Search for top-quark production via flavor-changing neutral currents in W+1 jet events at CDF

TL;DR

This study searches for rare top-quark production via flavor-changing neutral currents in proton-antiproton collisions, finding no evidence and setting upper limits on production cross sections and branching ratios.

Contribution

First search for FCNC top-quark production in W+1 jet events at CDF, using neural networks to classify events and establish upper limits.

Findings

No evidence for FCNC top-quark production.

Set upper limit on cross section: < 1.8 pb.

Derived upper limits on branching ratios: BR(t->u+g)<3.9e-4, BR(t->c+g)<5.7e-3.

Abstract

We report on the first search for top-quark production via flavor-changing neutral-current (FCNC) interactions in the non-standard-model process u(c)+g -> t using ppbar collision data collected by the CDF II detector. The data set corresponds to an integrated luminosity of 2.2/fb. The candidate events feature the signature of semileptonic top-quark decays and are classified as signal-like or background-like by an artificial neural network trained on simulated events. The observed discriminant distribution is in good agreement with the one predicted by the standard model and provides no evidence for FCNC top-quark production, resulting in a Bayesian upper limit on the production cross section sigma (u(c)+g -> t) < 1.8 pb at the 95% confidence level. Using theoretical predictions we convert the cross-section limit to upper limits on FCNC branching ratios: BR (t -> u+g) < 3.9 x 10{-4}$ and BR (t -> c+g) < 5.7 x 10^{-3}.