Optimal-observable Analysis Research Articles

Top-quark electroweak couplings at the FCC-ee

An optimal-observable analysis of the lepton angular and energy distributions from top-quark pair production with semi-leptonic decays in e+e− collisions is used to predict the potential sensitivity of the FCC-ee to the couplings of the top quark to the photon and the Z.

Probing non-standard top-quark couplings via optimal-observable analyses at LHC

Focusing attention on top-quark pair production and its decay processes at the LHC, non-standard top-quark couplings are studied based on the effective Lagrangian constructed with SU(3)X SU(2)X U(1) invariant dimension-6 operators. The optimal-observable analysis is carried out for the charged-lepton distributions in pp -> t t-bar X -> l^+ X' (l=e or mu) in order to estimate the expected statistical uncertainties in measurements of those non-standard t t-bar g and tbW couplings that contribute to this process in the leading order.

Studying possible CP-violating Higgs couplings through top-quark pair productions at muon colliders

We study possible anomalous CP-violating Higgs couplings to mu mu-bar and t t-bar fully model-independent way through top-quark pair productions at muon colliders. Assuming additional non-standard neutral Higgs bosons, whose couplings with top-quark and muon are expressed in the most general covariant form, we carry out analyses of effects which they are expected to produce via CP-violating asymmetries and also the optimal-observable (OO) procedure under longitudinal and transverse muon polarizations. We find the measurement of the asymmetry for longitudinal beam polarization could be useful to catch some signal of CP violation, and an OO analysis might also be useful if we could reduce the number of unknown parameters with a help of other experiments and if the size of the parameters is at least O(1) ~ O(10).

Optimal beam polarizations for new-physics search throughγγ→tbar t→ellX/bX

We perform an optimal-observable analysis of the final charged-lepton/b-quark momentum distributions in gamma+gamma -> t+tbar -> lX/bX for various beam polarizations in order to study possible anomalous t-tbar-gamma, tbW and gamma-gamma-H couplings, which could be generated by SU(2)xU(1) gauge-invariant dimension-6 effective operators. We find optimal beam polarizations that will minimize the uncertainty in determination of those non-standard couplings. We also compare e+ebar and gamma+gamma colliders from the viewpoint of the anomalous-top-quark-coupling determination.

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.

Effects of top-quark anomalous decay couplings at γγ colliders

Most general tbW couplings were investigated in the process γγ → t t → l ± X for unpolarized photon beams. The double angular and energy distribution of the lepton was calculated and an optimal-observable analysis on it was carried out for the SM t t production mechanism. It was also shown that the leptonic angular distribution is insensitive to non-standard tbW vertex. That means that observation of non-standard effects indicates existence of some new physics in the production part.

Optimal-observable analysis of the angular and energy distributions for top-quark decay products at polarized linear colliders

An optimal-observable analysis of the angular and energy distributions of the leptons and bottom quarks in the process e+e−→tt̄→l±/(−)b⋯ has been performed in order to measure the most general top-quark couplings to gauge bosons at polarized linear colliders. The optimal beam polarization for determination of each coupling has been found. A very sensitive test of CP violation in tt̄ production and decay has been proposed.