Allan (Contributor), Goncharov, M. (Contributor), Gomez-Ceballos, Guillelmo (Contributor), Choudalakis, Georgios (Contributor), Bauer, Gerry P. (Contributor), Paus, Christoph M. E. (Contributor)
• Other Authors: Massachusetts Institute of Technology. Department of Physics (Contributor), Massachusetts Institute of Technology. Laboratory for Nuclear Science (Contributor)
• Format: Article
• Language: English
• Published: American Physical Society, 2010-02-26T19:35:40Z.
• Subjects: Article
• Online Access: Get fulltext

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.
Academy of Finland
Slovak R&D Agency
Programa Consolider-Ingenio 2010, Spain
Ministerio de Ciencia e Innovación, Spain
Russian Foundation for Basic Research
Institut National de Physique Nucleaire et Physique des Particules/CNRS
Royal Society, United Kingdom
Science and Technology Facilities Council, United Kingdom
Korean Research Foundation
Korean Science and Engineering Foundation
Bundesministerium für Bildung und Forschung, Germany
Alfred P. Sloan Foundation
Swiss National Science Foundation
National Science Council of the Republic of China
Natural Sciences and Engineering Research Council of Canada
Ministry of Education, Culture, Sports, Science and Technology of Japan
Italian Istituto Nazionale di Fisica Nucleare
National Science Foundation
United States Department of Energy