arXiv subjects

Yu. L. Dokshitzer

Publications and source records attributed to Yu. L. Dokshitzer.

48 records · Page 3Linked to original sources

arXiv1996

The Landau-Pomeranchuk-Migdal effect in QED

The calculation of the radiative energy loss encountered by a fast charged particle which undergoes multiple scattering is being investigated. A detailed derivation of the Landau-Pomeranchuk-Migdal coherent effect in QED is given, focusing on the specific feature of the Coulomb interaction. As a result the radiation intensity per unit length in the coherent regime is shown to be proportional to $\sqrt ω$ for a photon energy $ω$ times a logarithmic enhancement which is determined exactly.

hep-ph↗

arXiv1996

QCD

We discuss QCD studies that will be possible at LEP2. We examine both experimental and theoretical aspects of jets, fragmentation functions, multiplicities and particle spectra.

hep-ph↗

arXiv1996

Dispersive Approach to Power-Behaved Contributions in QCD Hard Processes

We consider power-behaved contributions to hard processes in QCD arising from non-perturbative effects at low scales which can be described by introducing the notion of an infrared-finite effective coupling. Our method is based on a dispersive treatment which embodies running coupling effects in all orders. The resulting power behaviour is consistent with expectations based on the operator product expansion, but our approach is more widely applicable. The dispersively-generated power contributions to different observables are given by (log-)moment integrals of a universal low-scale effective coupling, with process-dependent powers and coefficients. We analyse a wide variety of quark-dominated processes and observables, and show how the power contributions are specified in lowest order by the behaviour of one-loop Feynman diagrams containing a gluon of small virtual mass. We discuss both collinear safe observables (such as the e+e- total cross section and τhadronic width, DIS sum rules, e+e- event shape variables and the Drell-Yan K-factor) and collinear divergent quantities (such as DIS structure functions, e+e- fragmentation functions and the Drell-Yan cross section).

hep-ph↗

arXiv1995

Are IR Renormalons a Good Probe for the Strong Interaction Domain?

We study the origin of non-analyticity in α_s of a short-distance QCD observable to demonstrate that the infrared renormalons, the same-sign factorial growth of the perturbative expansion, is a universal phenomenon that originates entirely from the small coupling domain. In particular, both the position and the nature of the singularity of the Borel transform of the perturbative series prove to be independent of whether the running coupling α(k^2) becomes singular at some finite scale ("Landau pole"), or stays finite down to k^2=0. We argue that getting hold of the infrared renormalons per se can help next to nothing in quantifying non-perturbative effects.

hep-ph↗

arXiv1995

Specific Features of Heavy Quark Production. LPHD approach to heavy particle spectra

Perturbative QCD formula for inclusive energy spectra of heavy quarks from heavy quark initiated jets which takes into account collinear and/or soft logarithms in all orders, the exact first order result and two-loop effects is applied to distributions of heavy flavoured hadrons in the framework of the LPHD concept. Fits to experimentally measured charm and bottom mean energy losses result in $α_{\MSbar}(M_Z)=0.125\pm 0.003\pm 0.004$ and $(2\GeV)^{-1}\int_0^{2\GeV} dk α_s^{eff}(k)= 0.18\pm 0.01\pm 0.02$ with $α_s^{eff}$ an infrared finite effective QCD coupling.

hep-ph↗

arXiv1995

Calculation of Power Corrections to Hadronic Event Shapes

We compute power corrections to hadronic event shapes in $e^+e^-$ annihilation, assuming an infrared regular behaviour of the effective coupling $α_s$. With the integral of $α_s$ over the infrared region as the only non-perturbative parameter, also measured in heavy quark physics, we can account for the empirical features of $1/Q$ corrections to the mean values of various event shapes.

hep-ph↗

arXiv1994

Induced Gluon Radiation in a QCD Medium

Soft gluon radiation induced by multiple scattering of a fast quark or gluon propagating through QCD matter is discussed. After revisiting the Landau-Pomeranchuk-Migdal effect in QED we show that large formation times of bremsstrahlung quanta determine the QCD radiation intensity (in analogy to QED) and derive the gluon energy spectrum. Coherent suppression takes place as compared to the Bethe-Heitler situation of independent emissions. As a result the energy loss of fast partons in a QCD medium depends on the incident energy $E$ similarly to QED, $-dE/dz \propto \sqrt{E}$.

hep-ph↗

arXiv1994

Gluon Radiation and Energy Losses in Top Quark Production

The emission of energetic gluons in $\tt$ production in $\ee$ annihilation can have important experimental consequences, in particular on top quark mass measurements. We present compact, analytical expressions for the gluon energy distribution and its average value at first order in QCD perturbation theory. Our results are valid for arbitrary masses, collision energies and production currents. We pay particular attention to top quark production near threshold, and show that in certain cases the soft gluon approximation is insufficient to describe the radiation spectrum.

hep-ph↗

arXiv1993

Gluon Radiation and Top Width Effects

The large width of the top quark influences the way gluons are radiated in top events, giving rise to interesting interference effects in top production and decay. We discuss top width effects in soft guon radiation in $\ee \to \tt$ at high energies and near $\tt$ threshold.

hep-ph↗

arXiv1993

Soft Photons in $W^+W^-$ Production at LEP200

The pattern of soft photon radiation in $\ee\to\ww$ has a rich structure, with contributions from photon emission off the initial state and off the final state particles both before and after decay. In particular, the interference between the contributions involving the decaying $W$'s depends on the decay width. We review the theoretical result for the radiation pattern, and present predictions for LEP200, {\it i.e.} in $\ee$ annihilation just above $\ww$ threshold.

hep-ph↗

arXiv1993

Properties of Soft Radiation Near $\tt$ and $W^+W^-$ Threshold

We discuss the characteristic interference features of soft radiation in the threshold production of heavy unstable particles: soft gluon radiation in $\ee \to \tt$ and soft photon radiation in $\ee \to \ww$. We show that the heavy particle decay width controls the interference between the emission off the final state particles. As a result, the radiation pattern may provide a way of measuring the decay width of the heavy particles.

hep-ph↗

arXiv1992

Top Width Effects in Soft Gluon Radiation

Soft gluons radiated in top quark production and decay can interfere in a way that is sensitive to the top width. We show how the width affects the gluon distribution in $e^+e^- \rightarrow t {\bar t}$ and discuss prospects for measuring $Γ$ from gluons radiated near $\tt$ threshold.

hep-ph↗