Search for anomalous Wtb couplings and flavour-changing neutral currents in t-channel single top quark production in pp collisions at $\sqrt{s}$ = 7 and 8 TeV

Abstract

Single top quark events produced in the t channel are used to set limits on anomalous Wtb couplings and to search for top quark flavour-changing neutral current (FCNC) interactions. The data taken with the CMS detector at the LHC in proton-proton collisions at $\sqrt{s}$ = 7 and 8 TeV correspond to integrated luminosities of 5.0 and 19.7 $fb^{−1}$, respectively. The analysis is performed using events with one muon and two or three jets. A Bayesian neural network technique is used to discriminate between the signal and backgrounds, which are observed to be consistent with the standard model prediction. The 95% confidence level (CL) exclusion limits on anomalous right-handed vector, and left- and right-handed tensor Wtb couplings are measured to be |$f_{V}$$^{R}$| < 0.16, |$f_T$$^L$| < 0.057, and − 0.049 < $f_T$$^R$ < 0.048, respectively. For the FCNC couplings $κ_{tug}$ and $κ_{tcg}$, the 95% CL upper limits on coupling strengths are $|κ_{tug}|/Λ < 4.1 × 10^{−3} TeV^{−1}$ and $|κ_{tcg}|/Λ < 1.8 × 10^{−2} TeV^{−1}$, where Λ is the scale for new physics, and correspond to upper limits on the branching fractions of $2.0 × 10^{−5}$ and$ 4.1 × 10^{−4}$ for the decays t → ug and t → cg, respectively.