Bing-Lin Young

Direct top quark production at hadron colliders as a probe of new physics

We examine the effect of an anomalous flavor-changing chromomagnetic moment which allows direct top quark production (two partons combining into an unaccompanied single top quark in the s channel) at hadron colliders. We consider both t-c-g and t-u-g couplings. We find that the anomalous charm quark coupling parameter {kappa}{sub c}/{Lambda} can be measured down to 0.06TeV{sup {minus}1}(0.009TeV{sup {minus}1}) at the Fermilab Tevatron with the Main Injector upgrade (CERN LHC). The anomalous up quark coupling parameter {kappa}{sub u}/{Lambda} can be measured to 0.02TeV{sup {minus}1}(0.003TeV{sup {minus}1}) at the Tevatron (LHC). {copyright} {ital 1997} {ital The American Physical Society}

Searching for t → cg at the Fermilab Tevatron

Abstract We examine the experimental observability of the decay mode t → cg at the Fermilab Tevatron via the flavor-changing neutral current vertex t c g . We find that with the existing data, one should be able to probe the t c g coupling to a value smaller than indirect limits previously obtained from b → sγ and the measured branching fraction for t → bW, reaching BF(t → cg) ∼ 15%–28%. A data sample of 1 fb−1 (10 fb−1) at s =2 Te may probe the t → cg branching fraction to a level of 2% (0.5%).

Top-quark decay via the anomalous coupling {bar t}c{gamma} at hadron colliders

We determine the constraints on the anomalous top-quark coupling associated with the flavor-changing neutral current vertex {bar t}c{gamma} from the limits on the b-quark rare decay b{r_arrow}s{gamma} and nonstandard top-quark decays. Based on these constraints, we discuss the experimental observability of the rare decay mode t{r_arrow}c{gamma}, both at the Fermilab Tevatron with a luminosity upgrade and at the CERN LHC. {copyright} {ital 1997} {ital The American Physical Society}

Phenomenology of a nonstandard top quark Yukawa coupling.

There are theoretical speculations that the top quark may have different properties from that predicted by the standard model. We use an effective Lagrangian technique to model such a nonstandard top quark scenario. We parametrize the [ital CP]-violating interactions of the top quark with the bubble wall in terms of an effective top quark Yukawa coupling, then study its effects on electroweak baryogenesis. We also discuss the phenomenology of such an effective Yukawa coupling in low and high energy regions.

Implications of a non-standard light Higgs boson

Abstract Analyses of the vacuum stability of the electroweak theory indicate that new physics occur at a scale of the order of 1 TeV if a light Higgs is discovered at LEP II. In this paper, we parameterize the effects of new physics in the effective Lagrangian approach and examine its implication on the Higgs boson production at LEP II. We consider the effect of a higher dimension operator on the Higgs potential and calculate the lower bound on the Higgs boson mass from the requirement of vacuum stability. We show that if a Higgs boson is seen at LEP II, then under favourable conditions the deviation of the production cross section from the standard model value could be significant and therefore the presence of the new physics is detectalbe at LEP II.

Realistic Earth matter density for CP violation in a very long baseline neutrino oscillation

We examine the effect of a more realistic Earth matter density model which takes into account of the local density variations along the baseline of a possi ble 2100 km very long baseline neutrino oscillation experiment. Its influence to the measurement of CP violation is investigated and a comparison with the commonly used global density models made. Significant differences are found in the comparison of the results of the different density models.

Searching for an anomalous coupling via single top quark production at a γγ collider

Abstract We investigate the potential of a high-energy γγ collider to detect an anomalous t qγ coupling from observation of the reaction γγ→t q , t q , where q=c or u. We find that with b-tagging and suitable kinematic cuts this process should be observable if the anomalous coupling κ/Λ is no less than about 0.05/TeV, where Λ is the scale of new physics associated with the anomalous interaction. This improves upon the bound possible from observation of top decays at the Tevatron.

Nonuniversal correction to {ital Z}{r_arrow}{ital b{bar b}} and flavor-changing neutral current couplings

A non-universal interaction, which involes only the heavy quarks (tL, bL) and tR, modifies the neutral current couplings and induces flavor changing neutral currents (FCNC). The size of the FCNC effect depends crucially on the dynamics of the fermion mass generation. In this paper, we study the effect of the nonuniversal interaction on Zbb, Zbs, Zds and Zdb, by using an effective lagrangian technique and assuming the quark mass matrices in the form of a generalized Fritzsch ansatz. We point out that if fitting Rb = ( Z → bb)/( Z → Hadrons) to the LEP data within 1 σ, the induced FCNC couplings are very close to the allowed bounds of several rare decays.

Testing Electroweak Models With Polarized Moller Scattering

Abstract Moller scattering (e−e− → e−e−) at the Single Loop Collider (SLC) at SLAC with longitudinally polarized beams provides an easy method for distinguishing among electroweak models. We show that Moller scattering can easily distinguish the standard model from a recently proposed left-right symmetric model with a low right-handed mass scale.

Top quark at the upgraded Tevatron to prove new physics

This talk is a review of the recent studies on probing new physics through single top quark processes and probing exotic top quark decays at the upgraded Tevatron.