Anomalous Couplings Of Top Quark Research Articles

Top quark anomalous couplings at the high-luminosity phase of the LHC

The combination of the latest and most precise measurements of several top quark properties is presented in this paper in order to establish allowed regions on anomalous contributions to the Lorentz structure of the Wtb vertex. These measurements include single top production cross-sections, W boson helicity fractions and forward–backward asymmetries, both at Tevatron and at the Large Hadron Collider (LHC), up to a center-of-mass energy of 13 TeV. The results obtained at 95% Confidence Level (CL) for the top quark anomalous couplings are compared with the limits extracted from a combination that includes the expected measurements at the future High-Luminosity run of the LHC.

Top quark anomalous electromagnetic couplings in photon-photon scattering at the LHC

The capability of the LHC to study the electromagnetic dipole moments of the top quark is discussed. In particular, the process $pp\to p\gamma\gamma p\to pt\bar{t}p$, which is supposed to be tagged by the forward/backward detectors at the LHC experiments, is used to explore the top quark electric and magnetic moments. We perform analytical calculations and then a numerical analysis on the sensitivity of the total cross section of the top quark pair production in $\gamma\gamma$ scattering at the LHC to the anomalous top quark couplings with photon. It is shown that improvements in the bounds on the electromagnetic dipole moments of the top quark can be achieved in this channel in comparison with the constraints from the former studies.

Weak interactions in top-quark pair production at hadron colliders: An update

Weak corrections for top-quark pair production at hadron colliders are revisited. Predictions for collider energies of 8 TeV, adopted to the recent LHC run, and for 13 as well as 14 TeV, presumably relevant for the next round of LHC experiments, are presented. Kinematic regions with large momentum transfer are identified, where the corrections become large and may lead to strong distortions of differential distributions, thus mimicking anomalous top-quark couplings. As a complementary case we investigate the threshold region, corresponding to configurations with small relative velocity between top and antitop quarks, which is particularly sensitive to the top-quark Yukawa coupling. We demonstrate, that nontrivial upper limits on this coupling, complementary to those recently derived by the CMS and the ATLAS collaborations, are well within reach of ongoing experiments. We, furthermore, suggest a prescription that allows the implementation of these corrections in current Monte Carlo generators. Furthermore, the weak corrections have been included in the publicly available hathor library. The numerical results presented in this article use the same setup as the recently calculated next-to-next-to-leading-order QCD corrections. The results can thus be combined to give the most precise theoretical predictions.

Top quark couplings and polarization

Precise measurements of top quark couplings are presented. The measurements cover the single top tW cross section, the top-quark branching-fraction ratio R=B(t → Wb)/B(t → Wq) and the CKM matrix element Vtb from the single top cross sections. Top quark polarisation in the t-channel single-top quark production and dilepton tt, and W-helicity fraction measurements along with searches of top quark anomalous couplings in lepton plus jet channel are also presented. Finally measurements of top quark pair production in association with a W or Z boson or a photon are presented.

Anomalous top-quark coupling effects in rare B and K decays

The Large Hadron Collider at CERN is performing direct searches for top-quark anomalous flavor-changing neutral current (FCNC) processes. However, these processes may be correlated closely with the low-energy rare $$B$$ and $$K$$ meson decays. In this paper, we review the anomalous top-quark coupling effects in these low-energy flavor transitions, summarize the flavor constraints and discuss their implications for direct detection of top-FCNC processes at the Large Hadron Collider.

Anomalous Higgs-boson coupling effects inHW+W−production at the LHC

We study the LHC associated production of a Higgs boson and a ${W}^{+}{W}^{\ensuremath{-}}$ vector-boson pair at 14 TeV, in the standard model and beyond. We consider different signatures corresponding to the cleanest $H$ and $W$ decay channels and discuss the potential of the high-luminosity phase of the LHC. In particular, we investigate the sensitivity of the $H{W}^{+}{W}^{\ensuremath{-}}$ production to possible anomalous Higgs couplings to vector bosons and fermions. Since the $b$-quark initiated partonic channel contributes significantly to this process, we find a moderate sensitivity to both the size and sign of an anomalous top-quark Yukawa coupling, because perturbative unitarity in the standard model implies a destructive interference in the $b\overline{b}$ subprocess. We show that a combination of various signatures can reach $\ensuremath{\sim}9$ standard-deviation sensitivity in the presently allowed negative region of the top-Higgs coupling, if not previously excluded.

Associated production of single top quark and W boson through anomalous couplings at LHeC based γp colliders

We consider the production of a single top quark in association with a W boson at LHeC based γp collider. We compute the cross-section for the process γp→WtX with the anomalous Wtb and Wtbγ couplings. We find that the sensitivities to anomalous couplings of top quark are shown to be comparable, even better than the ones obtained from direct searches at hadron colliders.

Probing the Top Quark Flavour-Changing Neutral Current at a Future Electron-Positron Collider

We present a study to examine the sensitivity of a futuree-e+collider to the anomalous top flavour-changing neutral current (FCNC) to the gluon. To separate signal from background a multivariate analysis is performed on top quark pair and background events, where one top quark is considered to follow the dominant standard model (SM) decay,t→Wb, and the other top decays through FCNC,t→qg, whereqis au- or ac-quark. The analysis of fully hadronic FCNC decay of thett-pair is also presented. The 95% confidence level limits on the top quark anomalous couplings are obtained for different values of the center-of-mass energies and integrated luminosities.

Probing Anomalous Top Quark Couplings in Diffractive Events at the LHC

Probing Anomalous Top Quark Couplings in Diffractive Events at the LHC

A like-sign dimuon charge asymmetry at tevatron induced by anomalous top quark couplings

We show that the recently measured 3.9 σ deviations of the charge asymmetry of like-sign dimuon events from the standard model prediction by the D0 collaboration at Tevatron can be explained by introducing the anomalous right-handed top quark couplings. A combined analysis with the \(B_s - \bar B_s\) and the \(B_d - \bar B_d\) mixings, B → X sγ decays and the time-dependent CP asymmetry in B → φK decays has been performed. The anomalous tsW couplings are preferred to explain the dimuon charge asymmetry together with other CP violating observables.

CP-odd correlations using jet momenta fromtt¯events at the Tevatron

We discuss T-odd correlations between jet and lepton momenta in tt_bar events at the Tevatron that can be used to search for CP violation. We identify correlations suitable for the lepton plus jets and purely hadronic top-quark pair decay channels. As an example of CP violation we consider the top-quark anomalous couplings, including its chromo-electric dipole moment, and we estimate the limits that can be placed at the Tevatron.

CPviolating anomalous top-quark couplings at the LHC

We study the $T$ odd correlations induced by $CP$ violating anomalous top-quark couplings at both production and decay level in the process $gg\ensuremath{\rightarrow}t\overline{t}\ensuremath{\rightarrow}(b{\ensuremath{\mu}}^{+}{\ensuremath{\nu}}_{\ensuremath{\mu}})(\overline{b}{\ensuremath{\mu}}^{\ensuremath{-}}{\overline{\ensuremath{\nu}}}_{\ensuremath{\mu}})$. We consider several counting asymmetries at the parton level and find the ones with the most sensitivity to each of these anomalous couplings at the LHC.

Search for Anomalous Top-Quark Couplings with the D0 Detector

Anomalous Wtb couplings modify the angular correlations of the top-quark decay products and change the single top-quark production cross section. We present limits on anomalous top-quark couplings by combining information from W boson helicity measurements in top-quark decays and anomalous coupling searches in the single top-quark final state. We set limits on right-handed vector couplings as well as left-handed and right-handed tensor couplings based on about 1 fb(-1) of data collected by the D0 experiment.

T-odd correlations fromCPviolating anomalous top-quark couplings revisited

We revisit the effect of $CP$ violating anomalous top-quark couplings in $t\overline{t}$ production and decay. We consider $t\overline{t}$ production through gluon fusion (and light $q\overline{q}$ annihilation) followed by top-quark decay into $bW$ or $b\ensuremath{\ell}\ensuremath{\nu}$. We find explicit analytic expressions for all the triple products generated by the anomalous couplings that fully incorporate all spin correlations. Our results serve as a starting point for numerical simulations for the CERN LHC.

Optimal-observable analysis of possible new physics using the b-quark in [formula omitted

We study possible anomalous top-quark couplings generated by SU(2)×U(1) gauge-invariant dimension-6 effective operators, using the final b-quark momentum distribution in γγ→tt̄→bX. Taking into account non-standard tt̄γ, tbW and γγH couplings, we perform an optimal-observable analysis in order to estimate the precision for the determination of all relevant non-standard couplings.

Probing anomalous top-quark couplings induced by dim.6 operators at photon colliders

Possible anomalous top-quark couplings induced by SU(2)× U(1) gauge-invariant dimension-6 effective operators were studied in the process of t t ̄ productions and decays at polarized γγ colliders. Two CP-violating asymmetries, a linear-polarization asymmetry and a circular-polarization asymmetry, were computed including both non-standard t t ̄ γ and γγH couplings. An optimal-observable analysis for the process γγ→t t ̄ →l ±⋯ was performed in order to estimate the precision for determination of all relevant non-standard couplings, including the anomalous tbW coupling.

Top-quark spin correlation at linear colliders with anomalous couplings

We investigate the feasibility of probing anomalous top-quark couplings of $Wtb$, $Z t \bar{t}$, and $\gamma t \bar{t}$ in terms of an effective Lagrangian with dimension-six operators at future $e^+e^-$ linear colliders with a c. m. energy $\sqrt s \sim 500-800$ GeV. We first examine the constraints on these anomalous couplings from the $Z\to b \bar{b}$ data at LEP I and from unitarity considerations. We then consider in detail the effects of anomalous couplings on $t \bar{t}$ spin correlations in the top-pair production and decay with three spin bases: the helicity, beamline and off-diagonal bases. Our results show that the polarized beams are more suitable for exploring the effects of different new operators. For polarized beams, the helicity basis yields the best sensitivity.

Probe ofCPviolation ine+e−→tt¯near threshold

We study how to probe the anomalous CP-violating couplings of top quark with photon, Z and gluon in the ttbar threshold region at future e+e- colliders. These couplings contribute to the difference of the t and tbar polarization vectors delta P and to the CP-odd spin correlation tensor delta Q_ij. We find that typical sizes of delta P and delta Q_ij are 5-20% times the couplings (d_tgamma, d_tZ, d_tg) in the threshold region. Experimentally delta P can be measured efficiently using the CP-odd combination of the l+/l- momenta or of the l+/l- directions. We have similar sensitivities to both the real and imaginary parts of the couplings independently using the two components of delta P. Taking advantage of different dependences of delta P on the e+/e- polarizations and on the c.m. energy, we will be able to disentangle the effects of the three couplings d_tgamma, d_tZ, d_tg in the ttbar threshold region. We give rough estimates of sensitivities to the anomalous couplings expected at future e+e- colliders. The sensitivities to d_tgamma and d_tZ are comparable to those attainable in the open-top region at e+e- colliders. The sensitivity to d_tg is worse than that expected at a hadron collider but exceeds the sensitivity in the open-top region at e+e- colliders.

Top-quark decay via the anomalous couplingt¯cγat hadron colliders

We determine the constraints on the anomalous top-quark coupling associated with the flavor-changing neutral current vertex $\bar t c \gamma $ from the limits on the $b$-quark rare decay $b\rightarrow s \gamma$ and non-standard top-quark decays. Based on these constraints, we discuss the experimental observability of the rare decay mode $t \rightarrow c \gamma$, both at the Fermilab Tevatron with a luminosity-upgrade and at the LHC.

Probing nonstandard top-quark couplings using spin correlation

Top spin correlation has been shown to be nontrivial in hadronic top-pair production, and can be realized by the asymmetries of the decay products of the top quark and antiquark. We show in this work that the top spin correlation is a sensitive probe to the anomalous top-quark couplings beyond the standard model. Specifically, we look at the anomalous chromomagnetic and chromoelectric dipole moments, as well as a right-handed component in the weak decay of the top quark. We found a few measurable asymmetries formed by the decay products of the top-quark pair that vary in accord with the spin correlation.