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E. Mirkes

Publications and source records attributed to E. Mirkes.

At least 19 recordsLinked to original sources
arXiv1998

Asymmetry distributions and mass effects in dijet events at a polarized HERA

The asymmetry distributions for several kinematic variables are considered for finding a systematic way to maximize the signal for the extraction of the polarized gluon density. The relevance of mass effects for the corresponding dijet cross section is discussed and the different approximations for including mass effects are compared. We also compare via the programs Pepsi and Mepjet two different Monte Carlo (MC) approaches for simulating the expected signal in the dijet asymmetry at a polarized HERA.

hep-ph↗
arXiv1997

Theoretical Aspects of $τ\to Kππν_τ$ Decays

Predictions based on the chirally normalized vector meson dominance model for decay rates and distributions of $τ$ decays into $Kππν_τ$ final states are discussed. Disagreements with experimental results can be traced back to the $K_1$ widths.

hep-ph↗
arXiv1997

QCD Corrections to Jet Production in Polarized $ep$ Scattering

Next-to-leading order QCD predictions for 1-jet and 2-jet cross sections in polarized deep inelastic scattering at HERA energies are presented. Whereas the QCD corrections to the total polarized cross section are very large, only moderate corrections are found for the dijet cross sections.

hep-ph↗
arXiv1997

CP Violation from Charged Higgs Exchange in Hadronic Tau Decays with Unpolarized Beams

CP violating signals in semileptonic $τ$ decays induced by an exotic scalar exchange are studied in a completely model-independent way. These can be observed in decays of unpolarized single $τ$'s even if their rest frame cannot be reconstructed. No beam polarization is required. The importance of the two-meson channel, in particular the $Kπ$ final state is emphasized.

hep-ph↗
arXiv1997

Theory of Jets in Deep Inelastic Scattering

The large center of mass energy and increasing statistical precision for a wide range of hadronic final state observables at the HERA lepton-proton collider has provided a detailed testing ground for QCD dynamics. Fully flexible next-to-leading order calculations are mandatory on the theoretical side for such tests and will be discussed in detail. Next-to-leading order QCD predictions for one- and two-jet cross sections in deep inelastic scattering with complete neutral current ($γ^\ast$ and/or $Z$) and charged current ($W^\pm$) exchange together with leading order results for three- and four-jet final states are presented. The theoretical framework, based on the phase space slicing method and the use of universal crossing functions, is described in detail. All analytical formulae necessary for the next-to-leading order calculations are provided. The numerical results are based on the fully differential $ep \to n$ jets event generator \docuname which allows to analyze any infrared and collinear safe observable and general cuts in terms of parton 4-momenta. The importance of higher order corrections is studied for various jet algorithms. Implications and comparisons with (ongoing) experimental analyses for jet cross sections at high $Q^2$, the determination of $α_s(μ_R)$, the gluon density, power corrections in event shapes and the associated forward jet production in the low $x$ regime at HERA are discussed. A study of jet cross sections in polarized electron and polarized proton collisions shows that dijet events provide a good measurement of the polarized gluon distribution $Δg(x_g)$, in a region, where $x_g Δg(x_g)$ is expected to show a maximum.

hep-ph↗
arXiv1996

Prospects for Measuring Delta G from Jets at HERA with Polarized Protons and Electrons

The measurement of the polarized gluon distribution function Delta G(x) from photon-gluon fusion processes in electron-proton deep inelastic scattering producing two jets has been investigated. The study is based on the MEPJET and PEPSI simulation programs. The size of the expected spin asymmetry and corresponding statistical uncertainties for a possible measurement with polarized beams of electrons and protons at HERA have been estimated. The results show that the asymmetry can reach a few percent, and is not washed out by hadronization and higher order processes.

hep-ph↗
arXiv1996

CP Violation in Semileptonic $τ$ Decays with Unpolarized Beams

CP violating signals in semileptonic $τ$ decays are studied. These can be observed in decays of unpolarized single $τ$'s even if their rest frame cannot be reconstructed. No beam polarization is required. The importance of the two meson channel, in particular the $Kπ$ final state is emphasized.

hep-ph↗
arXiv1996

Prospects for Measuring $Δg$ from Jets at HERA with Polarized Protons

The measurement of the polarized gluon distribution function $Δg(x)$ from photon gluon fusion processes in electron proton deep inelastic scattering producing two jets has been investigated. The study is based on the MEPJET simulation program. The size of the expected spin asymmetry and corresponding statistical uncertainties for a possible measurement with polarized beams of electrons and protons at HERA have been estimated. The results show that the asymmetry can reach a few percents.

hep-ph↗
arXiv1995

Exclusive Semileptonic Tau Decays

We review current issues in exclusive semileptonic tau decays. We present the formalism of structure functions, and then discuss predictions for final states with kaons, for decays into four pions and for radiative corrections to the decay into a single pion. Implications for testing the standard model at low energies are discussed.

hep-ph↗
arXiv1995

DISJET 1.2: A Monte Carlo Program for Jet Cross Section Calculations in Deep Inelastic Scattering

We present a new parton level Monte Carlo program for the calculation of jet cross sections in Deep Inelastic Scattering based on Born and next-to-leading order matrix elements. Using a class of invariant jet definition schemes, the program allows for the calculation of differential distributions of jet cross sections in the basic kinematical variables (like s, x, y, W^2, Q^2...) as well as for total jet cross sections. Various kinematical cuts can be chosen from an input file.

hep-ph↗
arXiv1995

J/Psi Decay Lepton Distribution in Hadronic Collisions

We propose the measurement of the decay angular distribution of leptons from J/Psi's produced at high transverse momentum balanced by a photon [or gluon] in hadronic collisions. The polar and azimuthal angular distribution are calculated in the color singlet model (CSM). It is shown that the general structure of the decay lepton distribution is controlled by four invariant structure functions, which are functions of the transverse momentum and the rapidity of the J/Psi. We found that two of these structure functions [the longitudinal and transverse interference structure functions] are identical in the CSM. We present analytical and numerical results in the Collins-Soper and in the Gottfried-Jackson frame.

hep-ph↗
arXiv1994

Angular Distributions of Drell-Yan Lepton Pairs at the Tevatron: Order $α_s^2$ Corrections and Monte Carlo Studies

We investigate the angular distribution of the lepton pair in the process $p \bar{p} \rightarrow γ^{\ast} + X \rightarrow \ell^+\ell^- + X$, where the virtual photon is produced at high transverse momentum. The angular distribution of the leptons is very sensitive to possible nonperturbative effects, such as a nontrivial vacuum structure of QCD, and offers a good chance to test such effects. We present complete ${\cal O}(α_s^2)$ calculations of the decay lepton distributions in the lepton pair rest frame. An order ${\cal O}(α_s)$ Monte Carlo study of the lepton angular distributions, with acceptance cuts and energy resolution smearing applied to the leptons, is also presented.

hep-ph↗
arXiv1994

Semileptonic tau decays, structure functions, kinematics and polarisation

The most general angular distribution of two or three meson final states from semileptonic decays $τ\rightarrow ππν$, $Kπν$, $πππν$, $Kππν$, $Kπν$, $KKKν$, $ηππν,\,\ldots{}$ of polarized $τ$ leptons can be characterized by 16 structure functions. Predictions for hadronic matrix elements, based on CVC and chiral Lagrangians and their relations to the structure functions are discussed. Most of them can be determined in currently ongoing high statistics experiments. Emphasis of the kinematical analysis is firstly put on $τ$ decays in $e^{+}e^{-}$ experiments where the neutrino escapes detection and the $τ$ rest frame cannot be reconstructed. Subsequently it is shown, how the determination of hadron tracks in double semileptonic events allows to fully reconstruct the $τ$ kinematics. The implications for the spin analysis are indicated.

hep-ph↗
arXiv1994

Further ways to distinguish single-lepton top quark signals from background at the Tevatron

Further kinematical variables are suggested, in which to compare the putative leptonic $W$ plus 4-jet top quark signal with the QCD background. We show that the lepton rapidity asymmetry, the $p_T$-ranking of the tagged $b$-jet, the double-tag probability, the reconstructed $t+\bar t$ invariant mass, and the lepton energy in the parent top quark rest-frame, all display interesting differences between signal and background.

hep-ph↗
arXiv1994

Z Plus Four Jets Production in Hadronic Collisions

We present first results of $Z+4$ jet cross sections at the Tevatron $p\bar p$ collider with heavy quark flavor identification. The $Z + 4$ jet channel is of particular interest as a normalizer for the $W +4$ jet background to top quark signals, as a background to a possible $t\to cZ$ flavor-changing neutral-current (FCNC) decay signal, and as a background to missing-$p_T$ signals from gluino pairs. We also calculate the different heavy flavor contributions to $W+4$ jet production. The MADGRAPH program is used to generate all leading order subprocess helicity amplitudes. We present Monte Carlo studies with separation and acceptance criteria suitable for the Tevatron experimental analyses.

hep-ph↗
arXiv1994

Calculation of Z Plus Four Jet Production at the Tevatron

We present the first calculation of $Z+4$ jet production with heavy quark flavor identification at the Tevatron $p\bar p$ collider. The $Z + 4$ jet channel is especially interesting as a normalizer for the $W +4$ jet background to top quark signals, as a background to a possible $t\to cZ$ flavor-changing neutral-current (FCNC) decay signal, and as a background to missing-$p_T$ signals from gluino pairs. We also calculate the contributions to $W+4$ jet production from all the different heavy-flavor final states. The MADGRAPH program is used to generate all leading order subprocess helicity amplitudes. We present Monte Carlo results with separation and acceptance criteria suitable for the Tevatron experimental analyses. The dependence of the cross sections on experimental cuts and the theoretical ambiguities due to the scale dependence are discussed. The predicted ($W+4$ jet)/($Z+4$ jet) ratio is insensitive to most of these choices.

hep-ph↗
arXiv1994

Structure Functions and Distributions in Semileptonic Tau Decays

Semileptonic decays of polarized $τ$ leptons are investigated. The most general angular distribution of three meson final states ($τ\rightarrow ππν,\,Kπν,\, πππν,\\ \,Kππν,\, KKπν,\, KKKν,\, ηππν,\,\ldots{}$) is discussed. It is shown, that the most general distribution can be characterized by 16 structure functions, most of which can be determined in currently ongoing high statistics experiments. Emphasis is put on $τ$ decays in $e^{+}e^{-}$ experiments where the neutrino escapes detection and the $τ$ rest frame cannot be reconstructed. The structure of the hadronic matrix elements, based on CVC and chiral lagrangians, is discussed.

hep-ph↗