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K. Kolodziej

Publications and source records attributed to K. Kolodziej.

13 recordsLinked to original sources
arXiv2013

Anomalous Wtb coupling at the LHC

Some distributions of the mu- in the top quark pair production reaction pp -> b u anti-d anti-b mu- anti-nu_mu at the LHC are calculated to leading order in the presence of the anomalous Wtb coupling with operators of dimension up to five. The distributions in the transverse momentum, rapidity and cosine of the mu- angle with respect to the beam in the laboratory frame and with respect to the reversed momentum of the b-quark in the rest frame of W-boson are changed rather moderately by the anomalous Wtb coupling. The distributions computed with the full set of leading order Feynman diagrams practically do not differ from those computed with the t anti-t production diagrams, with typical acceptance cuts. This demonstrates very little effect of the off resonance background contributions.

hep-ph↗
arXiv2012

New developments in CARLOMAT

New developments in CARLOMAT, a program for automatic computation of the lowest order cross sections, are presented. They include improvements of the phase integration routines and implementation of extensions of the standard model, such as scalar electrodynamics or the anomalous Wtb coupling including operators of dimension up to five.

hep-ph↗
arXiv2012

Anomalous Wtb coupling and forward-backward asymmetry of top quark production at the Tevatron

An influence of the anomalous Wtb coupling on forward-backward asymmetry of top quark pair production at the Tevatron is investigated taking into account decays of the top quarks to 6 fermion final states containing one charged lepton. To this end the most general effective Lagrangian of the Wtb interaction containing terms of dimension up to five is implemented into 'carlomat', a general purpose Monte Carlo program, which allows to compute automatically all necessary cross sections in the presence of anomalous vector and tensor form factors. A sample of results which illustrate little effect of the left- and right-handed tensor form factors on the t\bar t invariant mass dependent forward-backward asymmetry and the charge-signed rapidity distribution of the lepton originating from the W boson from top quark decay is shown.

hep-ph↗
arXiv2003

An anomalous Wtb coupling at a linear collider

Differential cross sections of secondary particles in a process of top quark pair production and decay into six fermions at a linear collider with an unpolarized and a longitudinally polarized electron beam are computed to the lowest order in the standard model and in the presence of an anomalous Wtb coupling. It is illustrated that the latter has a little impact on the differential cross sections. In particular, it is shown that the angular distribution of a secondary lepton receives practically no contribution from the anomalous Wtb coupling, even if the top quark is produced off shell and the non-double resonance background contributions are taken into account. This finding is in accordance with the decoupling theorem that has been proven in literature in the narrow top quark width approximation.

hep-ph↗
arXiv2002

Results for all reactions e+ e- -> 4f, 4f + gamma with nonzero fermion masses

We accomplish our efforts to obtain predictions for all four-fermion final states of e+ e- annihilation and the corresponding bremsstrahlung reactions which are possible in the framework of the Standard Model. For this purpose we have developed a program EE4FGAMMA. Our predictions are valid for fermions of arbitrary masses and we can obtain results for total cross sections without any collinear cut. Keeping exact fermion masses is of course required for top quark production. We give a detailed phenomenological analysis of fermion mass effects and real photon radiation for all channels of four-fermion production at LEP-II and next linear collider energies.

hep-ph↗
arXiv2000

Fermion mass effects in e+e- --> 4f and e+e- --> 4f gamma with cuts

The fermion mass effects in e+ e- --> 4f and in the corresponding bremsstrahlung reactions in the presence of realistic cuts are studied. It is shown that, for some four--fermion final states, the mass effects become sizeable to the extent that they may affect the accuracy of theoretical predictions which is required to be better than 1%.

hep-ph↗
arXiv1999

The hard bremsstrahlung correction to e^+ e^- -> 4f with finite fermion masses: results for e^+ e^- -> u d-bar mu^- nu

An improved efficient method of calculating the hard bremsstrahlung correction to e^+ e^- -> 4f for non-zero fermion masses is presented. The non-vanishing fermion masses allow us to perform the phase space integrations to the very collinear limit. We therefore can calculate cross sections independent of angular cuts. Such calculations are important for background studies. Results are presented for the total and some differential cross sections for e^+ e^- -> u d-bar mu^- nu and the corresponding hard bremsstrahlung process. The latter is of particular interest for a detailed investigation of the effects of final state radiation. In principle, the process e^+ e^- -> u d-bar mu^- nu gamma is also interesting since it helps to set bounds on possible anomalous triple and quartic gauge boson couplings involving photons. The size of mass effects is illustrated by comparing the final states u d-bar mu^- nu (gamma), c s-bar mu^- nu (gamma) and u d-bar tau^- nu(gamma).

hep-ph↗
arXiv1998

On the energy dependence of hadronic $B_c$ production

An estimate is presented of the production cross section of $B_c$ mesons between threshold and LHC energies using lowest-order perturbation theory and non-relativistic bound state approximation. It is shown that the ratio of the production cross sections for $B_c$ mesons and for $b$ quarks varies strongly with energy.

hep-ph↗
arXiv1994

Search for New Physics in e-e- Scattering

Considering the physics potential of an e-e- collider in the TeV energy range, we indicate a few interesting examples for exotic processes and discuss the standard model backgrounds. Focussing on pair production of weak gauge bosons, we report some illustrative predictions.

hep-ph↗
arXiv1994

On the Significance of the Electroweak Precision Data

We elaborate on a recently suggested effective Lagrangian for charged-current and neutral-current electroweak interactions which in comparison with the standard electroweak theory contains three free parameters $Δx, Δy$, $\varepsilon$ which quantify different sources for violations of $SU(2)$ symmetry. Within the standard $SU(2)_I \times U(1)_Y$ electroweak theory, we present both exact and very much refined approximate analytical one-loop expressions for these parameters in terms of the canonical input, $G_μ, \MZ$, $\alpz$, the top-quark mass, $\Mt$, and the Higgs-boson mass, $\MH$. We reemphase the importance of discriminating between the {\it empirically well-known purely fermionic} (vacuum polarization) contributions to $Δx, Δy$, $\varepsilon$ and the {\it empirically unknown bosonic} ones with respect to present and future electroweak precision tests. The parameters $Δx$ and $\varepsilon$ are hardly affected by standard bosonic corrections, while the full one-loop results for $Δy$ differ appreciably from the ones obtained by taking into account fermion loops only. A detailed comparison with the experimental data on $\MWpm/\MZ$, $\bar\sw^2$, $Γ_l$ shows that these data start to become accurate enough to be sensitive to standard (bosonic) contributions to $Δy$ beyond fermion loops.

hep-ph↗
arXiv1993

On the Interpretation of the Electroweak Precision Data

The recent precision electroweak data on $Γ^l, \bar s^2_W$ and $M_W/M_Z$ are compared with the tree-level and the dominant-fermion-loop as well as the full one-loop standard-model predictions. While the tree-level predictions are ruled out, the dominant-fermion-loop predictions, defined by using $α(M^2_Z)\cong 1/128.9$ in the tree-level formulae, as well as the full one-loop predictions are consistent with the experimental data. Deviations from the dominant-fermion-loop predictions are quantified in terms of an effective Lagrangian containing three additional parameters which have a simple meaning in terms of $SU(2)$ symmetry violation. The effective Lagrangian yields the standard one-loop predictions for specific values of these parameters, which are determined by $m_t$ and $m_H$.

hep-ph↗