Search for same-sign top-quark pair production at sqrt(s) = 7 TeV and limits on flavour changing neutral currents in the top sector

TL;DR

This paper reports a search for same-sign top-quark pairs at 7 TeV using CMS data, setting limits on flavor-changing neutral currents that challenge certain new physics explanations for observed asymmetries.

Contribution

It provides the first experimental limits on same-sign top-quark production and FCNC couplings at 7 TeV, constraining models with a Z' boson.

Findings

No significant excess observed in same-sign top-quark pairs.

Limits set on Z' mass and couplings disfavor FCNC explanations for Tevatron asymmetries.

Constraints improve understanding of top-sector new physics.

Abstract

An inclusive search for same-sign top-quark pair production in pp collisions at sqrt(s) = 7 TeV is performed using a data sample recorded with the CMS detector in 2010, corresponding to an integrated luminosity of 35 inverse picobarns. This analysis is motivated by recent studies of p p-bar to t t-bar reporting mass-dependent forward-backward asymmetries larger than expected from the standard model. These asymmetries could be due to Flavor Changing Neutral Currents (FCNC) in the top sector induced by t-channel exchange of a massive neutral vector boson (Z'). Models with such a Z' also predict enhancement of same-sign top-pair production in pp or p p-bar collisions. Limits are set as a function of the Z' mass and its couplings to u and t quarks. These limits disfavour the FCNC interpretation of the Tevatron results.