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

Journal Article · Tue Sep 01 00:00:00 EDT 2009 · Physical Review. D, Particles Fields

DOI:https://doi.org/10.1103/PHYSREVD.80.052001· OSTI ID:21322550

Aaltonen, T; Maki, T; Mehtala, P; Orava, R; Osterberg, K; Saarikko, H; Remortel, N van ^[1]; Adelman, J; Brubaker, E; Fedorko, W T; Frisch, H J; Grosso-Pilcher, C; Kim, Y K; Krop, D; Kwang, S; Lee, H S; Paramonov, A A; Schmidt, M A; Shiraishi, S; Shochet, M ^[2]

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1. Division of High Energy Physics, Department of Physics, University of Helsinki and Helsinki Institute of Physics, FIN-00014, Helsinki (Finland)
2. Enrico Fermi Institute, University of Chicago, Chicago, Illinois 60637 (United States)

We have used the Collider Detector at Fermilab (CDF-II) to search for the flavor-changing neutral-current (FCNC) top-quark decay t{yields}Zc using a technique employing ratios of W and Z production, measured in pp data corresponding to an integrated luminosity of 1.52 fb{sup -1}. The analysis uses a comparison of two decay chains, pp{yields}tt{yields}WbWb{yields}l{nu}bjjb and pp{yields}tt{yields}ZcWb{yields}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 tt 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{yields}Zc) using a likelihood constructed from the llcjjb top-quark mass distribution and the number of l{nu}bjjb 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.

• OSTI ID: 21322550
• Journal Information: Physical Review. D, Particles Fields, Vol. 80, Issue 5; Other Information: DOI: 10.1103/PhysRevD.80.052001; (c) 2009 The American Physical Society; Country of input: International Atomic Energy Agency (IAEA); ISSN 0556-2821
• Country of Publication: United States
• Language: English

Related Subjects

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
B QUARKS
BRANCHING RATIO
CHAINS
COMPARATIVE EVALUATIONS
CROSS SECTIONS
EFFICIENCY
FERMILAB COLLIDER DETECTOR
FLAVOR MODEL
HELICITY
LEPTONS
LUMINOSITY
MASS
MASS DISTRIBUTION
NEUTRAL CURRENTS
PAIR PRODUCTION
PARTICLE DECAY
SIMULATION
STANDARD MODEL
T QUARKS
W MINUS BOSONS
W PLUS BOSONS
Z NEUTRAL BOSONS