Tau-jet signatures of vectorlike quark decays to heavy charged and neutral Higgs bosons

We study 4b + 2τ and 4b + 1τ signatures of heavy neutral and charged Higgs bosons originating from cascade decays of pair-produced new quarks. Decays of vectorlike quarks through heavy Higgses can easily dominate in the two Higgs doublet model of type-II, and the studied signatures are common to many possible decay chains. We design search strategies for these final states and discuss the mass ranges of heavy Higgs bosons and new quarks that can be explored at the Large Hadron Collider as functions of branching ratios in a model independent way. We further combine the results with a similar study focusing on decays which lead to a 6b final state and interpret the sensitivity to charged and neutral Higgs bosons and vectorlike quarks in the type-II two Higgs doublet model. We find that the LHC reach for their masses extends to well above 2 TeV in the case of an SU(2) doublet quark and to at least 1.8 TeV for a bottom-like SU(2) singlet quark in the whole range of tan β between 1 and 50.

Constraining CP4 3HDM with Top Quark Decays

CP4 3HDM is a unique three-Higgs-doublet model equipped with a higher-order CP-symmetry in the scalar and Yukawa sector. Based on a single assumption (the minimal model with a CP-symmetry of order 4 and no accidental symmetry), it leads to a remarkable correlation between its scalar and Yukawa sectors, which echoes in its phenomenology. A recent scan of the parameter space of CP4 3HDM under the assumption of scalar alignment identified a few dozens of points which passed many flavor constraints. In the present work, however, we show that almost all of these points are now ruled out by the recent LHC searches of t→H+b with subsequent hadronic decays of H+. Apart from a few points with charged Higgses heavier than the top quark, only one point survives all the checks, the model with an exotic, non-2HDM-like generation pattern of H+ couplings with quarks. One can expect many more points with exotic H+ couplings to quarks if the scalar alignment assumption is relaxed.

Erratum to: The electro-weak couplings of the top and bottom quarks — global fit and future prospects

In the course of follow-up work a mistake was discovered in the parameterization of the dependence of the W-boson helicity fractions in top quark decays. The dependence on two operator coefficients, Cφtb and CbW, was erroneously omitted. Inclusion of this dependence leads to significantly stronger bounds on these operators from the current data and modifies also the HL-LHC prospects. The expectations for e+e− colliders are not affected. We present corrected results in this erratum.

Completing 1/$$ {m}_b^3 $$ corrections to non-leptonic bottom-to-up-quark decays

We compute the contributions of dimension six two-quark operators to the non-leptonic decay width of heavy hadrons due to the flavor changing bottom-to-up-quark transition in the heavy quark expansion. Analytical expressions for the Darwin term ρD and the spin-orbit term ρLS are obtained with leading order accuracy.

Combination of the W boson polarization measurements in top quark decays using ATLAS and CMS data at $$ \sqrt{s} $$ = 8 TeV

The combination of measurements of the W boson polarization in top quark decays performed by the ATLAS and CMS collaborations is presented. The measurements are based on proton-proton collision data produced at the LHC at a centre-of-mass energy of 8 TeV, and corresponding to an integrated luminosity of about 20 fb−1 for each experiment. The measurements used events containing one lepton and having different jet multiplicities in the final state. The results are quoted as fractions of W bosons with longitudinal (F0), left-handed (FL), or right-handed (FR) polarizations. The resulting combined measurements of the polarization fractions are F0 = 0.693 ± 0.014 and FL = 0.315 ± 0.011. The fraction FR is calculated from the unitarity constraint to be FR = −0.008 ± 0.007. These results are in agreement with the standard model predictions at next-to-next-to-leading order in perturbative quantum chromodynamics and represent an improvement in precision of 25 (29)% for F0 (FL) with respect to the most precise single measurement. A limit on anomalous right-handed vector (VR), and left- and right-handed tensor (gL, gR) tWb couplings is set while fixing all others to their standard model values. The allowed regions are [−0.11, 0.16] for VR, [−0.08, 0.05] for gL, and [−0.04, 0.02] for gR, at 95% confidence level. Limits on the corresponding Wilson coefficients are also derived.

Rare decays of the top quark mediated by Z′ gauge bosons and flavor violation

The rare top quark decays mediated by a new neutral massive gauge boson that is predicted in models with extended gauge symmetries are studied. We focus on the processes [Formula: see text] induced at the one loop level, where [Formula: see text], by considering different extended models. It is found that, within a broad range of mass of the new neutral gauge boson, the models predict branching ratios for the decays in study that are competitive with respect to the corresponding branching ratios in the Standard Model (SM). In order to establish bound on our branching ratios, we consider the recent experimental bounds as [Formula: see text], depending on the model, which also impose restrictions on our calculation. Even in this case, the resulting branching ratios are of the same order of magnitude as that predicted by the SM. It should be noted that for the case of two models studied here, since no experimental bound exists to compare with, the results could be important, as they are, in the best of cases, two orders of magnitude larger than the predicted by the SM.

Parton showers and matching uncertainties in top quark pair production with Herwig 7

We evaluate the theoretical uncertainties in next-to-leading order plus parton shower predictions for top quark pair production and decay in hadronic collisions. Our work is carried out using the Herwig 7 event generator and presents an in-depth study of variations in matching schemes with two systematically different shower algorithms, the traditional angular-ordered and alternative dipole shower. We also present all of the required extensions of the Herwig dipole shower algorithm to properly take into account quark mass effects, as well as its ability to perform top quark decays. The predictions are compared at parton level as well as to Large Hadron Collider data, including in the boosted regime. We find that the regions where predictions with a non-top-quark-specific tune differ drastically from data are plagued by large uncertainties which are consistent between our two shower and matching algorithms.