arXiv subjects
Publications and source records attributed to Jiri Chyla.
Interactions of virtual photons are analyzed in terms of their parton distribution functions. It is shown that the concept of parton distribution functions is phenomenologically very useful even for highly virtual photonds involved in hard collisions. The role of the longitudinal photons for proper interpretation of the data on jet cross--sections in the region of moderate photon virtualities accessible at HERA is explored.
Interactions of virtual photons are analyzed in terms of photon structure. It is argued that the concept of parton distribution functions is phenomenologically very useful even for highly virtual photons involved in hard collisions. The role of longitudinal photons for proper interpretation of jet cross--sections in the region of moderate virtualities accessible at HERA is investigated.
Factorization scheme analysis of $F_2^γ(x,Q^2)$ in the next-to-leading order QCD is revisited. It is emphasized that the presence of the inhomogeneous term in the evolution equations for quark distribution functions of the photon implies subtle but important difference in the way factorization mechanism works in photon-hadron and photon-photon collisions as compared to the hadronic ones. It is argued that none of the existing NLO analyses of $F_2^γ(x,Q^2)$ takes this difference properly into account. The source of the ensuing incompleteness is traced back to the misinterpretation of the behaviour of $q^γ(x,M)$ as a function of $α_s(M)$. Parton model interpretation of the so called ``constant terms'' in the LO photonic coefficient function $C_γ^{(0)}(x)$ is given and smooth transition between the properties of virtual and real photon analyzed. Finally phenomenological consequences of this analysis are discussed.
For theoretically consistent determination of $α_s$ from jet rates in deep inelastic scattering the dependence on $α_s$ of parton distribution functions is in principle as important as that of hard scattering cross-sections. For the kinematical region accessible at HERA we investigate in detail numerical importance of these two sources of the $α_s$ dependence of jet rates.
For theoretically consistent determination of $α_s$ from jet rates in deep inelastic scattering the dependence on $α_s$ of parton distribution functions is in principle as important as that of hard scattering cross--sections. For the kinematical region accessible at HERA we investigate in detail numerical importance of these two sources of the $α_s$ dependence of jet rates.
The idea of ``dynamically'' generated parton distribution functions, based on regular initial conditions at low momentum scale, is reanalyzed with particular emphasize paid to its compatibility with the factorization mechanism. Basic consequences of this approach are discussed and compared to those of the conventional approach, employing singular initial distribution functions.
The question of the uniqueness of the Brodsky--Lepage--Mackenzie procedure for fixing the renormalization scale in perturbative QCD is discussed. It is shown that the resulting finite order approximants are as ambiguous as the original truncated perturbative expansions. This inherent ambiguity of the BLM procedure undermines the recent attempts to define ``genuine'' higher order perturbative corrections.
We discuss uncertainties of QCD predictions for the hadronic width of the $Z^0$ boson. Emphasis is put on quantitative estimates, taking into account the current precision of experimental data.
The accuracy of the conventional treatment of quark mass thresholds in the QCD running coupling constant $α_s$, based on the step approximation to the $β$--function, is investigated. The errors of extrapolating $\ase(μ)$ from low energies to $μ=M_Z$, implied by this approximation, are shown to be of the same magnitude as the typical next--to--next--to--leading order contributions to \as and tend to increase the resulting \as. The importance of the proper choice of matching points is emphasized.