Erwin Mirkes

Dijet production at HERA in next-to-leading order

Abstract 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 → 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.

QCD corrections to toponium production at hadron colliders.

Toponium production at future hadron colliders is investigated. Perturbative QCD corrections to the production cross section for gluon fusion are calculated as well as the contributions from gluon-quark and quark-antiquark collisions to the total cross section. The dependence on the renormalization and factorization scales and on the choice of the parton distribution functions is explored. QCD corrections to the branching ratio of ηt into γγ are included and the two-loop QCD potential is used to predict the wave function at the origin. The branching ratio of ηt into γZ, ZZ, HZ and W W is compared with the γγ channel.

Spin effects and factorization in the Drell-Yan process

We discuss the idea that the nontrivial vacuum structure in QCD may induce transverse momentum and spin correlations of the initial state partons in Drell-Yan type reactions, i.e. in hadron-hadron collisions with production of a vector bosonV=γ*,Z,W±. Transverse momentum correlations are found to have practically no effect on observable quantities, but spin correlations have drastic consequences for the polarization density matrices of theV-bosons. We therefore propose measurements of theV polarization as a good test for the basic factorization hypothesis which, so far, has been assumed to be valid in numerous applications of the naive and QCD-improved parton model. We compare our ansatz for a spin correlation violating factorization with data from the NA 10 collaboration onγ* production inπ−N scattering. We find that the data give an indication of spin correlations of the partons in the initial state to be present.

CP violation in semileptonic τ decays with unpolarized beams

Abstract CP violating signals in semileptonic τ decays are studied. These can be observed in decays of unpolarized single τs 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.

Angular distributions in semileptonic τ decays

Abstract A complete description of angular distributions in terms of four structure functions is given for the three pion system in a spin one state resulting from the decay of polarized τs. Of particular importance is the case where the τs are produced in e + e − annihilation and the τ rest frame cannot be reconstructed. It will be demonstrated that the structure functions can be measured even in this case, even with unpolarized τs. The importance of the angle ψ, which denotes the angle between the direction of the laboratory and the τ as seen from the three pion rest frame is emphasized. Predictions for the structure functions based on a specific model for the hadronic current will be presented.

Tau decays into three pseudoscalar mesons

In this paper we compute the branching ratios of the tau decays into three mesons. The hadronic matrix elements are obtained by first using the structure of the chiral currents and that of the Wess-Zumino anomaly and finally implementing all possible low-lying resonances in the different channels.

Measuring the Wess-Zumino anomaly in [tau] decays

We propose to measure the Wess-Zumino anomaly contribution by considering angular distributions in the decays [tau][r arrow][nu][sub [tau]][eta][pi][sup [minus]][pi][sup 0], [tau][r arrow][nu][sub [tau]][ital K][sup [minus]][pi][sup [minus]][ital K+], and [tau][r arrow][nu][sub [tau]][ital K][sup [minus]][pi][sup [minus]][pi][sup +]. Radial excitations of the [ital K][sup *], which cannot be seen in [ital e][sup +]+[ital e][sup [minus]], should be observed in the [ital K][sup [minus]][pi][sup +][pi][sup [minus]] decay channel.

Heavy quark production at a photon linear collider

Heavy quark production at future Compton colliders is investigated. The impact of polarization has been studied. Perturbative QCD corrections to the effective cross section are calculated and found to be at the level of 40% for ae+e− collider of 500 GeV and a top quark mass of 150 GeV. The ηt resonance structure is incorporated.

Forward Jet Production at DESY HERA in the Low {ital x} Regime in Next-to-Leading Order

The production of forward jets of transverse momentum p{sub T}(j){approx}Q and large momentum fraction x{sub jet}{gt}x probes the onset of Balitsky-Fadin-Kuraev-Lipatov (BFKL) dynamics at DESY HERA. A full O({alpha}{sup 2}{sub s}) 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. {copyright} {ital 1997} {ital The American Physical Society}

The Scalar contribution to tau --> k pi tau-neutrino

We consider the scalar form factor in