Abstract
We have used the Collider Detector at Fermilab (CDF-II) to search for the flavor-changing neutral-current (FCNC) top-quark decay using a technique employing ratios of and production, measured in data corresponding to an integrated luminosity of . The analysis uses a comparison of two decay chains, and , 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 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 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.
6 More- Received 4 May 2009
DOI:https://doi.org/10.1103/PhysRevD.80.052001
©2009 American Physical Society