arXiv subjects

M. Jeżabek

Publications and source records attributed to M. Jeżabek.

11 recordsLinked to original sources

arXiv1994

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.

hep-ph↗

arXiv1994

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.

hep-ph↗

arXiv1994

Radiation of Heavy Quarks

The rate for the production of massive fermions radiated off a pair of massless fermions is calculated analytically. Combined with the analytic calculation of the corresponding virtual contribution one obtains the order $α^2$ correction to the cross section which is induced by the real and virtual radiation of a pair of massive fermions by massless fermions. Approximations valid for large and for small masses are derived and shown to agree with earlier calculations.

hep-ph↗

arXiv1994

Top Quark Physics

Top quark studies at future $e^+e^-$ colliders are considered. Two issues are discussed: {a --}Some results are presented on the decays of top quarks. Energy distributions of charged leptons and neutrinos in $t\to bW\to be^+ν$ and jets in $t\to bW\to b\bar du$ decays are sensitive to the structure of $tbW$ vertex. Distributions of charged leptons from top decays are particularly useful in polarization studies whereas neutrinos are sensitive to deviations from the Standard Model. {b --}Recent calculations are reviewed on the top quark pair production in $e^+e^-$ annihilation. The differential cross sections in the threshold region can lead to an accurate determination of the top quark mass and the interquark potential. The effects of the top-Higgs Yukawa coupling and some higher order QCD corrections are also under control.

hep-ph↗

arXiv1994

Hadron Radiation in Leptonic $Z$ Decays

The rate for the final state radiation of hadrons in leptonic $Z$ decays is evaluated, using as input experimental data for $σ(e^+e^-\to hadrons)$ in the low energy region. Configurations with a lepton pair of large and a hadronic state of low invariant mass are dominant. A relative rate $Γ_{l\bar l had}/Γ_{l\bar l}=6.3\times 10^{-4}$ is calculated. This result is about twice the prediction based on a parton model calculation with a quark mass of $300$ MeV. The rate for secondary production of heavy quarks is calculated in the same formalism.

hep-ph↗

arXiv1994

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.

hep-ph↗

arXiv1994

Distributions of leptons in decays of polarised heavy quarks

Analytic formulae are given for QCD corrections to the lepton spectra in decays of polarised up and down type heavy quarks. These formulae are much simpler than the published ones for the corrections to the spectra of charged leptons originating from the decays of unpolarised quarks and polarised up type quarks. Distributions of leptons in semileptonic $Λ_c$ and $Λ_b$ decays can be used as spin analysers for the corresponding heavy quarks. Thus our results can be applied to the decays of polarised charm and bottom quarks. For the charged leptons the corrections to the asymmetries are found to be small in charm decays whereas for bottom decays they exhibit a non-trivial dependence on the energy of the charged lepton. Short life-time enables polarisation studies for the top quark. Our results are directly applicable for processes involving polarised top quarks.

hep-ph↗

arXiv1993

QCD corrections to decays of polarised charm and bottom quarks

Distributions of charged leptons in semileptonic $Λ_c$ and $Λ_b$ decays can be used as spin analysers for the corresponding charm and bottom quarks. QCD corrections to the energy spectra of charged leptons have been given in the literature as well as the corrections to the angular dependence for polarised up-type quarks. The analogous formulae are derived also for polarised down-type quarks. These results are applied to the decays of polarised charm and bottom quarks. The corrections to the asymmetries are found to be small for charm decays. For bottom decays they exhibit a non-trivial dependence on the energy of the charged lepton.

hep-ph↗

arXiv1993

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.

hep-ph↗

arXiv1993

Energy of W distribution in top quark decays

A relatively simple analytical formula is derived for the energy spectrum of $W$ boson in top quark decays $t\to Wb$ including ${\cal O}(α_s)$ radiative corrections. We discuss the accuracy of this formula and compare it to a more general albeit more complicated one derived in \cite{CJK}~. A Monte Carlo algorithm for generation of $W$ energy spectrum is briefly described.

hep-ph↗

arXiv1993

The Top Width - Theoretical update

A critical assessment of the available calculations of the top quark width is presented. QCD corrections, the finite mass of the $b$ quark and the effect of the $W$ width are included as well as the electroweak corrections. The relative importance of these corrections is demonstrated for the realistic range of top masses. For the QCD corrected decay rate we use the formulae from \cite{JK1} and include the electroweak correction taken from \cite{DS}. Our results differ from those available in the literature because all the later calculations ignored the effect of W width discussed earlier in \cite{JK1}~. This leads to an effect comparable in size to the electroweak correction.

hep-ph↗