# ${\boldsymbol {\boldsymbol t}}$-quark EW Couplings

${{\mathit W}}$ helicity fractions in top decays. ${{\mathit F}_{{0}}}$ is the fraction of longitudinal and ${{\mathit F}_{{+}}}$ the fraction of right-handed ${{\mathit W}}$ bosons. ${{\mathit F}_{{{V+A}}}}$ is the fraction of $\mathit V+\mathit A$ current in top decays. The effective Lagrangian (cited by ABAZOV 2008AI) has terms f${}^{L}_{1}$ and f${}^{R}_{1}$ for $\mathit V−\mathit A$ and $\mathit V+\mathit A$ couplings, f${}^{L}_{2}$ and f${}^{R}_{2}$ for tensor couplings with b$_{R}$ and b$_{L}$ respectively.

# ${\boldsymbol {\boldsymbol t}}$-quark FCNC Couplings $\kappa {}^{utg}/\Lambda$ and $\kappa {}^{ctg}/\Lambda$ INSPIRE search

VALUE (TeV${}^{-1}$) CL% DOCUMENT ID TECN  COMMENT
• • • We do not use the following data for averages, fits, limits, etc. • • •
$<0.0041$ 95 1
 2017 G
CMS $\vert {{\mathit \kappa}}{}^{tug}\vert /\Lambda$
$<0.018$ 95 1
 2017 G
CMS $\vert {{\mathit \kappa}}{}^{tcg}\vert /\Lambda$
$<0.0058$ 95 2
 2016 AS
ATLS ${{\mathit \kappa}}{}^{tug}/\Lambda$
$<0.013$ 95 2
 2016 AS
ATLS ${{\mathit \kappa}}{}^{tcg}/\Lambda$
$<0.0069$ 95 3
 2012 BP
ATLS ${{\mathit t}^{tug}}/{{\mathit \Lambda}}$ (${{\mathit t}^{tcg}}$ = 0)
$<0.016$ 95 3
 2012 BP
ATLS ${{\mathit t}^{tcg}}/{{\mathit \Lambda}}$ (${{\mathit t}^{tug}}$ = 0)
$<0.013$ 95 4
 2010 K
D0 ${{\mathit \kappa}}{}^{tug}/\Lambda$
$<0.057$ 95 4
 2010 K
D0 ${{\mathit \kappa}}{}^{tcg}/\Lambda$
$<0.018$ 95 5
 2009 N
CDF ${{\mathit \kappa}}{}^{tug}/\Lambda$ (${{\mathit \kappa}}{}^{tcg}$ = 0)
$<0.069$ 95 5
 2009 N
CDF ${{\mathit \kappa}}{}^{tcg}/\Lambda$ (${{\mathit \kappa}}{}^{tug}$ = 0)
$<0.037$ 95 6
 2007 V
D0 $\kappa {}^{utg}/\Lambda$
$<0.15$ 95 6
 2007 V
D0 $\kappa {}^{ctg}/\Lambda$
1  KHACHATRYAN 2017G based on 5.0 and 19.7 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ data at $\sqrt {s }$ = 7 and 8 TeV, respectively. ${{\mathit t}}$ -channel single top production is used. The result corresponds to B( ${{\mathit t}}$ $\rightarrow$ ${{\mathit u}}{{\mathit g}}$ ) $<$ $2.0 \times 10^{-5}$ or B( ${{\mathit t}}$ $\rightarrow$ ${{\mathit c}}{{\mathit g}}$ ) $<$ $4.1 \times 10^{-4}$.
2  AAD 2016AS based on 20.3 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ data at $\sqrt {s }$ = 8 TeV. The results are obtained from the 95$\%$ CL upper limit on the single top-quark production ${\mathit \sigma (}$ ${{\mathit q}}$ ${{\mathit g}}$ $\rightarrow$ ${{\mathit t}}{)}\cdot{}$B( ${{\mathit t}}$ $\rightarrow$ ${{\mathit b}}{{\mathit W}}$ ) $<$ 3.4 pb, B( ${{\mathit t}}$ $\rightarrow$ ${{\mathit u}}{{\mathit g}}$ ) $<$ $4.0 \times 10^{-5}$ and B( ${{\mathit t}}$ $\rightarrow$ ${{\mathit c}}{{\mathit g}}$ ) $<$ $20 \times 10^{-5}$.
3  Based on 2.05 fb${}^{-1}$ of ${{\mathit p}}{{\mathit p}}$ data at $\sqrt {s }$ = 7 TeV. The results are obtained from the 95$\%$ CL upper limit on the single top-quark production ${\mathit \sigma (}$ ${{\mathit q}}$ ${{\mathit g}}$ $\rightarrow$ ${{\mathit t}}{)}\cdot{}$B( ${{\mathit t}}$ $\rightarrow$ ${{\mathit b}}{{\mathit W}}$ ) $<$ 3.9 pb, for ${{\mathit q}}={{\mathit u}}$ or ${{\mathit q}}={{\mathit c}}$, B( ${{\mathit t}}$ $\rightarrow$ ${{\mathit u}}{{\mathit g}}$ ) $<$ $5.7 \times 10^{-5}$ and B( ${{\mathit t}}$ $\rightarrow$ ${{\mathit u}}{{\mathit g}}$ ) $<$ $2.7 \times 10^{-4}$.
4  Based on 2.3 fb${}^{-1}$ of data in ${{\mathit p}}{{\overline{\mathit p}}}$ collisions at $\sqrt {s }$ = 1.96 TeV. Upper limit of single top quark production cross section 0.20 pb and 0.27 pb via FCNC $\mathit t-u-g$ and $\mathit t-c-g$ couplings, respectively, lead to the bounds without assuming the absence of the other coupling. B( ${{\mathit t}}$ $\rightarrow$ ${{\mathit u}}{+}$ ${{\mathit g}}$ ) $<$ $2.0 \times 10^{-4}$ and B( ${{\mathit t}}$ $\rightarrow$ ${{\mathit c}}{+}$ ${{\mathit g}}$ ) $<$ $3.9 \times 10^{-3}$ follow.
5  Based on 2.2 fb${}^{-1}$ of data in ${{\mathit p}}{{\overline{\mathit p}}}$ collisions at $\sqrt {s }$ = 1.96 TeV. Upper limit of single top quark production cross section ${\mathit \sigma (}$ ${{\mathit u}{(c)}}$ ${+}$ ${{\mathit g}}$ $\rightarrow$ ${{\mathit t}}{)}$ $<$ 1.8 pb (95$\%$ CL) via FCNC $\mathit t-u-g$ and $\mathit t-c-g$ couplings lead to the bounds. B( ${{\mathit t}}$ $\rightarrow$ ${{\mathit u}}{+}$ ${{\mathit g}}$ ) $<$ $3.9 \times 10^{-4}$ and B( ${{\mathit t}}$ $\rightarrow$ ${{\mathit c}}{+}$ ${{\mathit g}}$ ) $<$ $5.7 \times 10^{-3}$ follow.
6  Result is based on 230 pb${}^{-1}$ of data at $\sqrt {s }$ = 1.96 TeV. Absence of single top quark production events via FCNC $\mathit t-u-g$ and $\mathit t-c-g$ couplings lead to the upper bounds on the dimensioned couplings, $\kappa {}^{utg}/\Lambda$ and $\kappa {}^{ctg}/\Lambda$, respectively.
References:
 KHACHATRYAN 2017G
JHEP 1702 028 Search for Anomalous ${{\mathit W}}{\mathit {\mathit t}}{\mathit {\mathit b}}$ Couplings and Flavour-Changing Neutral Currents in ${{\mathit t}}$-Channel Single Top Quark Production in ${{\mathit p}}{{\mathit p}}$ Collisions at $\sqrt {s }$ = 7 and 8 TeV
PL B712 351 Search for FCNC (flavour-changing neutral-currents) Single Top-Quark Production at $\sqrt {s }$ = 7 TeV with the ATLAS Detector
PL B693 81 Search for Flavor Changing Neutral Currents via Quark-Gluon Couplings in Single Top Quark Production using 2.3 ${\mathrm {fb}}{}^{-1}$ of ${{\mathit p}}{{\overline{\mathit p}}}$ Collisions
PRL 102 151801 Search for Top-Quark Production via Flavor-Changing Neutral Currents in ${{\mathit W}}$+1 Jet Events at CDF