43 research outputs found
Search for the Neutral Current Top Quark Decay t-->Zc Using the Ratio of Z-Boson + 4 Jets to W-Boson + 4 Jets Production
We have used the Collider Detector at Fermilab (CDF II) to search for the
flavor-changing neutral-current (FCNC) top quark decay {t\goes Zc} using a
technique employing ratios of and production, measured in \ppbar data
corresponding to an integrated luminosity of 1.52 . The analysis uses
a comparison of two decay chains, {p\bar{p}\goes t\bar{t}\goes
WbWb\goes\ell\nu bjjb} and {p\bar{p}\goes t\bar{t}\goes ZcWb\goes\ell\ell
cjjb}, to cancel systematic uncertainties in acceptance, efficiency, and
luminosity. We validate the modeling of acceptance and efficiency for lepton
identification over the multi-year dataset using another ratio of and
production, in this case the observed ratio of inclusive production of to
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 event with one of the top
quarks decaying to . For additional background discrimination we require at
least one jet to be identified as originating from a -quark. No significant
signal is found and we set an upper limit on the FCNC branching ratio
Br({t\goes Zc}) using a likelihood constructed from the top
quark mass distribution and the number of events. Limits are
set as a function of the helicity of the boson produced in the FCNC decay.
For 100% longitudinally polarized 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
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