Studying top quark pair production at a linear collider with a program 'eett6f'

Some features of a program 'eett6f' for top quark pair production and decay into six fermions at linear colliders are discussed. Lowest order standard model predictions for cross sections of some six fermion channels and for the top quark decay width are confronted with the predictions obtained within a model with an anomalous Wtb coupling. The question of wether non doubly resonant background can easily be reduced by imposing kinematical cuts is addressed.Comment: 10 pages, 8 figures, presented at the Cracow Epiphany Conference on Heavy Flavors,Cracow, Poland, January 3--6, 200

Secondary lepton distributions as a probe of the top--higgs coupling at the LHC

The differential distributions in rapidity and angles of the secondary lepton in the associated production of the top quark pair and higgs boson in proton-proton collisions at the LHC are quite sensitive to the top-higgs coupling. However, the effects of anomalous couplings of the most general t anti-t h interaction with operators of dimension-six that are clearly visible in the signal of the associated production of the top quark pair and higgs boson are to large extent obscured by the background sub-processes with the same final state. This means that analyses of such effects, in addition to higher order corrections that are usually calculated for the on-shell top quarks and higgs boson, should include their decays and possibly complete off resonance background contributions to the corresponding exclusive reactions.Comment: 12 pages, 6 figures, version accepted for publication in JHE

Photon radiation in e+e−→e^+e^-\to hadrons at low energies with CARLOMAT 3.1

We present a sample of results for the cross sections of several processes of low energetic $e^+e^-$ annihilation into final states containing pions accompanied by one or two photons, or a light lepton pair. The results, which have been obtained with a new version of a multipurpose Monte Carlo program CARLOMAT, labelled 3.1, demonstrate new capabilities of the program which, among others, include a possibility of taking into account either the initial or final state radiation separately, or both at a time, and a possibility of inclusion of the electromagnetic charged pion form factor for processes with charged pion pairs. We also discuss some problems related to the $U(1)$ electromagnetic gauge invariance.Comment: 17 pages, 17 figures, matches version published in Eur. Phys. J.

Probing the top-Higgs coupling through the secondary lepton distributions in the associated production of the top-quark pair and Higgs boson at the LHC

We complement the analysis of the anomalous top-Higgs coupling effects on the secondary lepton distributions in the associated production of the top-quark pair and Higgs boson in proton-proton collisions at the LHC of the former work by one of the present authors by taking into account the quark-antiquark production mechanism. We also present simple arguments which explain why the effects of the scalar and pseudoscalar anomalous couplings on the unpolarized cross section of the process are completely insensitive to the sign of either of them.Comment: 12 pages, 11 figures, referee's suggestions taken into accoun

Off mass shell effects in associated production of the top quark pair and Higgs boson at a linear collider

We discuss effects related to the fact that the final state particles of a reaction e+ e- -> t \bar{t} H are actually produced and they decay off mass shell. For the intermediate mass Higgs boson, which decays preferably into a b\bar{b}-quark pair, the reaction will be observed through reactions with 8 fermions in the final state. Such reactions, already in the lowest order of the standard model, receive contributions typically from a few dozen thousands of the Feynman diagrams, the vast majority of which constitute background to the signal of associated production of the top quark pair and Higgs boson. In order to illustrate pure off mass shell effects we neglect the background contributions and compare the `signal' cross section with the cross section in the narrow width approximation for e+ e- -> b u \bar{d} \bar{b} mu- \bar{nu}_mu b \bar{b}, which is one of possible detection channels of the associated production of the top quark pair and Higgs boson at a linear collider.Comment: 11 pages, 4 figures, version published in Acta Physica Polonica