Probe of CP Violation in e+e- -> ttbar Near Threshold

We study how to probe the anomalous CP-violating couplings of top quark with photon, Z and gluon in the ttbar threshold region at future e+e- colliders. These couplings contribute to the difference of the t and tbar polarization vectors delta P and to the CP-odd spin correlation tensor delta Q_ij. We find that typical sizes of delta P and delta Q_ij are 5-20% times the couplings (d_tgamma, d_tZ, d_tg) in the threshold region. Experimentally delta P can be measured efficiently using the CP-odd combination of the l+/l- momenta or of the l+/l- directions. We have similar sensitivities to both the real and imaginary parts of the couplings independently using the two components of delta P. Taking advantage of different dependences of delta P on the e+/e- polarizations and on the c.m. energy, we will be able to disentangle the effects of the three couplings d_tgamma, d_tZ, d_tg in the ttbar threshold region. We give rough estimates of sensitivities to the anomalous couplings expected at future e+e- colliders. The sensitivities to d_tgamma and d_tZ are comparable to those attainable in the open-top region at e+e- colliders. The sensitivity to d_tg is worse than that expected at a hadron collider but exceeds the sensitivity in the open-top region at e+e- colliders.Comment: 25 pages, 9 figure

Singe Top Production at LEP 200

We present exact tree level cross sections for the single top production process $e^- e^+ \rightarrow e^- \bar{\nu}_e t \bar{b}$ at LEP~200. The results reproduce roughly those obtained earlier by using the equivalent real photon approximation and we confirm the observation that detecting a top heavier than half the c.m.~energy is not feasible at LEP~200. The calculation has been performed by a new automatic Feynman amplitude generator MadGraph which produces HELAS code for the helicity amplitudes.Comment: 7 pages, 4 postscript figure

Precision W-boson and top-quark mass determinations at a muon collider

Precise determinations of the masses of the $W$ boson and of the top quark could stringently test the radiative structure of the Standard Model (SM) or provide evidence for new physics. We analyze the excellent prospects at a muon collider for measuring $M_W$ and $m_t$ in the $W^+W^-$ and $t\bar t$ threshold regions. With an integrated luminosity of 10 (100) fb$^{-1}$, the $W$-boson mass could be measured to a precision of 20 (6) MeV, and the top-quark mass to a precision of 200 (70) MeV, provided that theoretical and experimental systematics are understood. A measurement of $\Delta m_t=200$ MeV for fixed $M_W$ would constrain a 100 GeV SM Higgs mass within about $\pm 2$ GeV, while $\Delta M_W=6$ MeV for fixed $m_t$ would constrain $m_h$ to about $\pm 10$ GeV.Comment: 27 pages, 11 figures, postscript file available via anonymous ftp://ucdhep.ucdavis.edu/han/mumu/mwmt.p

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