Kazumasa Ohkuma

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

Abstract 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.

Search for anomalous top–gluon couplings at LHC revisited

AbstractThrough top-quark pair productions at LHC, we study possible effects of nonstandard top–gluon couplings yielded by SU(3)×SU(2)×U(1) invariant dimension-6 effective operators. We calculate the total cross section and also some distributions for

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

pp\to t\bar{t}X

Optimal-observable analysis of possible non-standard top-quark couplings in pp→tt¯X→ℓ+X′

as functions of two anomalous-coupling parameters, i.e., the chromoelectric and chromomagnetic moments of the top, which are constrained by the total cross section

Addendum to: Search for anomalous top–gluon couplings at LHC revisited

\sigma(p\bar{p}\to t\bar{t}X)

Latest constraint on nonstandard top-gluon couplings at hadron colliders and its future prospect

measured at Tevatron. We find that LHC might give us some chances to observe sizable effects induced by those new couplings.

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

We study possible anomalous CP-violating Higgs couplings to μ and t 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-observable analysis of possible new physics using the b-quark in γγ→tt̄→bX

Abstract Possible non-standard top-quark interactions with the gluon and the W boson induced by SU ( 3 ) × SU ( 2 ) × U ( 1 ) gauge-invariant dimension-6 effective operators are studied for hadron-collider experiments. Current limits on top-gluon couplings are presented by using the latest experimental data of t t ¯ productions at the Tevatron and the Large Hadron Collider (LHC). The optimal-observable procedure is applied to the charged-lepton distributions in p p → t t ¯ X → l + X ′ ( l = e or μ) at the LHC in order to estimate the expected statistical uncertainties in measurements of those non-standard top-gluon and top-W couplings that contribute to this process in the leading order.

Optimal beam polarizations for new-physics search through γγ→tt̄→ℓX/bX

In our latest paper “Search for anomalous top–gluon couplings at LHC revisited” in Eur. Phys. J. C65 (2010), 127–135 (arXiv:0910.3049 [hep-ph]), we studied possible effects of nonstandard top–gluon couplings through the chromoelectric and chromomagnetic moments of the top quark using the total cross section of

Programming instruction using a micro robot as a teaching tool

p\bar{p}/pp\to t\bar{t}X