arXiv subjects
Publications and source records attributed to J. Ohnemus.
We investigate soft gluon radiation in hadronic $t\bar t$ production. By taking the top quark decay properly into account, we are able to study the interplay of radiation both before and after the decay of the top quarks. The production--decay and decay--decay radiative interferences depend sensitively on the relative size of the gluon energy and the decay width. Radiation patterns for various production mechanisms are compared.
Single-lepton plus jets signals from $t\bar t$ production at hadron colliders generally give more spherically symmetrical events than the principal backgrounds from $W$ production. We show that sphericity and aplanarity criteria, applied to lepton plus neutrino plus four jet final states at the Fermilab Tevatron $p\bar p$ collider, help to discriminate; they can be used either to validate an eventual top signal or simply to reduce background. An alternative circularity criterion in the transverse plane is less successful.
The process $p \pbar \rightarrow W^{\pm}γ+ X \rightarrow \ell^\pm νγ+ X$ is calculated to ${\cal O}(α_s)$ for general $CP$ conserving $WWγ$ couplings. At the Tevatron center of mass energy, the QCD corrections to $Wγ$ production are modest, and the Born and inclusive ${\cal O}(α_s)$ cross sections have similar sensitivities to the effects of anomalous couplings. At supercollider energies, the inclusive QCD corrections are large at high photon transverse momenta, reducing the sensitivity to non-standard $WWγ$ couplings by up to a factor~2. The size of the QCD corrections can be reduced significantly, and a large fraction of the sensitivity lost can be regained, if a jet veto is imposed.
The ratios ${\cal R}_{γ,\ell}=B(Z\to\ell^+\ell^-)\cdotσ(Zγ) /\allowbreak B(W\to\ellν)\cdotσ(W^\pmγ)$, ${\cal R}_{γ, ν}= B(Z\to\barνν)\cdotσ(Zγ)/\allowbreak B(W\to\ellν)\cdotσ(W^ \pmγ)$, ${\cal R}_{Wγ}=σ(W^\pmγ)/\allowbreakσ(W^\pm)$, and ${\cal R}_{Zγ}=σ(Zγ)/\allowbreakσ(Z)$ are studied as tools to probe the electroweak boson self-interactions. As a function of the minimum photon transverse momentum, ${\cal R}_{γ,\ell}$ and ${\cal R}_{ γ,ν}$ are found to directly reflect the radiation zero present in $W^ \pmγ$ production in the Standard Model. All four ratios are sensitive to anomalous $WWγ$ and/or $ZZγ/Zγγ$ couplings. The sensitivity of the cross section ratios to the cuts imposed on the final state particles, as well as the systematic uncertainties resulting from different parametrizations of parton distribution functions, the choice of the factorization scale $Q^2$, and from higher order QCD corrections are explored. Taking into account these uncertainties, sensitivity limits for anomalous three gauge boson couplings, based on a measurement of the cross section ratios with an integrated luminosity of 25~pb$^{-1}$ at the Tevatron, are estimated.