A. Brandenburg

Top quark pair production and decay at hadron colliders

In ongoing and upcoming hadron collider experiments, top quark physics will play an important role in testing the Standard Model and its possible extensions. In this work we present analytic results for the differential cross sections of top quark pair productio n in hadronic collisions at next-to-leading order in the QCD coupling, keeping the full dependence on the spins of the top quarks. These results are combined with the corresponding next-to-leading order results for the decay of polarized top quarks into dilepton, lepton plus jets, and all jets final states. As an ap plication we predict double differential angular distributions which are due to the QCD-induced top quark spin correlations in the intermediate state. In addition to the analytic results, we give numerical results in terms of fit functions that can easily be used in an experimental analysis.

Next-to-Leading Order QCD Corrections to Three-Jet Cross Sections with Massive Quarks ∗

We calculate the cross section for e{sup +}e{sup {minus}} annihilation into three jets for massive quarks at next-to-leading order in perturbative QCD, both on and off the Z resonance. Our computation allows the implementation of any jet clustering algorithm. We give results for the three-jet cross section involving b quarks for the JADE and Durham algorithms at c.m.energies {radical}(s)=m{sub Z} . We also discuss a three-jet observable that is sensitive to the mass of the b quark. {copyright} {ital 1997} {ital The American Physical Society}

Next-to-leading order QCD corrections and massive quarks in e+e− → 3 jets☆

Abstract We present in detail a calculation of the next-to-leading order QCD corrections to the process e + e − → 3 jets with massive quarks. To isolate the soft and collinear divergencies of the four-parton matrix elements, we modify the phase space slicing method to account for masses. Our computation allows for the prediction of oriented three-jet events involving heavy quarks, both on and off the Z resonance, and of any event shape variable which is dominated by three-jet configurations. We show next-to-leading order results for the three-jet fraction, the differential two-jet rate, and for the thrust distribution at various c.m. energies.

Next-to-leading order QCD corrections to top quark spin correlations at hadron colliders: the reactions and

Abstract Future hadron collider experiments are expected to record large to huge samples of t t events. The analysis of these data with respect to t t spin-spin correlations requires precise predictions of the production of these quark pairs in a general spin configuration. Therefore we have computed, at next-to-leading order (NLO) in the QCD coupling, the spin density matrices describing t t production by quark antiquark annihilation, which is the dominant production process at the Tevatron. Moreover we have computed the strength of the t t spin correlation at NLO, using various spin quantization axes.

Measurement of the running b-quark mass using e+e events

Abstract We have studied the determination of the running b-quark mass, mb(MZ), using Z0 decays into 3 or more hadronic jets. We calculated the ratio of ≥3-jet fractions in e+e − →b b versus e+e − →q l q l (ql = u or d or s) events at next-to-leading order in perturbative QCD using six different infra-red- and collinear-safe jet-finding algorithms. We compared with corresponding measurements from the SLD Collaboration and found a significant algorithm-dependence of the fitted mb(MZ) value. Our best estimate, taking correlations into account, is mb(MZ) = 2.56±0.27 (stat.) +0.28−0.38 (syst.) +0.49−1.48 (theor.) GeV/c2.

QCD corrections to decay distributions of neutral Higgs bosons with (in)definite CP parity

We compute the order

CP violation beyond the standard model and tau pair production in e+ e- collisions

{\ensuremath{\alpha}}_{s}

Instantons in lepton pair production

QCD corrections to the density matrix for the decay of a neutral Higgs boson

Next-to-leading order QCD corrections to top quark spin correlations at hadron colliders: the reactions

\ensuremath{\varphi}

g g \to t {\bar t} (g)

with (in)definite