A measurement of the W boson helicity is presented, where the W boson originates from the decay of a top quark produced in pp collisions. The event selection, optimized for reconstructing a single top quark in the final state, requires exactly one isolated lepton (muon or electron) and exactly two jets, one of which is likely to originate from the hadronization of a bottom quark. The analysis is performed using data recorded at a center-of-mass energy of 8 TeV with the CMS detector at the CERN LHC in 2012. The data sample corresponds to an integrated luminosity of 19.7 fb$^{-1}$. The measured helicity fractions are F$_{L}$ = 0.298 " 0.028 (stat) " 0.032(syst), F$_{0}$ = 0.720 " 0.039 (stat) " 0.037(syst), and F$_{R}$ = -0.018 " 0.019 (stat) " 0.011(syst). These results are used to set limits on the real part of the tWb anomalous couplings, g$_{L}$ and g$_{R}$.

The W boson helicity fractions from top quark decays in t-tbar events are measured using data from proton-proton collisions at a centre-of-mass energy of 8 TeV. The data were collected in 2012 with the CMS detector at the LHC, corresponding to an integrated luminosity of 19.8 inverse-femtobarns. Events are reconstructed with either one muon or one electron, along with four jets in the final state, with two of the jets being identified as originating from b quarks. The measured helicity fractions from both channels are combined, yielding F[0] = 0.681 +/- 0.012 (stat) +/- 0.023 (syst), F[L] = 0.323 +/- 0.008 (stat) +/- 0.014 (syst), and F[R] = -0.004 +/- 0.005 (stat) +/- 0.014 (syst) for the longitudinal, left-, and right-handed components of the helicity, respectively. These measurements of the W boson helicity fractions are the most accurate to date and they agree with the predictions from the standard model.

Precise measurements of the properties of the top quark allow for testing the Standard Model (SM) and can be used to constrain new physics models. The top quark is predicted in the SM to decay almost exclusively to a W boson and b-quark. Thus, studying the Wtb vertex structure at high precision and in detail is motivated. This thesis presents a measurement of the W boson helicity fractions in top quark decays with top/anit-top events in the lepton + jets final state using proton-proton collisions at a centre-of-mass energy of 8 TeV recorded in 2012 with the ATLAS detector at the LHC. The da...

The authors present a measurement of the fractions F0 and F+ of longitudinally polarized and right-handed W bosons in top quark decays using data collected with the CDF II detector. The data set used in the analysis corresponds to an integrated luminosity of approximately 318 pb−1. They select t{bar t} candidate events with one lepton, at least four jets, and missing transverse energy. The helicity measurement uses the decay angle [theta]*, which is defined as the angle between the momentum of the charged lepton in the W boson rest frame and the W momentum in the top quark rest frame. The cos [theta]* distribution in the data is determined by full kinematic reconstruction of the t{bar t} candidates. They find F0 = 0.85{sub -0.22}{sup +0.15}(stat)±0.06(syst) and F+ = 0.05{sub -0.05}{sup +0.11}(stat) ± 0.03(syst), which is consistent with the standard model prediction. They set an upper limit on the fraction of right-handed W bosons of F+

We present a measurement of the helicity of the W boson produced in top quark decays using t{bar t} decays in the l+jets and dilepton final states selected from a sample of 5.4 fb−1 of collisions recorded using the D0 detector at the Fermilab Tevatron p{bar p} collider. We measure the fractions of longitudinal and right-handed W bosons to be f0 = 0.669 ± 0.102 [±0.078 (stat.) ± 0.065 (syst.)] and f+ = 0.023 ± 0.053 [±0.041 (stat.)±0.034 (syst.)], respectively. This result is consistent at the 98% level with the standard model. A measurement with f0 fixed to the value from the standard model yields f+ = 0.010 ± 0.037 [±0.022 (stat.) ± 0.030 (syst.)].

We present a measurement of the fractions F0 and F+ of longitudinally polarized and right-handed W bosons in top-quark decays using data collected with the CDF II detector. The data set used in the analysis corresponds to an integrated luminosity of approximately 955 pb−1. We select t{bar t} candidate events with one lepton, at least four jets, and missing transverse energy. Our helicity measurement uses the decay angle [theta]*, which is defined as the angle between the momentum of the charged lepton in the W boson rest-frame and the W momentum in the top-quark rest-frame. The cos[theta]* distribution in the data is determined by full kinematic reconstruction of the t{bar t} candidates. We find F0= 0.59 ± 0.12(stat){sup +0.07}{sub -0.06}(syst) and F+=-0.03 ± 0.06(stat){sup +0.04}{sub -0.03}(syst), which is consistent with the standard model prediction. We set an upper limit on the fraction of right-handed W bosons of F+ ≤ 0.10 at the 95% confidence level.

A measurement of the fraction, f+, of right-handed W bosons produced in top quark decays is presented. This analysis is based on a sample corresponding to an integrated luminosity of 370 pb−1, collected by the D0 detector at the Fermilab Tevatron p{bar p} Collider at √s = 1.96 TeV. The helicity angle, [theta]*, is reconstructed for each lepton. f+ is determined by comparing the cos [theta]* distribution from the data with that for the expected background and signal for various values of f+. The fraction of longitudinal W bosons, f°, is assumed to be 0.7 as predicted by the standard model. This yields f+ = 0.109 ± 0.094 (stat) ± 0.063 (syst), consistent with the standard model prediction of f+ = 3.6x 10−4. The possibility that both f+ and f° stray from standard model values is also investigated. In this case cos [theta]* distributions for each possible W helicity state, along with the backgrounds, are fit to the cos [theta]* distribution for the data. The best fit values are f+ = 0.82 ± 0.30(stat) and f° = -0.58 ± 0.50(stat).