Polarization in Top Quark Pair Production near Threshold

The polarization dependent momentum distributions of top quarks and their decay products are calculated for $t\bar t$ production at future $e^+e^-$ colliders with polarized beams. The Green function formalism is applied to this reaction near energy threshold. The Lippmann--Schwinger equations for the $S$-wave and $P$-wave Green functions are solved numerically for the QCD chromostatic potential given by the two-loop formula at large momentum transfers and Richardson ansatz at intermediate and small ones. It is demonstrated that for the longitudinally polarized electron beam an optimally polarized sample of top quarks can be produced.Comment: 11 pages, LaTex (uses epsf.sty, 3 ps-figures appended as extra uuencoded file). The complete paper, including figures, is also available via anonymous ftp at ftp://ttpux2.physik.uni-karlsruhe.de/ttp94-28/ttp94-28.ps, or via www at http://ttpux2.physik.uni-karlsruhe.de/preprints.htm

Momentum Distributions in ttˉt\bar t

We apply the Green function formalism for $t-\bar t$ production and decay near threshold in a study of the effects due to the momentum dependent width for such a system. We point out that these effects are likely to be much smaller than expected from the reduction of the available phase space. The Lippmann--Schwinger equation for the QCD chromostatic potential is solved numerically for $S$ partial wave. We compare the results on the total cross section, top quark intrinsic momentum distributions and on the energy spectra of $W$ bosons from top quark decays with those obtained for the constant width.Comment: 12 pages (without figures) (11 (sub)figures available on request), Karlsruhe preprint TTP93-11, hep-ph/yymmnn

Final-State Interactions in e^+e^- -> t\bar{t} -> b l^+ \nu \bar{b} W^- Near Top Quark Threshold

We calculate final-state interaction corrections to the energy-angular distribution of l^+ in semi-leptonic top quark decay, where the parent top quark is produced via e^+e^- -> t\bar{t} near threshold. These are the corrections due to gluon exchange between t and \bar{b} (\bar{t} and b) and between b and \bar{b}. Combining with previously known other corrections, we explicitly write down the l^+ energy-angular distribution including the full O(alpha_s)=O(beta) corrections near t\bar{t} threshold. Numerical analyses of the final-state interaction corrections are given. We find that they deform the l^+ distribution typically at the 10% level. We also find that all qualitative features of the numerical results can be understood from intuitive pictures. The mechanisms of various effects of the final-state interactions are elucidated. Finally we define an observable which is proper to the decay process of the top quark (dependent only on d\Gamma_{t -> b l^+ \nu}/ dE_l d\Omega_l of a free polarized top quark) near t\bar{t} threshold. Such a quantity will be useful in extracting the decay property of the top quark using the highly polarized top quark samples.Comment: Section 6 is enlarged substantially and a paragraph is added to Section 8 correspondingly. Reference list is also improved. (27 pages including figures, LaTeX

Comment on the Average Momentum of Top Quarks in the Threshold Region

The behavior of the momentum distribution of top quarks in the threshold region is investigated. The qualitative behavior, in particular the dependence of the average momentum on the strong coupling constant can be understood from analytical calculations for the Coulomb potential. Ambiguities in the relation between the excitation curve and the top mass are addressed.Comment: Univ. of Karlsruhe preprint TTP93-31, LaTeX, 6 pages including two figures (uses epsf) appended as uuencoded postscript fil

Neutrino Masses and Bimaximal Mixing

Solar and atmospheric neutrino anomalies are described by bimaximal mixing of three neutrinos. Neutrino oscillations in appearance nu_e nu_mu,nu_tau and in disappearance nu_e long baseline and atmospheric experiments are sensitive to deviations from the ideal bimaximal mixing. It is suggested that these deviations may be dominated by a rotation in the electron--muon plane of the generation space. Simple seesaw models are described supporting this idea. The rotation angle is estimated from Fritzsch's relation. Predictions are presented for oscillations in long baseline experiments, for solar neutrinos, and for the rates of neutrinoless double beta decays.Comment: Latex, 13 p., no figure

Gluon interference effects in t-tbar production at the Next Linear Collider

We study the effects of gluon interference in the production and semi-leptonic decay of a t-tbar pair above threshold at the Next Linear Collider (NLC). We calculate all matrix elements to next-to-leading order and use the resulting expressions for the development of a Monte Carlo event generator. Our results show effects at the level of 10% in differential cross-sections. We thus extend previous results obtained by analytical means in the soft-gluon limit.Comment: 20 pages, incl. 9 figures, LaTeX (revtex, eepic, axodraw

V-a Tests Through Leptons from Polarised Top Quarks

Angular-energy distributions are studied for charged leptons and neutrinos from the decays of polarised top quarks. A small admixture of V+A interactions is incorporated. The polarisation dependent part of the neutrino distribution which can be measured experimentally through the missing momentum is particularly sensitive towards deviations from the V-A structure. This result remains unaffected by QCD corrections which, however, cannot be neglected in a quantitative analysis.Comment: 10 pages, LaTex (uses epsf.sty, 2 figures appended as uuencoded ps files). A complete postscript file, including figures, is available via anonymous ftp at ttpux2.physik.uni-karlsruhe.de (129.13.102.139) as /ttp94-4/ttp94-4.ps, Local preprint# TTP94-

Polarization in Top Quark Production and Decay near Threshold

Theoretical results are presented for top quarks produced in annihilation of polarized electrons on positrons. Polarization studies for $t\bar t$ pairs near threshold are free from hadronization ambiguities. This is due to the short lifetime of the top quark. Semileptonic decays are discussed as well as their applications in studying polarization dependent processes involving top quarks. The Green function formalism is applied to $t\bar t$ production at future $e^+e^-$ colliders with polarized beams. Lippmann--Schwinger equation is solved numerically for the QCD chromostatic potential given by the two-loop formula at large momentum transfers and Richardson ansatz at intermediate and small ones. The polarization dependent momentum distributions of top quarks and their decay products are calculated.Comment: 6 pages, LaTex (uses epsf.sty, 2 figures appended as uuencoded ps files). The complete paper, including figures, is also available via anonymous ftp at ttpux2.physik.uni-karlsruhe.de (129.13.102.139) as /ttp94-24/ttp94-24.ps, or via www at http://ttpux2.physik.uni-karlsruhe.de/preprints.html

Glueballs in the bag models

The influence of the bag shape on the lowest lying gluonium states is investigated. The MIT and the surface tension version of the bag model are considered