arXiv subjects

Erwin Mirkes

Publications and source records attributed to Erwin Mirkes.

16 recordsLinked to original sources

arXiv1997

Effects of Jet Azimuthal Angular Distributions on Dijet Production Cross Sections in DIS

A Monte Carlo study of the azimuthal angular distribution around the virtual boson-proton beam axis for dijet events in DIS at HERA is presented. In the presence of typical acceptance cuts on the jets in the laboratory frame, the azimuthal distribution is dominated by kinematic effects rather than the typical $\cosϕ$ and $\cos 2ϕ$ dependence predicted by the QCD matrix elements. This implies that the $ϕ$ dependent part of the QCD matrix elements contributes even to the dijet production cross section. Neglecting this $ϕ$ dependence leads to an error of about 5-8\% in the production cross section for typical acceptance cuts in the laboratory frame. We also present first NLO results on the $ϕ$-decorrelation of the jets through NLO effects.

hep-ph↗

arXiv1997

Jet Production in DIS at NLO

Dijet production in DIS is an important laboratory for testing our understanding of perturbative QCD. Flexible NLO Monte Carlo programs allow to investigate general jet definition schemes. For forward jet production at $p_{Tj} \approx Q$ and $x_{jet} >> x$ the NLO predictions fall well below HERA data, thus providing evidence for BFKL dynamics.

hep-ph↗

arXiv1997

Isospin Violation in tau -> 3 pi nu_tau

Isospin violating signals in the tau -> 3 pi nu_tau decay mode are discussed. For the tau -> pi^- pi^- pi^+ nu_tau decay mode, isospin violation arises from the vector current contribution in the tau -> omega pi nu_tau decay with the subsequent isospin violating omega decay into pi^+ pi^-. We demonstrate that such effects may be observed in presently available data through the measurement of the interference effects of these vector current contributions with the dominating axial vector current, i.e. through a measurement of the structure functions W_F,W_G,W_H and W_I. In the case of the tau -> pi^0 pi^0 pi^- nu_tau decay mode, a vector current contribution is generated by eta pi mixing in the decay chain tau -> eta rho nu_tau -> pi^0 pi^0 pi^- nu_tau. We find that this effect is rather small, the magnitude of the associated interference terms being too low for present statistics.

hep-ph↗

arXiv1996

Theoretical Aspects of $τ\to K h (h) ν_τ$ Decays and Experimental Comparisons

Predictions for decay rates and distributions for $τ$ decays into final states with kaons are discussed and compared with recent measurements. Special emphasis is put on new constraints for the vector current contribution in the $KKπ$ decay modes. For the $Kππ$ modes, disagreements with the experimental results can be traced back to the $K_1$ widths.

hep-ph↗

arXiv1996

Structure Functions in Semihadronic Tau Decays

We review a variety of topics related to hadronic structure functions in exclusive semihadronic tau decays. We introduce the concept of structure functions and summarize the most important concepts. We then calculate the decay $τ\to 3 πν_τ$ for very small hadronic invariant mass to one loop in Chiral Perturbation Theory. New interesting features emerge with respect to the known results at tree level, in particular for the structure functions $w_D$ and $w_E$. We discuss the prospects for experimental verification of our predictions. Finally, we discuss various issues at higher $Q^2$, related to hadronic resonance physics. Here we consider $2π$, $πK$, $3 π$, $K πK$ and $πK π$ hadronic final states.

hep-ph↗

arXiv1996

Jet Production in Deep Inelastic Scattering at Next-to-Leading Order

NLO corrections to jet cross sections in DIS at HERA are studied, with particular emphasis on the two jet final state. High jet transverse momenta are a good criterion for the applicability of fixed order perturbation theory. A ``natural'' scale choice is the average $k_T^B$ of the jets in the Breit frame, which suggest analyzing the data in different $ $ intervalls.

hep-ph↗

arXiv1996

Fixed-Order QCD Backgrounds to BFKL Dynamics in Forward Jet Production

hep-ph↗

arXiv1996

Forward Jet Production at HERA in the Low $x$ Regime in Next-to-Leading Order

The production of forward jets of transverse momentum $p_T(j)\approx Q$ and large momentum fraction $x_{jet}\gg x$ probes the onset of BFKL dynamics at HERA. A full ${\cal O}(α_s^2)$ calculation of the inclusive forward jet cross section is presented and compared to the expected BFKL cross section. The kinematical region populated by these events and the scale dependence of the fixed order perturbative QCD cross sections are discussed.

hep-ph↗

arXiv1996

NLO Corrections to Jet Cross Sections in DIS

Next-to-leading order corrections to jet cross sections in deep inelastic scattering at HERA are studied. The predicted jet rates allow for a precise determination of $α_s(μ_R)$ at HERA over a wide range of $μ_R$. We argue, that the ``natural'' renormalization and factorization scale is set by the average $k_T^B$ of the jets in the Breit frame and suggest to divide the data in corresponding $ $ intervals. Some implications for the determination of the gluon density and the associated forward jet production in the low $x$ regime at HERA are briefly discussed.

hep-ph↗

arXiv1996

Dijet Production at HERA in Next-to-Leading Order

Two-jet cross sections in deep inelastic scattering at HERA are calculated in next-to-leading order. The QCD corrections are implemented in a new $ep\rightarrow n$ jets event generator, MEPJET, which allows to analyze arbitrary jet definition schemes and general cuts in terms of parton 4-momenta. First results are presented for the JADE, the cone and the $k_T$ schemes. For the $W$-scheme, disagreement with previous results and large radiative corrections and recombination scheme dependencies are traced to a common origin.

hep-ph↗

arXiv1996

QCD Corrections to Jet Cross Sections in DIS

hep-ph↗

arXiv1996

Jet Production in Deep Inelastic Scattering at HERA

Two-jet cross sections in deep inelastic scattering at HERA are calculated in next-to-leading order. The importance of higher order corrections and recombination scheme dependencies is studied for various jetalgorithms. Some implications for the determination of $α_s(μ_R^2)$, the determination of the gluon density and the associated forward jet production in the low $x$ regime at HERA are briefly discussed.

hep-ph↗

arXiv1996

The Scalar Contribution to $τ\to K πν_τ$

We consider the scalar form factor in $τ\to Kπν_τ$ decays. It receives contributions both from the scalar resonance $K_0^*(1430)$ and from the scalar projection of off-shell vector resonances. We construct a model for the hadronic current which includes the vector resonances $K^*(892)$ and $K^*(1410)$ and the scalar resonance $K_0^*(1430)$. The parameters of the model are fixed by matching to the $O(p^4)$ predictions of chiral perturbation theory. Suitable angular correlations of the $Kπ$ system allow for a model independent separation of the vector and scalar form factor. Numerical results for the relevant structure functions are presented.

hep-ph↗

arXiv1995

Decay Rates, Structure Functions and New Physics Effects in Hadronic Tau Decays

Hadronic decays rates of the $τ$ lepton into multi meson final states are presented. The structure of the hadronic matrix elements for various decay modes is discussed. The formalism of structure functions allows for a detailed test of these matrix elements. Various correlations are discussed which are sensitive to possible CP violation and new physics effects in the decay modes.

hep-ph↗

arXiv1995

Tau Decays into Kaons

Predictions for semi-leptonic decay rates of the tau lepton into two and three meson final states with one or two kaons are derived, including a discussion of K_S pi- K_S, K_L pi- K_L and K_S pi- K_L. The hadronic matrix elements are expressed in terms of form factors, which can be predicted by chiral Lagrangians supplemented by informations about all possible low-lying resonances in the different channels. Isospin symmetry relations among the different final states are carefully taken into account. The calculated branching ratios are compared with measured decay rates where data are available.

hep-ph↗

arXiv1993

Pseudoscalar Mass Effects in Decays of Taus with Three Pseudoscalar Mesons

We study the effects of non-vanishing pseudoscalar masses in $τ$ decays into three mesons. The hadronic matrix elements are obtained by using the generalized structure of the chiral currents with nonvanishing pseudoscalar masses and implementing the low-lying resonances in the different channels. We demonstrate that suitable angular distributions are sensitive to the mass effects in the chiral Langrangian. Numerical results for the rele\-% vant structure functions are given for the decay modes $τ\rightarrow νπ^-π^-π^+$, $νK^-π^-π^+$ and $νK^-π^-K^+$.

hep-ph↗