Search for anomalous single top quark production in association with a photon in pp collisions at sqrt(s) = 8 TeV

TL;DR

This study searches for flavor changing neutral currents involving single top quark production with a photon at 8 TeV, setting the most stringent limits to date on related anomalous couplings and decay branching fractions.

Contribution

It provides the first comprehensive search for FCNC in single top plus photon production at 8 TeV, establishing new upper limits on anomalous couplings and decay rates.

Findings

No evidence of FCNC single top production was observed.

Upper limits on B(t to u gamma) and B(t to c gamma) were set.

Most stringent limits on these processes to date.

Abstract

The result of a search for flavor changing neutral currents (FCNC) through single top quark production in association with a photon is presented. The study is based on proton-proton collisions at a center-of-mass energy of 8 TeV using data collected with the CMS detector at the LHC, corresponding to an integrated luminosity of 19.8 inverse femtobarns. The search for t gamma events where t to Wb and W to mu nu is conducted in final states with a muon, a photon, at least one hadronic jet with at most one being consistent with originating from a bottom quark, and missing transverse momentum. No evidence of single top quark production in association with a photon through a FCNC is observed. Upper limits at the 95% confidence level are set on the tu gamma and tc gamma anomalous couplings and translated into upper limits on the branching fraction of the FCNC top quark decays: B(t to u gamma) < 1.3E-4 and B(t to c gamma) < 1.7E-3. Upper limits are also set on the cross section of associated t gamma production in a restricted phase-space region. These are the most stringent limits currently available.