arXiv subjects
Publications and source records attributed to A. Kadeer.
We provide a pedagogical introduction to the subject of Standard Model decays of unpolarized top quarks into unpolarized and polarized $W$-bosons including their QCD and electroweak radiative corrections.
Using the helicity method we derive complete formulas for the joint angular decay distributions occurring in semileptonic hyperon decays including lepton mass and polarization effects. Compared to the traditional covariant calculation the helicity method allows one to organize the calculation of the angular decay distributions in a very compact and efficient way. In the helicity method the angular analysis is of cascade type, i.e. each decay in the decay chain is analyzed in the respective rest system of that particle. Such an approach is ideally suited as input for a Monte Carlo event generation program. As a specific example we take the decay $Ξ^0 \to Σ^+ + l^- + \barν_l$ ($l^-=e^-, μ^-$) followed by the nonleptonic decay $Σ^+ \to p + π^0$ for which we show a few examples of decay distributions which are generated from a Monte Carlo program based on the formulas presented in this paper. All the results of this paper are also applicable to the semileptonic and nonleptonic decays of ground state charm and bottom baryons, and to the decays of the top quark.
The azimuthal correlation between the planes formed by the vectors $(\vec{p}_\ell,\vec{p}_{X_b})$ and $(\vec{p}_\ell,\vec{P}_t)$ in the semileptonic rest frame decay of a polarized top quark $t(\uparrow) \to X_b + l^+ + ν_\ell$ belongs to a class of polarization observables involving the top quark which vanish at the Born term level in the standard model. We determine the next--to--leading order QCD corrections to the afore-mentioned azimuthal correlation and compare the result to the corresponding contribution of a non--standard--model right--chiral quark current.
We calculate the $ O(α_s) $ radiative corrections to polarized top quark decay into a charged Higgs boson and a massive bottom quark in two variants of the two-Higgs-doublet model. The radiative corrections to the polarization asymmetry of the decay may become as large as $ 25 % $. We provide analytical formulae for the unpolarized and polarized rates for $ m_b \neq 0 $ and for $ m_b = 0 $. For $ m_b = 0 $ our closed-form expressions for the unpolarized and polarized rates become rather compact.