Zenro Hioki

Exploring anomalous top-quark interactions via the final lepton in t(t)over-bar productions/decays at hadron colliders

We study momentum distributions of the final-state charged lepton in ppbar/pp --> ttbar --> l^+ X (l=e or mu) at hadron colliders, i.e., Tevatron and Large Hadron Collider (LHC) in order to explore possible new-physics effects in the top-quark sector. Assuming general model-independent ttbar g + ttbar gg and tbW interactions beyond the standard model, we first derive analytical formulas for the corresponding parton-parton processes. We then compute the lepton angular, energy and transverse-momentum distributions in ppbar/pp collisions to clarify how they are affected by those anomalous couplings.

Role of heavy fermions and heavy Higgs scalars in the electroweak correction to the MW − MZ relation

The role of heavy fermions and heavy Higgs-scalars in the MW − MZ relation resulting from the one-loop-corrected μ decay width Γ(1) and its experimental data Γexp is studied in the framework of the standard electroweak theory. Exact and approximate formulae are both given for these heavy particle effects. The quadratic dependence of Γ(1) on large fermion mass mheavy gives a positive contribution to the calculation of MW from Γ(1) = Γexp for a given MZ, and cancels the light fermion contributions of the form ∼ αln(mlight/MW) at the value of mheavy ∼ 200 GeV. On the other hand, the Higgs mass dependence of the calculation is, at best, logarithmic, and does not produce visible effects. Applications for deriving constraints for the top-quark mass (or heavier fermion mass) are discussed, and a concrete example is given of the relation between experimental uncertainties in measurements of MW,Z and the corresponding allowed region for mt.

CP-Violating Lepton-Energy Correlation in e\bar{e}\to t\bar{t}

In order to observe a signal of possible CP violation in top-quark couplings, we have studied energy correlation of the final leptons in

Energy Spectrum of Secondary Leptons in

e^+e^-\to t\bar{t} \to \ell^+\ell^-X / \ell^\pm X

e^+ e^- \to t\bar{t}

at future linear colliders. Applying the recently-proposed optimal method, we have compared the statistical significances of CP-violation-parameter determination using double- and single-lepton distributions. We have found that the single-lepton-distribution analysis is more advantageous.

- Non-standard Interactions and CP Violation -

Abstract The process of top-quark pair production at future high-energy e+e− linear colliders has been investigated as a possible test of physics beyond the Standard Model. Non-standard interactions have been assumed both for the production and for the subsequent decay of the top quarks. The energy spectrum of the single lepton l± and the energy correlation of l+ and l− emerging from the process e + e − → t t → l ± X/l + l − X are calculated. The energy-spectrum asymmetry of l+ and l− is considered as a measure of CP violation. An optimal method to determine whether CP violation occurs in the production or in the decay processes is proposed.

Constraints on generalized nonstandard

General non-standard

tbW

tbW

couplings

couplings are studied as model independently as possible based on the effective Lagrangian consisting of the dimension-6 operators, which is an extension of the standard-model Lagrangian. The

New-Physics Search through gamma gamma -> t tbar -> lX/bX

tbW