Search

The ATLAS collaboration reported excesses at around 2 TeV in the di-boson production decaying into hadronic final states. We consider the possibility of explaining the excesses with extra gauge bosons in two simple non-Abelian extensions of the Standard Model. One is the so-called G(221) models with a symmetry structure of SU(2)1⊗SU(2)2⊗U(1)X and the other is the G(331) models with an extended symmetry of SU(3)C⊗SU(3)L⊗U(1)X. The W' and Z' bosons emerge after the electroweak symmetry is spontaneously broken. Two patterns of symmetry breaking in the G(221) models are considered in this work: one is SU(2)L⊗SU(2)2⊗U(1)X→SU(2)L⊗U(1)Y, the other is SU(2)1⊗SU(2)2⊗U(1)Y→SU(2)L⊗U(1)Y. The symmetry breaking of the G(331) model is SU(3)L⊗U(1)X→SU(2)L⊗U(1)Y. We perform a global analysis of W' and Z' phenomenology in ten new physics models, including all the channels of W'/Z' decay. Our study shows that the leptonic mode and the dijet mode of W'/Z' decays impose a very stringent bound on the parameter space in several new physics models. Such tight bounds provide a useful guide for building new physics models to address on the diboson anomalies. We also note that the Left-Right and Lepton-Phobic models can explain the 3.4σ WZ excess if the 2.6σ deviation in the W+W- pair around 2 TeV were confirmed to be a fluctuation of the SM backgrounds. [ABSTRACT FROM AUTHOR]

Verifying Vtb ≃ 1 is critical to test the three generation assumption of the Standard Model. Sofar our best knowledge of V,b is inferred either from the 3 x 3 unitarity of the Cabibbo-Kobayashi-Maskawa matrix or from single top-quark productions upon the assumption of universal weak couplings. The unitarity could be relaxed in new physics models with extra heavy quarks and the universality of weak couplings could also be broken if the Wtb coupling is modified in new physics models. In this paper we propose to measure Vtb in the process of e+e- → ft without prior knowledge of the number of fermion generations or the strength of the Wtb coupling. Using an effective Lagrangian approach, we perform a model-independent analysis of the interactions among electroweak gauge bosons and the third generation quarks, i.e. the Wtb, Ztt and Zbb couplings. The electroweak symmetry of the Standard Model specifies a pattern of deviations of the Z-tL-tL and W-tL-bL couplings after one imposes the known experimental constraint on the Z-bL-bL coupling. We demonstrate that, making use of the predicted pattern and the accurate measurements of top-quark mass and width from the energy threshold scan experiments, one can determine Vtb from the cross section and the forward-backward asymmetry of top-quark pair production at an unpolarized electron-positron collider. [ABSTRACT FROM AUTHOR]

We propose to utilize the polarization information of the Z bosons in ZZ production, via the gluon-gluon fusion process gg→ZZ, to probe the Ztt gauge coupling. The contribution of longitudinally polarized Z bosons is sensitive to the axial-vector component (at) of the Ztt coupling. We demonstrate that the angular distribution of the charged lepton from Z boson decays serves well for measuring the polarization of Z bosons and the determination of at. We show that ZZ production via the gg→ZZ process complement to Ztt and tZj productions in measuring the Ztt coupling at hadron colliders. [ABSTRACT FROM AUTHOR]

We study the multiple soft gluon radiation effects in Z-boson plus jet production at the LHC. By applying the transverse-momentum-dependent factorization formalism, the large logarithms introduced by the small total transverse momentum of the Z-boson plus leading-jet final-state system are resummed to all orders in the expansion of the strong interaction coupling at the accuracy of the next-to-leading logarithm (NLL). We also compare the prediction of our resummation calculation to the CMS data by employing a reweighting procedure to estimate the effect from imposing kinematic cuts on the leptons from Z-boson decay, and we find good agreement for both the imbalance transverse momentum and the azimuthal angle correlation of the final-state Z-boson and leading-jet system, for pp→Z+jet production at the LHC. [ABSTRACT FROM AUTHOR]

We study the soft gluon radiation effects for the s-channel single top quark production at the LHC. By applying the transverse momentum dependent factorization formalism, the large logarithms about the small total transverse momentum (q⊥) of the single-top plus one-jet final state system are resummed to all orders in the expansion of the strong interaction coupling at the accuracy of next-to-leading Logarithm (NLL). We compare our numerical results with pythia and find that both the q⊥ and ϕ* observables from pythia are consistent with our prediction. Furthermore, we point out that the soft gluon radiation effects from the final state become significant in this process, especially for the boosted kinematical region. [ABSTRACT FROM AUTHOR]

We study the effect of multiple soft gluon radiation on the kinematical distributions of the t-channel single top quark production at the LHC. By applying the transverse momentum-dependent factorization formalism, large logarithms (of the ratio of large invariant mass Q and small total transverse momentum q⊥ of the single-top plus one-jet final state system) are resummed to all orders in the expansion of the strong interaction coupling at the accuracy of the next-to-leading logarithm, including the complete next-to-leading-order corrections. We show that the main difference from PYTHIA prediction lies in the inclusion of the exact color coherence effect between the initial and final states in our resummation calculation, which becomes more important when the final state jet is required to be in the forward region. We further propose to apply the experimental observable ϕ*, similar to the one used in analyzing precision Drell-Yan data, to test the effect of multiple gluon radiation in the single-top events. The effect of the bottom quark mass is also discussed. [ABSTRACT FROM AUTHOR]

We consider effective Higgs boson couplings, including both CP-even and CP-odd couplings, which affect Higgs boson pair production. Through partial wave analysis, we find that the process gg → hh is dominated by the s-wave component even at a 100 TeV pp collider. Making use of s-wave kinematics, we propose a cut efficiency function to mimic the collider simulation and obtain the potential of measuring Higgs effective couplings at the 14 TeV LHC with an integrated luminosity of 3000 fb-1 and at a 100 TeV pp collider. Analytical expressions of 2σ exclusion limits at the LHC and 5 σ discovery bands at the 100 TeV machine are given. [ABSTRACT FROM AUTHOR]

Determination of trilinear Higgs coupling (λHHH=κλSMHHH) through Higgs pair productions is a major motivation for the LHC high-luminosity phase. We perform a detailed collider simulation to explore the potential of measuring λHHH in the VHH (V=W, Z) production at the high-luminosity Large Hadron Collider. We find that the trilinear Higgs coupling in the standard model (λSMHHH) can be measured at the level of 1.3σ. Combining with the gluon fusion, vector boson fusion, and ttHH channels, λSMHHH is expected to be measured at the level of 3.13σ. If no evidence of Higgs pair productions is observed, the VHH production, together with the gluon fusion channel, imposes a bound of 0.5≤κ≤2.2 at the 95% confidence level. [ABSTRACT FROM AUTHOR]

We study double parton scattering (DPS) processes involving electroweak gauge bosons at the 13 and 100 TeV proton-proton colliders. Specifically, we focus on three DPS channels: W-boson plus two jets (W⊗jj), Z-boson plus two jets (Z⊗jj), and same-sign W pair production (W±⊗W±). We demonstrate that the Z⊗jj process, which has not received much attention, is the best channel for measuring the effective cross section σeff. The accuracy of the σeff measurement in the three DPS channels, especially the W±⊗W± production, is significantly improved at the 100 TeV colliders. We advocate that combined analysis of the three DPS channels could test the universality of the effective cross section σeff. [ABSTRACT FROM AUTHOR]