Search for Anomalous Single Top Quark Production in Association with a Photon in $pp$ Collisions at $ \sqrt{s}=8 $ TeV

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 fb$^{−1}$. The search for tγ events where t → Wb and W → μν 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 tuγ and tcγ anomalous couplings and translated into upper limits on the branching fraction of the FCNC top quark decays: ℬ(t → uγ) < 1.3 × 10$^{− 4}$ and ℬ(t → cγ) < 1.7 × 10$^{− 3}$. Upper limits are also set on the cross section of associated tγ production in a restricted phase-space region. These are the most stringent limits currently available.