5,476 research outputs found
Determining at Electron-Positron Colliders
Verifying is critical to test the three generation
assumption of the Standard Model. So far our best knowledge of is
inferred either from the unitarity of CKM 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 coupling
is modified in new physics models. In this work we propose to measure
in the process of without prior knowledge of the number
of fermion generations or the strength of the 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 , and couplings. The electroweak symmetry
of the Standard Model specifies a pattern of deviations of the --
and -- couplings after one imposes the known experimental
constraint on the -- 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 from the
cross section and the forward-backward asymmetry of top-quark pair production
at an {\it unpolarized} electron-positron collider.Comment: publish versio
Combined Effect of QCD Resummation and QED Radiative Correction to W boson Observables at the Tevatron
A precise determination of the W boson mass at the Fermilab Tevatron requires
a theoretical calculation in which the effects of the initial-state multiple
soft-gluon emission and the final-state photonic correction are simultaneously
included . Here, we present such a calculation and discuss its prediction on
the transverse mass distribution of the W boson and the transverse momentum
distribution of its decay charged lepton, which are the most relevant
observables for measuring the W boson mass at hadron colliders.Comment: 10 pages, 3 Postscript figures, uses revtex4.st
Signatures of Extra Gauge Bosons in the Littlest Higgs Model with T-parity at Future Colliders
We study the collider signatures of a T-odd gauge boson pair
production in the Littlest Higgs Model with T-parity (LHT) at Large Hadron
Collider (LHC) and Linear Collider (LC). At the LHC, we search for the
boson using its leptonic decay, i.e. , which
gives rise to a collider signature of \ell^{+}\ell^{\prime-}+\met. We
demonstrate that the LHC not only has a great potential of discovering the
boson in this channel, but also can probe enormous parameter space of
the LHT. Due to four missing particles in the final state, one cannot
reconstruct the mass of at the LHC. But such a mass measurement can be
easily achieved at the LC in the process of . We present an
algorithm of measuring the mass and spin of the boson at the LC.
Furthermore, we illustrate that the spin correlation between the boson and
its mother particle () can be used to distinguish the LHT from other new
physics models.Comment: version to appear in PRD (a few references added
Next-to-Leading Order Corrections to Single Top Quark Production and Decay at the Tevatron: 1. s-channel Process
We present a study of s-channel single top quark production at the upgraded
Tevatron collider, including the next-to-leading order (NLO) QCD
corrections to the production and the decay of the top quark. The "modified"
narrow width approximation was adopted to preserve the spin of the top quark in
its production and decay. We discuss the effect of the different
contributions on the inclusive cross section as well as various kinematic
distributions after imposing the relevant cuts to select s-channel single top
signal events. In particular the decay contribution, while small
in size, has a significant impact on several distributions. With the help of
the best-jet algorithm to reconstruct the top quark we demonstrate that it is
possible to study kinematical and spin correlations in s-channel single top
events. We furthermore compare top quark spin measurements in two different
basis and show how NLO corrections have to be taken into consideration in
searches for the Higgs boson through associated production at the
Tevatron.Comment: 39 pages, 37 figure
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