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

Authors

T. Aaltonen, Helsingin Yliopisto
J. Adelman, The Enrico Fermi Institute
T. Akimoto, University of Tsukuba
B. Alvarez González, Universidad de Cantabria
S. Amerio, Istituto Nazionale Di Fisica Nucleare, Sezione di Padova
D. Amidei, University of Michigan, Ann Arbor
A. Anastassov, Northwestern University
A. Annovi, INFN, Laboratori Nazionali Di Frascati
J. Antos, Univerzita Komenského v Bratislave
G. Apollinari, Fermi National Accelerator Laboratory
A. Apresyan, Purdue University
T. Arisawa, Waseda University
A. Artikov, Joint Institute for Nuclear Research, Dubna
W. Ashmanskas, Fermi National Accelerator Laboratory
A. Attal, Universitat Autònoma de Barcelona
A. Aurisano, Texas A&M University
F. Azfar, University of Oxford
P. Azzurri, Istituto Nazionale di Fisica Nucleare, Sezione di Pisa
W. Badgett, Fermi National Accelerator Laboratory
A. Barbaro-Galtieri, Lawrence Berkeley National Laboratory
V. E. Barnes, Purdue University
B. A. Barnett, Johns Hopkins University
V. Bartsch, University College London
G. Bauer, Massachusetts Institute of Technology
P. H. Beauchemin, Université McGill
F. Bedeschi, Istituto Nazionale di Fisica Nucleare, Sezione di Pisa
D. Beecher, University College London
S. Behari, Johns Hopkins University

Document Type

Article

Publication Date

9-8-2009

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 pp̄ data corresponding to an integrated luminosity of 1.52fb-1. The analysis uses a comparison of two decay chains, pp̄→tt̄→WbWb→νbjjb and pp̄→tt̄→ZcWb→cjjb, 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 tt̄ 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 cjjb top-quark mass distribution and the number of νbjjb 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. © 2009 The American Physical Society.

Publication Source (Journal or Book title)

Physical Review D - Particles, Fields, Gravitation and Cosmology

Recommended Citation

Aaltonen, T., Adelman, J., Akimoto, T., Alvarez González, B., Amerio, S., Amidei, D., Anastassov, A., Annovi, A., Antos, J., Apollinari, G., Apresyan, A., Arisawa, T., Artikov, A., Ashmanskas, W., Attal, A., Aurisano, A., Azfar, F., Azzurri, P., Badgett, W., Barbaro-Galtieri, A., Barnes, V., Barnett, B., Bartsch, V., Bauer, G., Beauchemin, P., Bedeschi, F., Beecher, D., & Behari, S. (2009). Search for the neutral current top quark decay t→Zc using the ratio of Z-boson+4jets to W-boson+4jets production. Physical Review D - Particles, Fields, Gravitation and Cosmology, 80 (5) https://doi.org/10.1103/PhysRevD.80.052001